greenplumn bufmgr 源码
greenplumn bufmgr 代码
文件路径：/src/backend/storage/buffer/bufmgr.c
/*-------------------------------------------------------------------------
*
* bufmgr.c
* buffer manager interface routines
*
* Portions Copyright (c) 2006-2009, Greenplum inc
* Portions Copyright (c) 2012-Present VMware, Inc. or its affiliates.
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/storage/buffer/bufmgr.c
*
*-------------------------------------------------------------------------
*/
/*
* Principal entry points:
*
* ReadBuffer() -- find or create a buffer holding the requested page,
* and pin it so that no one can destroy it while this process
* is using it.
*
* ReleaseBuffer() -- unpin a buffer
*
* MarkBufferDirty() -- mark a pinned buffer's contents as "dirty".
* The disk write is delayed until buffer replacement or checkpoint.
*
* See also these files:
* freelist.c -- chooses victim for buffer replacement
* buf_table.c -- manages the buffer lookup table
*/
#include "postgres.h"
#include <sys/file.h>
#ifdef MPROTECT_BUFFERS
#include <sys/mman.h>
#endif
#include <unistd.h>
#include "access/tableam.h"
#include "access/xlog.h"
#include "catalog/catalog.h"
#include "catalog/storage.h"
#include "executor/instrument.h"
#include "lib/binaryheap.h"
#include "miscadmin.h"
#include "pg_trace.h"
#include "pgstat.h"
#include "postmaster/bgwriter.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
#include "storage/ipc.h"
#include "storage/proc.h"
#include "storage/smgr.h"
#include "storage/standby.h"
#include "utils/rel.h"
#include "utils/resowner_private.h"
#include "utils/faultinjector.h"
#include "pgstat.h"
#include "access/heapam.h"
#include "access/aosegfiles.h"
#include "access/aocssegfiles.h"
#include "cdb/cdbappendonlyam.h"
#include "utils/timestamp.h"
/* Note: these two macros only work on shared buffers, not local ones! */
#define BufHdrGetBlock(bufHdr) ((Block) (BufferBlocks + ((Size) (bufHdr)->buf_id) * BLCKSZ))
#define BufferGetLSN(bufHdr) (PageGetLSN(BufHdrGetBlock(bufHdr)))
/* Note: this macro only works on local buffers, not shared ones! */
#define LocalBufHdrGetBlock(bufHdr) \
LocalBufferBlockPointers[-((bufHdr)->buf_id + 2)]
/* Bits in SyncOneBuffer's return value */
#define BUF_WRITTEN 0x01
#define BUF_REUSABLE 0x02
#define DROP_RELS_BSEARCH_THRESHOLD 20
typedef struct PrivateRefCountEntry
{
Buffer buffer;
int32 refcount;
} PrivateRefCountEntry;
/* 64 bytes, about the size of a cache line on common systems */
#define REFCOUNT_ARRAY_ENTRIES 8
/*
* Status of buffers to checkpoint for a particular tablespace, used
* internally in BufferSync.
*/
typedef struct CkptTsStatus
{
/* oid of the tablespace */
Oid tsId;
/*
* Checkpoint progress for this tablespace. To make progress comparable
* between tablespaces the progress is, for each tablespace, measured as a
* number between 0 and the total number of to-be-checkpointed pages. Each
* page checkpointed in this tablespace increments this space's progress
* by progress_slice.
*/
float8 progress;
float8 progress_slice;
/* number of to-be checkpointed pages in this tablespace */
int num_to_scan;
/* already processed pages in this tablespace */
int num_scanned;
/* current offset in CkptBufferIds for this tablespace */
int index;
} CkptTsStatus;
/* GUC variables */
bool zero_damaged_pages = false;
int bgwriter_lru_maxpages = 100;
double bgwriter_lru_multiplier = 2.0;
bool track_io_timing = false;
int effective_io_concurrency = 0;
/*
* GUC variables about triggering kernel writeback for buffers written; OS
* dependent defaults are set via the GUC mechanism.
*/
int checkpoint_flush_after = 0;
int bgwriter_flush_after = 0;
int backend_flush_after = 0;
/*
* How many buffers PrefetchBuffer callers should try to stay ahead of their
* ReadBuffer calls by. This is maintained by the assign hook for
* effective_io_concurrency. Zero means "never prefetch". This value is
* only used for buffers not belonging to tablespaces that have their
* effective_io_concurrency parameter set.
*/
int target_prefetch_pages = 0;
/* local state for StartBufferIO and related functions */
static BufferDesc *InProgressBuf = NULL;
static bool IsForInput;
/* local state for LockBufferForCleanup */
static BufferDesc *PinCountWaitBuf = NULL;
/*
* Backend-Private refcount management:
*
* Each buffer also has a private refcount that keeps track of the number of
* times the buffer is pinned in the current process. This is so that the
* shared refcount needs to be modified only once if a buffer is pinned more
* than once by an individual backend. It's also used to check that no buffers
* are still pinned at the end of transactions and when exiting.
*
*
* To avoid - as we used to - requiring an array with NBuffers entries to keep
* track of local buffers, we use a small sequentially searched array
* (PrivateRefCountArray) and an overflow hash table (PrivateRefCountHash) to
* keep track of backend local pins.
*
* Until no more than REFCOUNT_ARRAY_ENTRIES buffers are pinned at once, all
* refcounts are kept track of in the array; after that, new array entries
* displace old ones into the hash table. That way a frequently used entry
* can't get "stuck" in the hashtable while infrequent ones clog the array.
*
* Note that in most scenarios the number of pinned buffers will not exceed
* REFCOUNT_ARRAY_ENTRIES.
*
*
* To enter a buffer into the refcount tracking mechanism first reserve a free
* entry using ReservePrivateRefCountEntry() and then later, if necessary,
* fill it with NewPrivateRefCountEntry(). That split lets us avoid doing
* memory allocations in NewPrivateRefCountEntry() which can be important
* because in some scenarios it's called with a spinlock held...
*/
static struct PrivateRefCountEntry PrivateRefCountArray[REFCOUNT_ARRAY_ENTRIES];
static HTAB *PrivateRefCountHash = NULL;
static int32 PrivateRefCountOverflowed = 0;
static uint32 PrivateRefCountClock = 0;
static PrivateRefCountEntry *ReservedRefCountEntry = NULL;
static void ReservePrivateRefCountEntry(void);
static PrivateRefCountEntry *NewPrivateRefCountEntry(Buffer buffer);
static PrivateRefCountEntry *GetPrivateRefCountEntry(Buffer buffer, bool do_move);
static inline int32 GetPrivateRefCount(Buffer buffer);
static void ForgetPrivateRefCountEntry(PrivateRefCountEntry *ref);
/*
* Ensure that the PrivateRefCountArray has sufficient space to store one more
* entry. This has to be called before using NewPrivateRefCountEntry() to fill
* a new entry - but it's perfectly fine to not use a reserved entry.
*/
static void
ReservePrivateRefCountEntry(void)
{
/* Already reserved (or freed), nothing to do */
if (ReservedRefCountEntry != NULL)
return;
/*
* First search for a free entry the array, that'll be sufficient in the
* majority of cases.
*/
{
int i;
for (i = 0; i < REFCOUNT_ARRAY_ENTRIES; i++)
{
PrivateRefCountEntry *res;
res = &PrivateRefCountArray[i];
if (res->buffer == InvalidBuffer)
{
ReservedRefCountEntry = res;
return;
}
}
}
/*
* No luck. All array entries are full. Move one array entry into the hash
* table.
*/
{
/*
* Move entry from the current clock position in the array into the
* hashtable. Use that slot.
*/
PrivateRefCountEntry *hashent;
bool found;
/* select victim slot */
ReservedRefCountEntry =
&PrivateRefCountArray[PrivateRefCountClock++ % REFCOUNT_ARRAY_ENTRIES];
/* Better be used, otherwise we shouldn't get here. */
Assert(ReservedRefCountEntry->buffer != InvalidBuffer);
/* enter victim array entry into hashtable */
hashent = hash_search(PrivateRefCountHash,
(void *) &(ReservedRefCountEntry->buffer),
HASH_ENTER,
&found);
Assert(!found);
hashent->refcount = ReservedRefCountEntry->refcount;
/* clear the now free array slot */
ReservedRefCountEntry->buffer = InvalidBuffer;
ReservedRefCountEntry->refcount = 0;
PrivateRefCountOverflowed++;
}
}
/*
* Fill a previously reserved refcount entry.
*/
static PrivateRefCountEntry *
NewPrivateRefCountEntry(Buffer buffer)
{
PrivateRefCountEntry *res;
/* only allowed to be called when a reservation has been made */
Assert(ReservedRefCountEntry != NULL);
/* use up the reserved entry */
res = ReservedRefCountEntry;
ReservedRefCountEntry = NULL;
/* and fill it */
res->buffer = buffer;
res->refcount = 0;
return res;
}
/*
* Return the PrivateRefCount entry for the passed buffer.
*
* Returns NULL if a buffer doesn't have a refcount entry. Otherwise, if
* do_move is true, and the entry resides in the hashtable the entry is
* optimized for frequent access by moving it to the array.
*/
static PrivateRefCountEntry *
GetPrivateRefCountEntry(Buffer buffer, bool do_move)
{
PrivateRefCountEntry *res;
int i;
Assert(BufferIsValid(buffer));
Assert(!BufferIsLocal(buffer));
/*
* First search for references in the array, that'll be sufficient in the
* majority of cases.
*/
for (i = 0; i < REFCOUNT_ARRAY_ENTRIES; i++)
{
res = &PrivateRefCountArray[i];
if (res->buffer == buffer)
return res;
}
/*
* By here we know that the buffer, if already pinned, isn't residing in
* the array.
*
* Only look up the buffer in the hashtable if we've previously overflowed
* into it.
*/
if (PrivateRefCountOverflowed == 0)
return NULL;
res = hash_search(PrivateRefCountHash,
(void *) &buffer,
HASH_FIND,
NULL);
if (res == NULL)
return NULL;
else if (!do_move)
{
/* caller doesn't want us to move the hash entry into the array */
return res;
}
else
{
/* move buffer from hashtable into the free array slot */
bool found;
PrivateRefCountEntry *free;
/* Ensure there's a free array slot */
ReservePrivateRefCountEntry();
/* Use up the reserved slot */
Assert(ReservedRefCountEntry != NULL);
free = ReservedRefCountEntry;
ReservedRefCountEntry = NULL;
Assert(free->buffer == InvalidBuffer);
/* and fill it */
free->buffer = buffer;
free->refcount = res->refcount;
/* delete from hashtable */
hash_search(PrivateRefCountHash,
(void *) &buffer,
HASH_REMOVE,
&found);
Assert(found);
Assert(PrivateRefCountOverflowed > 0);
PrivateRefCountOverflowed--;
return free;
}
}
/*
* Returns how many times the passed buffer is pinned by this backend.
*
* Only works for shared memory buffers!
*/
static inline int32
GetPrivateRefCount(Buffer buffer)
{
PrivateRefCountEntry *ref;
Assert(BufferIsValid(buffer));
Assert(!BufferIsLocal(buffer));
/*
* Not moving the entry - that's ok for the current users, but we might
* want to change this one day.
*/
ref = GetPrivateRefCountEntry(buffer, false);
if (ref == NULL)
return 0;
return ref->refcount;
}
/*
* Release resources used to track the reference count of a buffer which we no
* longer have pinned and don't want to pin again immediately.
*/
static void
ForgetPrivateRefCountEntry(PrivateRefCountEntry *ref)
{
Assert(ref->refcount == 0);
if (ref >= &PrivateRefCountArray[0] &&
ref < &PrivateRefCountArray[REFCOUNT_ARRAY_ENTRIES])
{
ref->buffer = InvalidBuffer;
/*
* Mark the just used entry as reserved - in many scenarios that
* allows us to avoid ever having to search the array/hash for free
* entries.
*/
ReservedRefCountEntry = ref;
}
else
{
bool found;
Buffer buffer = ref->buffer;
hash_search(PrivateRefCountHash,
(void *) &buffer,
HASH_REMOVE,
&found);
Assert(found);
Assert(PrivateRefCountOverflowed > 0);
PrivateRefCountOverflowed--;
}
}
/*
* BufferIsPinned
* True iff the buffer is pinned (also checks for valid buffer number).
*
* NOTE: what we check here is that *this* backend holds a pin on
* the buffer. We do not care whether some other backend does.
*/
#define BufferIsPinned(bufnum) \
( \
!BufferIsValid(bufnum) ? \
false \
: \
BufferIsLocal(bufnum) ? \
(LocalRefCount[-(bufnum) - 1] > 0) \
: \
(GetPrivateRefCount(bufnum) > 0) \
)
static Buffer ReadBuffer_common(SMgrRelation reln, char relpersistence,
ForkNumber forkNum, BlockNumber blockNum,
ReadBufferMode mode, BufferAccessStrategy strategy,
bool *hit);
static bool PinBuffer(BufferDesc *buf, BufferAccessStrategy strategy);
static void PinBuffer_Locked(BufferDesc *buf);
static void UnpinBuffer(BufferDesc *buf, bool fixOwner);
static void BufferSync(int flags);
static uint32 WaitBufHdrUnlocked(BufferDesc *buf);
static int SyncOneBuffer(int buf_id, bool skip_recently_used, WritebackContext *flush_context);
static void WaitIO(BufferDesc *buf);
static bool StartBufferIO(BufferDesc *buf, bool forInput);
static void TerminateBufferIO(BufferDesc *buf, bool clear_dirty,
uint32 set_flag_bits);
static void shared_buffer_write_error_callback(void *arg);
static void local_buffer_write_error_callback(void *arg);
static BufferDesc *BufferAlloc(SMgrRelation smgr,
char relpersistence,
ForkNumber forkNum,
BlockNumber blockNum,
BufferAccessStrategy strategy,
bool *foundPtr);
static void FlushBuffer(BufferDesc *buf, SMgrRelation reln);
static void AtProcExit_Buffers(int code, Datum arg);
static void CheckForBufferLeaks(void);
static int rnode_comparator(const void *p1, const void *p2);
static int buffertag_comparator(const void *p1, const void *p2);
static int ckpt_buforder_comparator(const void *pa, const void *pb);
static int ts_ckpt_progress_comparator(Datum a, Datum b, void *arg);
#ifdef MPROTECT_BUFFERS
#define ShouldMemoryProtect(buf) (IsUnderPostmaster && \
IsNormalProcessingMode() && \
!BufferIsLocal(buf->buf_id+1) && \
!BufferIsInvalid(buf->buf_id+1))
static inline void BufferMProtect(volatile BufferDesc *bufHdr, int protectionLevel)
{
if (ShouldMemoryProtect(bufHdr))
{
if (mprotect(BufHdrGetBlock(bufHdr), BLCKSZ, protectionLevel))
{
ereport(ERROR,
(errmsg("unable to set memory level to %d, error %d, "
"block size %d, ptr %ld", protectionLevel,
errno, BLCKSZ, (long int) BufHdrGetBlock(bufHdr))));
}
}
}
#endif
static inline void ReleaseContentLock(volatile BufferDesc *buf)
{
LWLockRelease(BufferDescriptorGetContentLock(buf));
#ifdef MPROTECT_BUFFERS
/* make the buffer read-only after releasing content lock */
if (!LWLockHeldByMe(BufferDescriptorGetContentLock(buf)))
BufferMProtect(buf, PROT_READ);
#endif
}
static inline void AcquireContentLock(volatile BufferDesc *buf, LWLockMode mode)
{
#ifdef MPROTECT_BUFFERS
const bool newAcquisition =
!LWLockHeldByMe(BufferDescriptorGetContentLock(buf));
LWLockAcquire(BufferDescriptorGetContentLock(buf), mode);
/* new acquisition of content lock, allow read/write memory access */
if (newAcquisition)
BufferMProtect(buf, PROT_READ|PROT_WRITE);
#else
LWLockAcquire(BufferDescriptorGetContentLock(buf), mode);
#endif
}
static inline bool ConditionalAcquireContentLock(volatile BufferDesc *buf,
LWLockMode mode)
{
#ifdef MPROTECT_BUFFERS
const bool newAcquisition =
!LWLockHeldByMe(BufferDescriptorGetContentLock(buf));
if (LWLockConditionalAcquire(BufferDescriptorGetContentLock(buf), mode))
{
/* new acquisition of lock, allow read/write memory access */
if (newAcquisition)
BufferMProtect( buf, PROT_READ | PROT_WRITE );
return true;
}
return false;
#else
return LWLockConditionalAcquire(BufferDescriptorGetContentLock(buf), mode);
#endif
}
/*
* ComputeIoConcurrency -- get the number of pages to prefetch for a given
* number of spindles.
*/
bool
ComputeIoConcurrency(int io_concurrency, double *target)
{
double new_prefetch_pages = 0.0;
int i;
/*
* Make sure the io_concurrency value is within valid range; it may have
* been forced with a manual pg_tablespace update.
*/
io_concurrency = Min(Max(io_concurrency, 0), MAX_IO_CONCURRENCY);
/*----------
* The user-visible GUC parameter is the number of drives (spindles),
* which we need to translate to a number-of-pages-to-prefetch target.
* The target value is stashed in *extra and then assigned to the actual
* variable by assign_effective_io_concurrency.
*
* The expected number of prefetch pages needed to keep N drives busy is:
*
* drives | I/O requests
* -------+----------------
* 1 | 1
* 2 | 2/1 + 2/2 = 3
* 3 | 3/1 + 3/2 + 3/3 = 5 1/2
* 4 | 4/1 + 4/2 + 4/3 + 4/4 = 8 1/3
* n | n * H(n)
*
* This is called the "coupon collector problem" and H(n) is called the
* harmonic series. This could be approximated by n * ln(n), but for
* reasonable numbers of drives we might as well just compute the series.
*
* Alternatively we could set the target to the number of pages necessary
* so that the expected number of active spindles is some arbitrary
* percentage of the total. This sounds the same but is actually slightly
* different. The result ends up being ln(1-P)/ln((n-1)/n) where P is
* that desired fraction.
*
* Experimental results show that both of these formulas aren't aggressive
* enough, but we don't really have any better proposals.
*
* Note that if io_concurrency = 0 (disabled), we must set target = 0.
*----------
*/
for (i = 1; i <= io_concurrency; i++)
new_prefetch_pages += (double) io_concurrency / (double) i;
*target = new_prefetch_pages;
/* This range check shouldn't fail, but let's be paranoid */
return (new_prefetch_pages >= 0.0 && new_prefetch_pages < (double) INT_MAX);
}
/*
* PrefetchBuffer -- initiate asynchronous read of a block of a relation
*
* This is named by analogy to ReadBuffer but doesn't actually allocate a
* buffer. Instead it tries to ensure that a future ReadBuffer for the given
* block will not be delayed by the I/O. Prefetching is optional.
* No-op if prefetching isn't compiled in.
*/
void
PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum)
{
#ifdef USE_PREFETCH
Assert(RelationIsValid(reln));
Assert(BlockNumberIsValid(blockNum));
/* Open it at the smgr level if not already done */
RelationOpenSmgr(reln);
if (RelationUsesLocalBuffers(reln))
{
/* see comments in ReadBufferExtended */
if (RELATION_IS_OTHER_TEMP(reln))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions")));
/* pass it off to localbuf.c */
LocalPrefetchBuffer(reln->rd_smgr, forkNum, blockNum);
}
else
{
BufferTag newTag; /* identity of requested block */
uint32 newHash; /* hash value for newTag */
LWLock *newPartitionLock; /* buffer partition lock for it */
int buf_id;
/* create a tag so we can lookup the buffer */
INIT_BUFFERTAG(newTag, reln->rd_smgr->smgr_rnode.node,
forkNum, blockNum);
/* determine its hash code and partition lock ID */
newHash = BufTableHashCode(&newTag);
newPartitionLock = BufMappingPartitionLock(newHash);
/* see if the block is in the buffer pool already */
LWLockAcquire(newPartitionLock, LW_SHARED);
buf_id = BufTableLookup(&newTag, newHash);
LWLockRelease(newPartitionLock);
/* If not in buffers, initiate prefetch */
if (buf_id < 0)
smgrprefetch(reln->rd_smgr, forkNum, blockNum);
/*
* If the block *is* in buffers, we do nothing. This is not really
* ideal: the block might be just about to be evicted, which would be
* stupid since we know we are going to need it soon. But the only
* easy answer is to bump the usage_count, which does not seem like a
* great solution: when the caller does ultimately touch the block,
* usage_count would get bumped again, resulting in too much
* favoritism for blocks that are involved in a prefetch sequence. A
* real fix would involve some additional per-buffer state, and it's
* not clear that there's enough of a problem to justify that.
*/
}
#endif /* USE_PREFETCH */
}
/*
* ReadBuffer -- a shorthand for ReadBufferExtended, for reading from main
* fork with RBM_NORMAL mode and default strategy.
*/
Buffer
ReadBuffer(Relation reln, BlockNumber blockNum)
{
return ReadBufferExtended(reln, MAIN_FORKNUM, blockNum, RBM_NORMAL, NULL);
}
/*
* ReadBufferExtended -- returns a buffer containing the requested
* block of the requested relation. If the blknum
* requested is P_NEW, extend the relation file and
* allocate a new block. (Caller is responsible for
* ensuring that only one backend tries to extend a
* relation at the same time!)
*
* Returns: the buffer number for the buffer containing
* the block read. The returned buffer has been pinned.
* Does not return on error --- elog's instead.
*
* Assume when this function is called, that reln has been opened already.
*
* In RBM_NORMAL mode, the page is read from disk, and the page header is
* validated. An error is thrown if the page header is not valid. (But
* note that an all-zero page is considered "valid"; see PageIsVerified().)
*
* RBM_ZERO_ON_ERROR is like the normal mode, but if the page header is not
* valid, the page is zeroed instead of throwing an error. This is intended
* for non-critical data, where the caller is prepared to repair errors.
*
* In RBM_ZERO_AND_LOCK mode, if the page isn't in buffer cache already, it's
* filled with zeros instead of reading it from disk. Useful when the caller
* is going to fill the page from scratch, since this saves I/O and avoids
* unnecessary failure if the page-on-disk has corrupt page headers.
* The page is returned locked to ensure that the caller has a chance to
* initialize the page before it's made visible to others.
* Caution: do not use this mode to read a page that is beyond the relation's
* current physical EOF; that is likely to cause problems in md.c when
* the page is modified and written out. P_NEW is OK, though.
*
* RBM_ZERO_AND_CLEANUP_LOCK is the same as RBM_ZERO_AND_LOCK, but acquires
* a cleanup-strength lock on the page.
*
* RBM_NORMAL_NO_LOG mode is treated the same as RBM_NORMAL here.
*
* If strategy is not NULL, a nondefault buffer access strategy is used.
* See buffer/README for details.
*/
Buffer
ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
ReadBufferMode mode, BufferAccessStrategy strategy)
{
bool hit;
Buffer buf;
/* Open it at the smgr level if not already done */
RelationOpenSmgr(reln);
/*
* Reject attempts to read non-local temporary relations; we would be
* likely to get wrong data since we have no visibility into the owning
* session's local buffers.
*/
if (RelationUsesLocalBuffers(reln) && RELATION_IS_OTHER_TEMP(reln))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions")));
/*
* Read the buffer, and update pgstat counters to reflect a cache hit or
* miss.
*/
pgstat_count_buffer_read(reln);
buf = ReadBuffer_common(reln->rd_smgr, reln->rd_rel->relpersistence,
forkNum, blockNum, mode, strategy, &hit);
if (hit)
pgstat_count_buffer_hit(reln);
return buf;
}
/*
* ReadBufferWithoutRelcache -- like ReadBufferExtended, but doesn't require
* a relcache entry for the relation.
*
* NB: At present, this function may only be used on permanent relations, which
* is OK, because we only use it during XLOG replay. If in the future we
* want to use it on temporary or unlogged relations, we could pass additional
* parameters.
*/
Buffer
ReadBufferWithoutRelcache(RelFileNode rnode, ForkNumber forkNum,
BlockNumber blockNum, ReadBufferMode mode,
BufferAccessStrategy strategy)
{
bool hit;
/*
* Use default SMGR implementation when opening a relation backed by
* shared buffers
*/
SMgrRelation smgr = smgropen(rnode, InvalidBackendId, 0);
Assert(InRecovery);
return ReadBuffer_common(smgr, RELPERSISTENCE_PERMANENT, forkNum, blockNum,
mode, strategy, &hit);
}
/*
* ReadBuffer_common -- common logic for all ReadBuffer variants
*
* *hit is set to true if the request was satisfied from shared buffer cache.
*/
static Buffer
ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
BlockNumber blockNum, ReadBufferMode mode,
BufferAccessStrategy strategy, bool *hit)
{
BufferDesc *bufHdr;
Block bufBlock;
bool found;
bool isExtend;
/*
* Temp tables in Greenplum use shared buffers so that backends executing
* multiple slices of the same query can share them.
*/
bool isLocalBuf = false; /* SmgrIsTemp(smgr); */
*hit = false;
Assert(smgr != NULL);
/* Make sure we will have room to remember the buffer pin */
ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
isExtend = (blockNum == P_NEW);
TRACE_POSTGRESQL_BUFFER_READ_START(forkNum, blockNum,
smgr->smgr_rnode.node.spcNode,
smgr->smgr_rnode.node.dbNode,
smgr->smgr_rnode.node.relNode,
smgr->smgr_rnode.backend,
isExtend);
/* Substitute proper block number if caller asked for P_NEW */
if (isExtend)
blockNum = smgrnblocks(smgr, forkNum);
if (isLocalBuf)
{
bufHdr = LocalBufferAlloc(smgr, forkNum, blockNum, &found);
if (found)
pgBufferUsage.local_blks_hit++;
else if (isExtend)
pgBufferUsage.local_blks_written++;
else if (mode == RBM_NORMAL || mode == RBM_NORMAL_NO_LOG ||
mode == RBM_ZERO_ON_ERROR)
pgBufferUsage.local_blks_read++;
}
else
{
/*
* lookup the buffer. IO_IN_PROGRESS is set if the requested block is
* not currently in memory.
*/
bufHdr = BufferAlloc(smgr, relpersistence, forkNum, blockNum,
strategy, &found);
if (found)
pgBufferUsage.shared_blks_hit++;
else if (isExtend)
pgBufferUsage.shared_blks_written++;
else if (mode == RBM_NORMAL || mode == RBM_NORMAL_NO_LOG ||
mode == RBM_ZERO_ON_ERROR)
pgBufferUsage.shared_blks_read++;
}
/* At this point we do NOT hold any locks. */
/* if it was already in the buffer pool, we're done */
if (found)
{
if (!isExtend)
{
/* Just need to update stats before we exit */
*hit = true;
VacuumPageHit++;
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageHit;
TRACE_POSTGRESQL_BUFFER_READ_DONE(forkNum, blockNum,
smgr->smgr_rnode.node.spcNode,
smgr->smgr_rnode.node.dbNode,
smgr->smgr_rnode.node.relNode,
smgr->smgr_rnode.backend,
isExtend,
found);
/*
* In RBM_ZERO_AND_LOCK mode the caller expects the page to be
* locked on return.
*/
if (!isLocalBuf)
{
if (mode == RBM_ZERO_AND_LOCK)
AcquireContentLock(bufHdr,
LW_EXCLUSIVE);
else if (mode == RBM_ZERO_AND_CLEANUP_LOCK)
LockBufferForCleanup(BufferDescriptorGetBuffer(bufHdr));
}
return BufferDescriptorGetBuffer(bufHdr);
}
/*
* We get here only in the corner case where we are trying to extend
* the relation but we found a pre-existing buffer marked BM_VALID.
* This can happen because mdread doesn't complain about reads beyond
* EOF (when zero_damaged_pages is ON) and so a previous attempt to
* read a block beyond EOF could have left a "valid" zero-filled
* buffer. Unfortunately, we have also seen this case occurring
* because of buggy Linux kernels that sometimes return an
* lseek(SEEK_END) result that doesn't account for a recent write. In
* that situation, the pre-existing buffer would contain valid data
* that we don't want to overwrite. Since the legitimate case should
* always have left a zero-filled buffer, complain if not PageIsNew.
*/
bufBlock = isLocalBuf ? LocalBufHdrGetBlock(bufHdr) : BufHdrGetBlock(bufHdr);
if (!PageIsNew((Page) bufBlock))
ereport(ERROR,
(errmsg("unexpected data beyond EOF in block %u of relation %s",
blockNum, relpath(smgr->smgr_rnode, forkNum)),
errhint("This has been seen to occur with buggy kernels; consider updating your system.")));
/*
* We *must* do smgrextend before succeeding, else the page will not
* be reserved by the kernel, and the next P_NEW call will decide to
* return the same page. Clear the BM_VALID bit, do the StartBufferIO
* call that BufferAlloc didn't, and proceed.
*/
if (isLocalBuf)
{
/* Only need to adjust flags */
uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
Assert(buf_state & BM_VALID);
buf_state &= ~BM_VALID;
pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
}
else
{
/*
* Loop to handle the very small possibility that someone re-sets
* BM_VALID between our clearing it and StartBufferIO inspecting
* it.
*/
do
{
uint32 buf_state = LockBufHdr(bufHdr);
Assert(buf_state & BM_VALID);
buf_state &= ~BM_VALID;
UnlockBufHdr(bufHdr, buf_state);
} while (!StartBufferIO(bufHdr, true));
}
}
/*
* if we have gotten to this point, we have allocated a buffer for the
* page but its contents are not yet valid. IO_IN_PROGRESS is set for it,
* if it's a shared buffer.
*
* Note: if smgrextend fails, we will end up with a buffer that is
* allocated but not marked BM_VALID. P_NEW will still select the same
* block number (because the relation didn't get any longer on disk) and
* so future attempts to extend the relation will find the same buffer (if
* it's not been recycled) but come right back here to try smgrextend
* again.
*/
Assert(!(pg_atomic_read_u32(&bufHdr->state) & BM_VALID)); /* spinlock not needed */
bufBlock = isLocalBuf ? LocalBufHdrGetBlock(bufHdr) : BufHdrGetBlock(bufHdr);
#ifdef MPROTECT_BUFFERS
BufferMProtect(bufHdr, PROT_WRITE | PROT_READ);
#endif
if (isExtend)
{
/* new buffers are zero-filled */
MemSet((char *) bufBlock, 0, BLCKSZ);
/* don't set checksum for all-zero page */
smgrextend(smgr, forkNum, blockNum, (char *) bufBlock, false);
/*
* NB: we're *not* doing a ScheduleBufferTagForWriteback here;
* although we're essentially performing a write. At least on linux
* doing so defeats the 'delayed allocation' mechanism, leading to
* increased file fragmentation.
*/
}
else
{
/*
* Read in the page, unless the caller intends to overwrite it and
* just wants us to allocate a buffer.
*/
if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
MemSet((char *) bufBlock, 0, BLCKSZ);
else
{
instr_time io_start,
io_time;
if (track_io_timing)
INSTR_TIME_SET_CURRENT(io_start);
smgrread(smgr, forkNum, blockNum, (char *) bufBlock);
if (track_io_timing)
{
INSTR_TIME_SET_CURRENT(io_time);
INSTR_TIME_SUBTRACT(io_time, io_start);
pgstat_count_buffer_read_time(INSTR_TIME_GET_MICROSEC(io_time));
INSTR_TIME_ADD(pgBufferUsage.blk_read_time, io_time);
}
/* check for garbage data */
if (!PageIsVerified((Page) bufBlock, blockNum))
{
if (mode == RBM_ZERO_ON_ERROR || zero_damaged_pages)
{
ereport(WARNING,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("invalid page in block %u of relation %s; zeroing out page",
blockNum,
relpath(smgr->smgr_rnode, forkNum))));
MemSet((char *) bufBlock, 0, BLCKSZ);
}
else
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("invalid page in block %u of relation %s",
blockNum,
relpath(smgr->smgr_rnode, forkNum))));
}
}
}
#ifdef MPROTECT_BUFFERS
BufferMProtect( bufHdr, PROT_READ );
#endif
/*
* In RBM_ZERO_AND_LOCK mode, grab the buffer content lock before marking
* the page as valid, to make sure that no other backend sees the zeroed
* page before the caller has had a chance to initialize it.
*
* Since no-one else can be looking at the page contents yet, there is no
* difference between an exclusive lock and a cleanup-strength lock. (Note
* that we cannot use LockBuffer() or LockBufferForCleanup() here, because
* they assert that the buffer is already valid.)
*/
if ((mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK) &&
!isLocalBuf)
{
AcquireContentLock(bufHdr, LW_EXCLUSIVE);
}
if (isLocalBuf)
{
/* Only need to adjust flags */
uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
buf_state |= BM_VALID;
pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
}
else
{
/* Set BM_VALID, terminate IO, and wake up any waiters */
TerminateBufferIO(bufHdr, false, BM_VALID);
}
VacuumPageMiss++;
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageMiss;
TRACE_POSTGRESQL_BUFFER_READ_DONE(forkNum, blockNum,
smgr->smgr_rnode.node.spcNode,
smgr->smgr_rnode.node.dbNode,
smgr->smgr_rnode.node.relNode,
smgr->smgr_rnode.backend,
isExtend,
found);
return BufferDescriptorGetBuffer(bufHdr);
}
/*
* BufferAlloc -- subroutine for ReadBuffer. Handles lookup of a shared
* buffer. If no buffer exists already, selects a replacement
* victim and evicts the old page, but does NOT read in new page.
*
* "strategy" can be a buffer replacement strategy object, or NULL for
* the default strategy. The selected buffer's usage_count is advanced when
* using the default strategy, but otherwise possibly not (see PinBuffer).
*
* The returned buffer is pinned and is already marked as holding the
* desired page. If it already did have the desired page, *foundPtr is
* set true. Otherwise, *foundPtr is set false and the buffer is marked
* as IO_IN_PROGRESS; ReadBuffer will now need to do I/O to fill it.
*
* *foundPtr is actually redundant with the buffer's BM_VALID flag, but
* we keep it for simplicity in ReadBuffer.
*
* No locks are held either at entry or exit.
*/
static BufferDesc *
BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
BlockNumber blockNum,
BufferAccessStrategy strategy,
bool *foundPtr)
{
BufferTag newTag; /* identity of requested block */
uint32 newHash; /* hash value for newTag */
LWLock *newPartitionLock; /* buffer partition lock for it */
BufferTag oldTag; /* previous identity of selected buffer */
uint32 oldHash; /* hash value for oldTag */
LWLock *oldPartitionLock; /* buffer partition lock for it */
uint32 oldFlags;
int buf_id;
BufferDesc *buf;
bool valid;
uint32 buf_state;
/* create a tag so we can lookup the buffer */
INIT_BUFFERTAG(newTag, smgr->smgr_rnode.node, forkNum, blockNum);
/* determine its hash code and partition lock ID */
newHash = BufTableHashCode(&newTag);
newPartitionLock = BufMappingPartitionLock(newHash);
/* see if the block is in the buffer pool already */
LWLockAcquire(newPartitionLock, LW_SHARED);
buf_id = BufTableLookup(&newTag, newHash);
if (buf_id >= 0)
{
/*
* Found it. Now, pin the buffer so no one can steal it from the
* buffer pool, and check to see if the correct data has been loaded
* into the buffer.
*/
buf = GetBufferDescriptor(buf_id);
valid = PinBuffer(buf, strategy);
/* Can release the mapping lock as soon as we've pinned it */
LWLockRelease(newPartitionLock);
*foundPtr = true;
if (!valid)
{
/*
* We can only get here if (a) someone else is still reading in
* the page, or (b) a previous read attempt failed. We have to
* wait for any active read attempt to finish, and then set up our
* own read attempt if the page is still not BM_VALID.
* StartBufferIO does it all.
*/
if (StartBufferIO(buf, true))
{
/*
* If we get here, previous attempts to read the buffer must
* have failed ... but we shall bravely try again.
*/
*foundPtr = false;
}
}
return buf;
}
/*
* Didn't find it in the buffer pool. We'll have to initialize a new
* buffer. Remember to unlock the mapping lock while doing the work.
*/
LWLockRelease(newPartitionLock);
/* Loop here in case we have to try another victim buffer */
for (;;)
{
/*
* Ensure, while the spinlock's not yet held, that there's a free
* refcount entry.
*/
ReservePrivateRefCountEntry();
/*
* Select a victim buffer. The buffer is returned with its header
* spinlock still held!
*/
buf = StrategyGetBuffer(strategy, &buf_state);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) == 0);
/* Must copy buffer flags while we still hold the spinlock */
oldFlags = buf_state & BUF_FLAG_MASK;
/* Pin the buffer and then release the buffer spinlock */
PinBuffer_Locked(buf);
/*
* If the buffer was dirty, try to write it out. There is a race
* condition here, in that someone might dirty it after we released it
* above, or even while we are writing it out (since our share-lock
* won't prevent hint-bit updates). We will recheck the dirty bit
* after re-locking the buffer header.
*/
if (oldFlags & BM_DIRTY)
{
/*
* We need a share-lock on the buffer contents to write it out
* (else we might write invalid data, eg because someone else is
* compacting the page contents while we write). We must use a
* conditional lock acquisition here to avoid deadlock. Even
* though the buffer was not pinned (and therefore surely not
* locked) when StrategyGetBuffer returned it, someone else could
* have pinned and exclusive-locked it by the time we get here. If
* we try to get the lock unconditionally, we'd block waiting for
* them; if they later block waiting for us, deadlock ensues.
* (This has been observed to happen when two backends are both
* trying to split btree index pages, and the second one just
* happens to be trying to split the page the first one got from
* StrategyGetBuffer.)
*/
if (ConditionalAcquireContentLock(buf, LW_SHARED))
{
/*
* If using a nondefault strategy, and writing the buffer
* would require a WAL flush, let the strategy decide whether
* to go ahead and write/reuse the buffer or to choose another
* victim. We need lock to inspect the page LSN, so this
* can't be done inside StrategyGetBuffer.
*/
if (strategy != NULL)
{
XLogRecPtr lsn;
/* Read the LSN while holding buffer header lock */
buf_state = LockBufHdr(buf);
lsn = BufferGetLSN(buf);
UnlockBufHdr(buf, buf_state);
if (XLogNeedsFlush(lsn) &&
StrategyRejectBuffer(strategy, buf))
{
/* Drop lock/pin and loop around for another buffer */
ReleaseContentLock(buf);
UnpinBuffer(buf, true);
continue;
}
}
/* OK, do the I/O */
TRACE_POSTGRESQL_BUFFER_WRITE_DIRTY_START(forkNum, blockNum,
smgr->smgr_rnode.node.spcNode,
smgr->smgr_rnode.node.dbNode,
smgr->smgr_rnode.node.relNode);
FlushBuffer(buf, NULL);
ReleaseContentLock(buf);
ScheduleBufferTagForWriteback(&BackendWritebackContext,
&buf->tag);
TRACE_POSTGRESQL_BUFFER_WRITE_DIRTY_DONE(forkNum, blockNum,
smgr->smgr_rnode.node.spcNode,
smgr->smgr_rnode.node.dbNode,
smgr->smgr_rnode.node.relNode);
}
else
{
/*
* Someone else has locked the buffer, so give it up and loop
* back to get another one.
*/
UnpinBuffer(buf, true);
continue;
}
}
/*
* To change the association of a valid buffer, we'll need to have
* exclusive lock on both the old and new mapping partitions.
*/
if (oldFlags & BM_TAG_VALID)
{
/*
* Need to compute the old tag's hashcode and partition lock ID.
* XXX is it worth storing the hashcode in BufferDesc so we need
* not recompute it here? Probably not.
*/
oldTag = buf->tag;
oldHash = BufTableHashCode(&oldTag);
oldPartitionLock = BufMappingPartitionLock(oldHash);
/*
* Must lock the lower-numbered partition first to avoid
* deadlocks.
*/
if (oldPartitionLock < newPartitionLock)
{
LWLockAcquire(oldPartitionLock, LW_EXCLUSIVE);
LWLockAcquire(newPartitionLock, LW_EXCLUSIVE);
}
else if (oldPartitionLock > newPartitionLock)
{
LWLockAcquire(newPartitionLock, LW_EXCLUSIVE);
LWLockAcquire(oldPartitionLock, LW_EXCLUSIVE);
}
else
{
/* only one partition, only one lock */
LWLockAcquire(newPartitionLock, LW_EXCLUSIVE);
}
}
else
{
/* if it wasn't valid, we need only the new partition */
LWLockAcquire(newPartitionLock, LW_EXCLUSIVE);
/* remember we have no old-partition lock or tag */
oldPartitionLock = NULL;
/* this just keeps the compiler quiet about uninit variables */
oldHash = 0;
}
/*
* Try to make a hashtable entry for the buffer under its new tag.
* This could fail because while we were writing someone else
* allocated another buffer for the same block we want to read in.
* Note that we have not yet removed the hashtable entry for the old
* tag.
*/
buf_id = BufTableInsert(&newTag, newHash, buf->buf_id);
if (buf_id >= 0)
{
/*
* Got a collision. Someone has already done what we were about to
* do. We'll just handle this as if it were found in the buffer
* pool in the first place. First, give up the buffer we were
* planning to use.
*/
UnpinBuffer(buf, true);
/* Can give up that buffer's mapping partition lock now */
if (oldPartitionLock != NULL &&
oldPartitionLock != newPartitionLock)
LWLockRelease(oldPartitionLock);
/* remaining code should match code at top of routine */
buf = GetBufferDescriptor(buf_id);
valid = PinBuffer(buf, strategy);
/* Can release the mapping lock as soon as we've pinned it */
LWLockRelease(newPartitionLock);
*foundPtr = true;
if (!valid)
{
/*
* We can only get here if (a) someone else is still reading
* in the page, or (b) a previous read attempt failed. We
* have to wait for any active read attempt to finish, and
* then set up our own read attempt if the page is still not
* BM_VALID. StartBufferIO does it all.
*/
if (StartBufferIO(buf, true))
{
/*
* If we get here, previous attempts to read the buffer
* must have failed ... but we shall bravely try again.
*/
*foundPtr = false;
}
}
return buf;
}
/*
* Need to lock the buffer header too in order to change its tag.
*/
buf_state = LockBufHdr(buf);
/*
* Somebody could have pinned or re-dirtied the buffer while we were
* doing the I/O and making the new hashtable entry. If so, we can't
* recycle this buffer; we must undo everything we've done and start
* over with a new victim buffer.
*/
oldFlags = buf_state & BUF_FLAG_MASK;
if (BUF_STATE_GET_REFCOUNT(buf_state) == 1 && !(oldFlags & BM_DIRTY))
break;
UnlockBufHdr(buf, buf_state);
BufTableDelete(&newTag, newHash);
if (oldPartitionLock != NULL &&
oldPartitionLock != newPartitionLock)
LWLockRelease(oldPartitionLock);
LWLockRelease(newPartitionLock);
UnpinBuffer(buf, true);
}
/*
* Okay, it's finally safe to rename the buffer.
*
* Clearing BM_VALID here is necessary, clearing the dirtybits is just
* paranoia. We also reset the usage_count since any recency of use of
* the old content is no longer relevant. (The usage_count starts out at
* 1 so that the buffer can survive one clock-sweep pass.)
*
* Make sure BM_PERMANENT is set for buffers that must be written at every
* checkpoint. Unlogged buffers only need to be written at shutdown
* checkpoints, except for their "init" forks, which need to be treated
* just like permanent relations.
*/
buf->tag = newTag;
buf_state &= ~(BM_VALID | BM_DIRTY | BM_JUST_DIRTIED |
BM_CHECKPOINT_NEEDED | BM_IO_ERROR | BM_PERMANENT |
BM_TEMP |
BUF_USAGECOUNT_MASK);
if (relpersistence == RELPERSISTENCE_PERMANENT || forkNum == INIT_FORKNUM)
buf_state |= BM_TAG_VALID | BM_PERMANENT | BUF_USAGECOUNT_ONE;
else if (relpersistence == RELPERSISTENCE_TEMP)
buf_state |= BM_TAG_VALID | BM_TEMP | BUF_USAGECOUNT_ONE;
else
buf_state |= BM_TAG_VALID | BUF_USAGECOUNT_ONE;
UnlockBufHdr(buf, buf_state);
if (oldPartitionLock != NULL)
{
BufTableDelete(&oldTag, oldHash);
if (oldPartitionLock != newPartitionLock)
LWLockRelease(oldPartitionLock);
}
LWLockRelease(newPartitionLock);
/*
* Buffer contents are currently invalid. Try to get the io_in_progress
* lock. If StartBufferIO returns false, then someone else managed to
* read it before we did, so there's nothing left for BufferAlloc() to do.
*/
if (StartBufferIO(buf, true))
*foundPtr = false;
else
*foundPtr = true;
return buf;
}
/*
* InvalidateBuffer -- mark a shared buffer invalid and return it to the
* freelist.
*
* The buffer header spinlock must be held at entry. We drop it before
* returning. (This is sane because the caller must have locked the
* buffer in order to be sure it should be dropped.)
*
* This is used only in contexts such as dropping a relation. We assume
* that no other backend could possibly be interested in using the page,
* so the only reason the buffer might be pinned is if someone else is
* trying to write it out. We have to let them finish before we can
* reclaim the buffer.
*
* The buffer could get reclaimed by someone else while we are waiting
* to acquire the necessary locks; if so, don't mess it up.
*/
static void
InvalidateBuffer(BufferDesc *buf)
{
BufferTag oldTag;
uint32 oldHash; /* hash value for oldTag */
LWLock *oldPartitionLock; /* buffer partition lock for it */
uint32 oldFlags;
uint32 buf_state;
/* Save the original buffer tag before dropping the spinlock */
oldTag = buf->tag;
buf_state = pg_atomic_read_u32(&buf->state);
Assert(buf_state & BM_LOCKED);
UnlockBufHdr(buf, buf_state);
/*
* Need to compute the old tag's hashcode and partition lock ID. XXX is it
* worth storing the hashcode in BufferDesc so we need not recompute it
* here? Probably not.
*/
oldHash = BufTableHashCode(&oldTag);
oldPartitionLock = BufMappingPartitionLock(oldHash);
retry:
/*
* Acquire exclusive mapping lock in preparation for changing the buffer's
* association.
*/
LWLockAcquire(oldPartitionLock, LW_EXCLUSIVE);
/* Re-lock the buffer header */
buf_state = LockBufHdr(buf);
/* If it's changed while we were waiting for lock, do nothing */
if (!BUFFERTAGS_EQUAL(buf->tag, oldTag))
{
UnlockBufHdr(buf, buf_state);
LWLockRelease(oldPartitionLock);
return;
}
/*
* We assume the only reason for it to be pinned is that someone else is
* flushing the page out. Wait for them to finish. (This could be an
* infinite loop if the refcount is messed up... it would be nice to time
* out after awhile, but there seems no way to be sure how many loops may
* be needed. Note that if the other guy has pinned the buffer but not
* yet done StartBufferIO, WaitIO will fall through and we'll effectively
* be busy-looping here.)
*/
if (BUF_STATE_GET_REFCOUNT(buf_state) != 0)
{
UnlockBufHdr(buf, buf_state);
LWLockRelease(oldPartitionLock);
/* safety check: should definitely not be our *own* pin */
if (GetPrivateRefCount(BufferDescriptorGetBuffer(buf)) > 0)
elog(ERROR, "buffer is pinned in InvalidateBuffer");
WaitIO(buf);
goto retry;
}
/*
* Clear out the buffer's tag and flags. We must do this to ensure that
* linear scans of the buffer array don't think the buffer is valid.
*/
oldFlags = buf_state & BUF_FLAG_MASK;
CLEAR_BUFFERTAG(buf->tag);
buf_state &= ~(BUF_FLAG_MASK | BUF_USAGECOUNT_MASK);
UnlockBufHdr(buf, buf_state);
/*
* Remove the buffer from the lookup hashtable, if it was in there.
*/
if (oldFlags & BM_TAG_VALID)
BufTableDelete(&oldTag, oldHash);
/*
* Done with mapping lock.
*/
LWLockRelease(oldPartitionLock);
/*
* Insert the buffer at the head of the list of free buffers.
*/
StrategyFreeBuffer(buf);
}
/*
* MarkBufferDirty
*
* Marks buffer contents as dirty (actual write happens later).
*
* Buffer must be pinned and exclusive-locked. (If caller does not hold
* exclusive lock, then somebody could be in process of writing the buffer,
* leading to risk of bad data written to disk.)
*/
void
MarkBufferDirty(Buffer buffer)
{
BufferDesc *bufHdr;
uint32 buf_state;
uint32 old_buf_state;
if (!BufferIsValid(buffer))
elog(ERROR, "bad buffer ID: %d", buffer);
if (BufferIsLocal(buffer))
{
MarkLocalBufferDirty(buffer);
return;
}
bufHdr = GetBufferDescriptor(buffer - 1);
Assert(BufferIsPinned(buffer));
Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
LW_EXCLUSIVE));
old_buf_state = pg_atomic_read_u32(&bufHdr->state);
for (;;)
{
if (old_buf_state & BM_LOCKED)
old_buf_state = WaitBufHdrUnlocked(bufHdr);
buf_state = old_buf_state;
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
buf_state |= BM_DIRTY | BM_JUST_DIRTIED;
if (pg_atomic_compare_exchange_u32(&bufHdr->state, &old_buf_state,
buf_state))
break;
}
/*
* If the buffer was not dirty already, do vacuum accounting.
*/
if (!(old_buf_state & BM_DIRTY))
{
VacuumPageDirty++;
pgBufferUsage.shared_blks_dirtied++;
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageDirty;
}
}
/*
* ReleaseAndReadBuffer -- combine ReleaseBuffer() and ReadBuffer()
*
* Formerly, this saved one cycle of acquiring/releasing the BufMgrLock
* compared to calling the two routines separately. Now it's mainly just
* a convenience function. However, if the passed buffer is valid and
* already contains the desired block, we just return it as-is; and that
* does save considerable work compared to a full release and reacquire.
*
* Note: it is OK to pass buffer == InvalidBuffer, indicating that no old
* buffer actually needs to be released. This case is the same as ReadBuffer,
* but can save some tests in the caller.
*/
Buffer
ReleaseAndReadBuffer(Buffer buffer,
Relation relation,
BlockNumber blockNum)
{
ForkNumber forkNum = MAIN_FORKNUM;
BufferDesc *bufHdr;
if (BufferIsValid(buffer))
{
Assert(BufferIsPinned(buffer));
if (BufferIsLocal(buffer))
{
bufHdr = GetLocalBufferDescriptor(-buffer - 1);
if (bufHdr->tag.blockNum == blockNum &&
RelFileNodeEquals(bufHdr->tag.rnode, relation->rd_node) &&
bufHdr->tag.forkNum == forkNum)
return buffer;
ResourceOwnerForgetBuffer(CurrentResourceOwner, buffer);
LocalRefCount[-buffer - 1]--;
}
else
{
bufHdr = GetBufferDescriptor(buffer - 1);
/* we have pin, so it's ok to examine tag without spinlock */
if (bufHdr->tag.blockNum == blockNum &&
RelFileNodeEquals(bufHdr->tag.rnode, relation->rd_node) &&
bufHdr->tag.forkNum == forkNum)
return buffer;
UnpinBuffer(bufHdr, true);
}
}
return ReadBuffer(relation, blockNum);
}
/*
* PinBuffer -- make buffer unavailable for replacement.
*
* For the default access strategy, the buffer's usage_count is incremented
* when we first pin it; for other strategies we just make sure the usage_count
* isn't zero. (The idea of the latter is that we don't want synchronized
* heap scans to inflate the count, but we need it to not be zero to discourage
* other backends from stealing buffers from our ring. As long as we cycle
* through the ring faster than the global clock-sweep cycles, buffers in
* our ring won't be chosen as victims for replacement by other backends.)
*
* This should be applied only to shared buffers, never local ones.
*
* Since buffers are pinned/unpinned very frequently, pin buffers without
* taking the buffer header lock; instead update the state variable in loop of
* CAS operations. Hopefully it's just a single CAS.
*
* Note that ResourceOwnerEnlargeBuffers must have been done already.
*
* Returns true if buffer is BM_VALID, else false. This provision allows
* some callers to avoid an extra spinlock cycle.
*/
static bool
PinBuffer(BufferDesc *buf, BufferAccessStrategy strategy)
{
Buffer b = BufferDescriptorGetBuffer(buf);
bool result;
PrivateRefCountEntry *ref;
ref = GetPrivateRefCountEntry(b, true);
if (ref == NULL)
{
uint32 buf_state;
uint32 old_buf_state;
ReservePrivateRefCountEntry();
ref = NewPrivateRefCountEntry(b);
old_buf_state = pg_atomic_read_u32(&buf->state);
for (;;)
{
if (old_buf_state & BM_LOCKED)
old_buf_state = WaitBufHdrUnlocked(buf);
buf_state = old_buf_state;
/* increase refcount */
buf_state += BUF_REFCOUNT_ONE;
if (strategy == NULL)
{
/* Default case: increase usagecount unless already max. */
if (BUF_STATE_GET_USAGECOUNT(buf_state) < BM_MAX_USAGE_COUNT)
buf_state += BUF_USAGECOUNT_ONE;
}
else
{
/*
* Ring buffers shouldn't evict others from pool. Thus we
* don't make usagecount more than 1.
*/
if (BUF_STATE_GET_USAGECOUNT(buf_state) == 0)
buf_state += BUF_USAGECOUNT_ONE;
}
if (pg_atomic_compare_exchange_u32(&buf->state, &old_buf_state,
buf_state))
{
result = (buf_state & BM_VALID) != 0;
break;
}
}
#ifdef MPROTECT_BUFFERS
BufferMProtect(buf, PROT_READ);
#endif
}
else
{
/* If we previously pinned the buffer, it must surely be valid */
result = true;
}
ref->refcount++;
Assert(ref->refcount > 0);
ResourceOwnerRememberBuffer(CurrentResourceOwner, b);
return result;
}
/*
* PinBuffer_Locked -- as above, but caller already locked the buffer header.
* The spinlock is released before return.
*
* As this function is called with the spinlock held, the caller has to
* previously call ReservePrivateRefCountEntry().
*
* Currently, no callers of this function want to modify the buffer's
* usage_count at all, so there's no need for a strategy parameter.
* Also we don't bother with a BM_VALID test (the caller could check that for
* itself).
*
* Also all callers only ever use this function when it's known that the
* buffer can't have a preexisting pin by this backend. That allows us to skip
* searching the private refcount array & hash, which is a boon, because the
* spinlock is still held.
*
* Note: use of this routine is frequently mandatory, not just an optimization
* to save a spin lock/unlock cycle, because we need to pin a buffer before
* its state can change under us.
*/
static void
PinBuffer_Locked(BufferDesc *buf)
{
Buffer b;
PrivateRefCountEntry *ref;
uint32 buf_state;
/*
* As explained, We don't expect any preexisting pins. That allows us to
* manipulate the PrivateRefCount after releasing the spinlock
*/
Assert(GetPrivateRefCountEntry(BufferDescriptorGetBuffer(buf), false) == NULL);
/*
* Since we hold the buffer spinlock, we can update the buffer state and
* release the lock in one operation.
*/
buf_state = pg_atomic_read_u32(&buf->state);
Assert(buf_state & BM_LOCKED);
buf_state += BUF_REFCOUNT_ONE;
UnlockBufHdr(buf, buf_state);
#ifdef MPROTECT_BUFFERS
BufferMProtect(buf, PROT_READ);
#endif
b = BufferDescriptorGetBuffer(buf);
ref = NewPrivateRefCountEntry(b);
ref->refcount++;
ResourceOwnerRememberBuffer(CurrentResourceOwner, b);
}
/*
* UnpinBuffer -- make buffer available for replacement.
*
* This should be applied only to shared buffers, never local ones.
*
* Most but not all callers want CurrentResourceOwner to be adjusted.
* Those that don't should pass fixOwner = false.
*/
static void
UnpinBuffer(BufferDesc *buf, bool fixOwner)
{
PrivateRefCountEntry *ref;
Buffer b = BufferDescriptorGetBuffer(buf);
/* not moving as we're likely deleting it soon anyway */
ref = GetPrivateRefCountEntry(b, false);
Assert(ref != NULL);
if (fixOwner)
ResourceOwnerForgetBuffer(CurrentResourceOwner, b);
Assert(ref->refcount > 0);
ref->refcount--;
if (ref->refcount == 0)
{
uint32 buf_state;
uint32 old_buf_state;
/* I'd better not still hold any locks on the buffer */
Assert(!LWLockHeldByMe(BufferDescriptorGetContentLock(buf)));
Assert(!LWLockHeldByMe(BufferDescriptorGetIOLock(buf)));
/*
* Decrement the shared reference count.
*
* Since buffer spinlock holder can update status using just write,
* it's not safe to use atomic decrement here; thus use a CAS loop.
*/
old_buf_state = pg_atomic_read_u32(&buf->state);
for (;;)
{
if (old_buf_state & BM_LOCKED)
old_buf_state = WaitBufHdrUnlocked(buf);
buf_state = old_buf_state;
buf_state -= BUF_REFCOUNT_ONE;
if (pg_atomic_compare_exchange_u32(&buf->state, &old_buf_state,
buf_state))
break;
}
#ifdef MPROTECT_BUFFERS
BufferMProtect(buf, PROT_NONE);
#endif
/* Support LockBufferForCleanup() */
if (buf_state & BM_PIN_COUNT_WAITER)
{
/*
* Acquire the buffer header lock, re-check that there's a waiter.
* Another backend could have unpinned this buffer, and already
* woken up the waiter. There's no danger of the buffer being
* replaced after we unpinned it above, as it's pinned by the
* waiter.
*/
buf_state = LockBufHdr(buf);
if ((buf_state & BM_PIN_COUNT_WAITER) &&
BUF_STATE_GET_REFCOUNT(buf_state) == 1)
{
/* we just released the last pin other than the waiter's */
int wait_backend_pid = buf->wait_backend_pid;
buf_state &= ~BM_PIN_COUNT_WAITER;
UnlockBufHdr(buf, buf_state);
ProcSendSignal(wait_backend_pid);
}
else
UnlockBufHdr(buf, buf_state);
}
ForgetPrivateRefCountEntry(ref);
}
}
/*
* BufferSync -- Write out all dirty buffers in the pool.
*
* This is called at checkpoint time to write out all dirty shared buffers.
* The checkpoint request flags should be passed in. If CHECKPOINT_IMMEDIATE
* is set, we disable delays between writes; if CHECKPOINT_IS_SHUTDOWN,
* CHECKPOINT_END_OF_RECOVERY or CHECKPOINT_FLUSH_ALL is set, we write even
* unlogged buffers, which are otherwise skipped. The remaining flags
* currently have no effect here.
*/
static void
BufferSync(int flags)
{
uint32 buf_state;
int buf_id;
int num_to_scan;
int num_spaces;
int num_processed;
int num_written;
CkptTsStatus *per_ts_stat = NULL;
Oid last_tsid;
binaryheap *ts_heap;
int i;
int mask = BM_DIRTY;
WritebackContext wb_context;
/* Make sure we can handle the pin inside SyncOneBuffer */
ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
/*
* Unless this is a shutdown checkpoint or we have been explicitly told,
* we write only permanent, dirty buffers. But at shutdown or end of
* recovery, we write all dirty buffers.
*/
if (!((flags & (CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_END_OF_RECOVERY |
CHECKPOINT_FLUSH_ALL))))
mask |= BM_PERMANENT;
/*
* Loop over all buffers, and mark the ones that need to be written with
* BM_CHECKPOINT_NEEDED. Count them as we go (num_to_scan), so that we
* can estimate how much work needs to be done.
*
* This allows us to write only those pages that were dirty when the
* checkpoint began, and not those that get dirtied while it proceeds.
* Whenever a page with BM_CHECKPOINT_NEEDED is written out, either by us
* later in this function, or by normal backends or the bgwriter cleaning
* scan, the flag is cleared. Any buffer dirtied after this point won't
* have the flag set.
*
* Note that if we fail to write some buffer, we may leave buffers with
* BM_CHECKPOINT_NEEDED still set. This is OK since any such buffer would
* certainly need to be written for the next checkpoint attempt, too.
*/
num_to_scan = 0;
for (buf_id = 0; buf_id < NBuffers; buf_id++)
{
BufferDesc *bufHdr = GetBufferDescriptor(buf_id);
/*
* Header spinlock is enough to examine BM_DIRTY, see comment in
* SyncOneBuffer.
*/
buf_state = LockBufHdr(bufHdr);
/*
* Temp tables in Greenplum use shared buffers. Filter buffers
* belonging to temp tables out during checkpoint.
*/
if ((buf_state & mask) == mask && !(buf_state & BM_TEMP))
{
CkptSortItem *item;
buf_state |= BM_CHECKPOINT_NEEDED;
item = &CkptBufferIds[num_to_scan++];
item->buf_id = buf_id;
item->tsId = bufHdr->tag.rnode.spcNode;
item->relNode = bufHdr->tag.rnode.relNode;
item->forkNum = bufHdr->tag.forkNum;
item->blockNum = bufHdr->tag.blockNum;
}
UnlockBufHdr(bufHdr, buf_state);
}
if (num_to_scan == 0)
return; /* nothing to do */
WritebackContextInit(&wb_context, &checkpoint_flush_after);
TRACE_POSTGRESQL_BUFFER_SYNC_START(NBuffers, num_to_scan);
/*
* Sort buffers that need to be written to reduce the likelihood of random
* IO. The sorting is also important for the implementation of balancing
* writes between tablespaces. Without balancing writes we'd potentially
* end up writing to the tablespaces one-by-one; possibly overloading the
* underlying system.
*/
qsort(CkptBufferIds, num_to_scan, sizeof(CkptSortItem),
ckpt_buforder_comparator);
num_spaces = 0;
/*
* Allocate progress status for each tablespace with buffers that need to
* be flushed. This requires the to-be-flushed array to be sorted.
*/
last_tsid = InvalidOid;
for (i = 0; i < num_to_scan; i++)
{
CkptTsStatus *s;
Oid cur_tsid;
cur_tsid = CkptBufferIds[i].tsId;
/*
* Grow array of per-tablespace status structs, every time a new
* tablespace is found.
*/
if (last_tsid == InvalidOid || last_tsid != cur_tsid)
{
Size sz;
num_spaces++;
/*
* Not worth adding grow-by-power-of-2 logic here - even with a
* few hundred tablespaces this should be fine.
*/
sz = sizeof(CkptTsStatus) * num_spaces;
if (per_ts_stat == NULL)
per_ts_stat = (CkptTsStatus *) palloc(sz);
else
per_ts_stat = (CkptTsStatus *) repalloc(per_ts_stat, sz);
s = &per_ts_stat[num_spaces - 1];
memset(s, 0, sizeof(*s));
s->tsId = cur_tsid;
/*
* The first buffer in this tablespace. As CkptBufferIds is sorted
* by tablespace all (s->num_to_scan) buffers in this tablespace
* will follow afterwards.
*/
s->index = i;
/*
* progress_slice will be determined once we know how many buffers
* are in each tablespace, i.e. after this loop.
*/
last_tsid = cur_tsid;
}
else
{
s = &per_ts_stat[num_spaces - 1];
}
s->num_to_scan++;
}
Assert(num_spaces > 0);
/*
* Build a min-heap over the write-progress in the individual tablespaces,
* and compute how large a portion of the total progress a single
* processed buffer is.
*/
ts_heap = binaryheap_allocate(num_spaces,
ts_ckpt_progress_comparator,
NULL);
for (i = 0; i < num_spaces; i++)
{
CkptTsStatus *ts_stat = &per_ts_stat[i];
ts_stat->progress_slice = (float8) num_to_scan / ts_stat->num_to_scan;
binaryheap_add_unordered(ts_heap, PointerGetDatum(ts_stat));
}
binaryheap_build(ts_heap);
/*
* Iterate through to-be-checkpointed buffers and write the ones (still)
* marked with BM_CHECKPOINT_NEEDED. The writes are balanced between
* tablespaces; otherwise the sorting would lead to only one tablespace
* receiving writes at a time, making inefficient use of the hardware.
*/
num_processed = 0;
num_written = 0;
while (!binaryheap_empty(ts_heap))
{
BufferDesc *bufHdr = NULL;
CkptTsStatus *ts_stat = (CkptTsStatus *)
DatumGetPointer(binaryheap_first(ts_heap));
buf_id = CkptBufferIds[ts_stat->index].buf_id;
Assert(buf_id != -1);
bufHdr = GetBufferDescriptor(buf_id);
num_processed++;
/*
* We don't need to acquire the lock here, because we're only looking
* at a single bit. It's possible that someone else writes the buffer
* and clears the flag right after we check, but that doesn't matter
* since SyncOneBuffer will then do nothing. However, there is a
* further race condition: it's conceivable that between the time we
* examine the bit here and the time SyncOneBuffer acquires the lock,
* someone else not only wrote the buffer but replaced it with another
* page and dirtied it. In that improbable case, SyncOneBuffer will
* write the buffer though we didn't need to. It doesn't seem worth
* guarding against this, though.
*/
if (pg_atomic_read_u32(&bufHdr->state) & BM_CHECKPOINT_NEEDED)
{
if (SyncOneBuffer(buf_id, false, &wb_context) & BUF_WRITTEN)
{
TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(buf_id);
BgWriterStats.m_buf_written_checkpoints++;
num_written++;
}
}
/*
* Measure progress independent of actually having to flush the buffer
* - otherwise writing become unbalanced.
*/
ts_stat->progress += ts_stat->progress_slice;
ts_stat->num_scanned++;
ts_stat->index++;
/* Have all the buffers from the tablespace been processed? */
if (ts_stat->num_scanned == ts_stat->num_to_scan)
{
binaryheap_remove_first(ts_heap);
}
else
{
/* update heap with the new progress */
binaryheap_replace_first(ts_heap, PointerGetDatum(ts_stat));
}
/*
* Sleep to throttle our I/O rate.
*/
CheckpointWriteDelay(flags, (double) num_processed / num_to_scan);
}
/* issue all pending flushes */
IssuePendingWritebacks(&wb_context);
pfree(per_ts_stat);
per_ts_stat = NULL;
binaryheap_free(ts_heap);
/*
* Update checkpoint statistics. As noted above, this doesn't include
* buffers written by other backends or bgwriter scan.
*/
CheckpointStats.ckpt_bufs_written += num_written;
TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_scan);
}
/*
* BgBufferSync -- Write out some dirty buffers in the pool.
*
* This is called periodically by the background writer process.
*
* Returns true if it's appropriate for the bgwriter process to go into
* low-power hibernation mode. (This happens if the strategy clock sweep
* has been "lapped" and no buffer allocations have occurred recently,
* or if the bgwriter has been effectively disabled by setting
* bgwriter_lru_maxpages to 0.)
*/
bool
BgBufferSync(WritebackContext *wb_context)
{
/* info obtained from freelist.c */
int strategy_buf_id;
uint32 strategy_passes;
uint32 recent_alloc;
/*
* Information saved between calls so we can determine the strategy
* point's advance rate and avoid scanning already-cleaned buffers.
*/
static bool saved_info_valid = false;
static int prev_strategy_buf_id;
static uint32 prev_strategy_passes;
static int next_to_clean;
static uint32 next_passes;
/* Moving averages of allocation rate and clean-buffer density */
static float smoothed_alloc = 0;
static float smoothed_density = 10.0;
/* Potentially these could be tunables, but for now, not */
float smoothing_samples = 16;
float scan_whole_pool_milliseconds = 120000.0;
/* Used to compute how far we scan ahead */
long strategy_delta;
int bufs_to_lap;
int bufs_ahead;
float scans_per_alloc;
int reusable_buffers_est;
int upcoming_alloc_est;
int min_scan_buffers;
/* Variables for the scanning loop proper */
int num_to_scan;
int num_written;
int reusable_buffers;
bool skip_recently_used;
/* Variables for final smoothed_density update */
long new_strategy_delta;
uint32 new_recent_alloc;
/*
* Find out where the freelist clock sweep currently is, and how many
* buffer allocations have happened since our last call.
*/
strategy_buf_id = StrategySyncStart(&strategy_passes, &recent_alloc);
/* Report buffer alloc counts to pgstat */
BgWriterStats.m_buf_alloc += recent_alloc;
/*
* If we're not running the LRU scan, just stop after doing the stats
* stuff. We mark the saved state invalid so that we can recover sanely
* if LRU scan is turned back on later.
*/
if (bgwriter_lru_maxpages <= 0)
{
saved_info_valid = false;
return true;
}
/*
* Compute strategy_delta = how many buffers have been scanned by the
* clock sweep since last time. If first time through, assume none. Then
* see if we are still ahead of the clock sweep, and if so, how many
* buffers we could scan before we'd catch up with it and "lap" it. Note:
* weird-looking coding of xxx_passes comparisons are to avoid bogus
* behavior when the passes counts wrap around.
*/
if (saved_info_valid)
{
int32 passes_delta = strategy_passes - prev_strategy_passes;
strategy_delta = strategy_buf_id - prev_strategy_buf_id;
strategy_delta += (long) passes_delta * NBuffers;
Assert(strategy_delta >= 0);
if ((int32) (next_passes - strategy_passes) > 0)
{
/* we're one pass ahead of the strategy point */
bufs_to_lap = strategy_buf_id - next_to_clean;
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter ahead: bgw %u-%u strategy %u-%u delta=%ld lap=%d",
next_passes, next_to_clean,
strategy_passes, strategy_buf_id,
strategy_delta, bufs_to_lap);
#endif
}
else if (next_passes == strategy_passes &&
next_to_clean >= strategy_buf_id)
{
/* on same pass, but ahead or at least not behind */
bufs_to_lap = NBuffers - (next_to_clean - strategy_buf_id);
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter ahead: bgw %u-%u strategy %u-%u delta=%ld lap=%d",
next_passes, next_to_clean,
strategy_passes, strategy_buf_id,
strategy_delta, bufs_to_lap);
#endif
}
else
{
/*
* We're behind, so skip forward to the strategy point and start
* cleaning from there.
*/
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter behind: bgw %u-%u strategy %u-%u delta=%ld",
next_passes, next_to_clean,
strategy_passes, strategy_buf_id,
strategy_delta);
#endif
next_to_clean = strategy_buf_id;
next_passes = strategy_passes;
bufs_to_lap = NBuffers;
}
}
else
{
/*
* Initializing at startup or after LRU scanning had been off. Always
* start at the strategy point.
*/
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter initializing: strategy %u-%u",
strategy_passes, strategy_buf_id);
#endif
strategy_delta = 0;
next_to_clean = strategy_buf_id;
next_passes = strategy_passes;
bufs_to_lap = NBuffers;
}
/* Update saved info for next time */
prev_strategy_buf_id = strategy_buf_id;
prev_strategy_passes = strategy_passes;
saved_info_valid = true;
/*
* Compute how many buffers had to be scanned for each new allocation, ie,
* 1/density of reusable buffers, and track a moving average of that.
*
* If the strategy point didn't move, we don't update the density estimate
*/
if (strategy_delta > 0 && recent_alloc > 0)
{
scans_per_alloc = (float) strategy_delta / (float) recent_alloc;
smoothed_density += (scans_per_alloc - smoothed_density) /
smoothing_samples;
}
/*
* Estimate how many reusable buffers there are between the current
* strategy point and where we've scanned ahead to, based on the smoothed
* density estimate.
*/
bufs_ahead = NBuffers - bufs_to_lap;
reusable_buffers_est = (float) bufs_ahead / smoothed_density;
/*
* Track a moving average of recent buffer allocations. Here, rather than
* a true average we want a fast-attack, slow-decline behavior: we
* immediately follow any increase.
*/
if (smoothed_alloc <= (float) recent_alloc)
smoothed_alloc = recent_alloc;
else
smoothed_alloc += ((float) recent_alloc - smoothed_alloc) /
smoothing_samples;
/* Scale the estimate by a GUC to allow more aggressive tuning. */
upcoming_alloc_est = (int) (smoothed_alloc * bgwriter_lru_multiplier);
/*
* If recent_alloc remains at zero for many cycles, smoothed_alloc will
* eventually underflow to zero, and the underflows produce annoying
* kernel warnings on some platforms. Once upcoming_alloc_est has gone to
* zero, there's no point in tracking smaller and smaller values of
* smoothed_alloc, so just reset it to exactly zero to avoid this
* syndrome. It will pop back up as soon as recent_alloc increases.
*/
if (upcoming_alloc_est == 0)
smoothed_alloc = 0;
/*
* Even in cases where there's been little or no buffer allocation
* activity, we want to make a small amount of progress through the buffer
* cache so that as many reusable buffers as possible are clean after an
* idle period.
*
* (scan_whole_pool_milliseconds / BgWriterDelay) computes how many times
* the BGW will be called during the scan_whole_pool time; slice the
* buffer pool into that many sections.
*/
min_scan_buffers = (int) (NBuffers / (scan_whole_pool_milliseconds / BgWriterDelay));
#ifdef FAULT_INJECTOR
/* flush all buffers. */
if (SIMPLE_FAULT_INJECTOR("bg_buffer_sync_default_logic") == FaultInjectorTypeSkip)
min_scan_buffers = NBuffers;
#endif
if (upcoming_alloc_est < (min_scan_buffers + reusable_buffers_est))
{
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter: alloc_est=%d too small, using min=%d + reusable_est=%d",
upcoming_alloc_est, min_scan_buffers, reusable_buffers_est);
#endif
upcoming_alloc_est = min_scan_buffers + reusable_buffers_est;
}
/*
* Now write out dirty reusable buffers, working forward from the
* next_to_clean point, until we have lapped the strategy scan, or cleaned
* enough buffers to match our estimate of the next cycle's allocation
* requirements, or hit the bgwriter_lru_maxpages limit.
*/
/* Make sure we can handle the pin inside SyncOneBuffer */
ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
num_to_scan = bufs_to_lap;
#ifdef FAULT_INJECTOR
/* Flush all buffers. */
if (SIMPLE_FAULT_INJECTOR("bg_buffer_sync_default_logic") == FaultInjectorTypeSkip)
num_to_scan = NBuffers;
#endif
num_written = 0;
reusable_buffers = reusable_buffers_est;
skip_recently_used = true;
#ifdef FAULT_INJECTOR
if (SIMPLE_FAULT_INJECTOR("bg_buffer_sync_default_logic") == FaultInjectorTypeSkip)
skip_recently_used= false;
#endif
/* Execute the LRU scan */
while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est)
{
int sync_state = SyncOneBuffer(next_to_clean, skip_recently_used,
wb_context);
if (++next_to_clean >= NBuffers)
{
next_to_clean = 0;
next_passes++;
}
num_to_scan--;
if (sync_state & BUF_WRITTEN)
{
reusable_buffers++;
if (++num_written >= bgwriter_lru_maxpages)
{
BgWriterStats.m_maxwritten_clean++;
break;
}
}
else if (sync_state & BUF_REUSABLE)
reusable_buffers++;
}
BgWriterStats.m_buf_written_clean += num_written;
#ifdef BGW_DEBUG
elog(DEBUG1, "bgwriter: recent_alloc=%u smoothed=%.2f delta=%ld ahead=%d density=%.2f reusable_est=%d upcoming_est=%d scanned=%d wrote=%d reusable=%d",
recent_alloc, smoothed_alloc, strategy_delta, bufs_ahead,
smoothed_density, reusable_buffers_est, upcoming_alloc_est,
bufs_to_lap - num_to_scan,
num_written,
reusable_buffers - reusable_buffers_est);
#endif
/*
* Consider the above scan as being like a new allocation scan.
* Characterize its density and update the smoothed one based on it. This
* effectively halves the moving average period in cases where both the
* strategy and the background writer are doing some useful scanning,
* which is helpful because a long memory isn't as desirable on the
* density estimates.
*/
new_strategy_delta = bufs_to_lap - num_to_scan;
new_recent_alloc = reusable_buffers - reusable_buffers_est;
if (new_strategy_delta > 0 && new_recent_alloc > 0)
{
scans_per_alloc = (float) new_strategy_delta / (float) new_recent_alloc;
smoothed_density += (scans_per_alloc - smoothed_density) /
smoothing_samples;
#ifdef BGW_DEBUG
elog(DEBUG2, "bgwriter: cleaner density alloc=%u scan=%ld density=%.2f new smoothed=%.2f",
new_recent_alloc, new_strategy_delta,
scans_per_alloc, smoothed_density);
#endif
}
/* Return true if OK to hibernate */
return (bufs_to_lap == 0 && recent_alloc == 0);
}
/*
* SyncOneBuffer -- process a single buffer during syncing.
*
* If skip_recently_used is true, we don't write currently-pinned buffers, nor
* buffers marked recently used, as these are not replacement candidates.
*
* Returns a bitmask containing the following flag bits:
* BUF_WRITTEN: we wrote the buffer.
* BUF_REUSABLE: buffer is available for replacement, ie, it has
* pin count 0 and usage count 0.
*
* (BUF_WRITTEN could be set in error if FlushBuffers finds the buffer clean
* after locking it, but we don't care all that much.)
*
* Note: caller must have done ResourceOwnerEnlargeBuffers.
*/
static int
SyncOneBuffer(int buf_id, bool skip_recently_used, WritebackContext *wb_context)
{
BufferDesc *bufHdr = GetBufferDescriptor(buf_id);
int result = 0;
uint32 buf_state;
BufferTag tag;
ReservePrivateRefCountEntry();
/*
* Check whether buffer needs writing.
*
* We can make this check without taking the buffer content lock so long
* as we mark pages dirty in access methods *before* logging changes with
* XLogInsert(): if someone marks the buffer dirty just after our check we
* don't worry because our checkpoint.redo points before log record for
* upcoming changes and so we are not required to write such dirty buffer.
*/
buf_state = LockBufHdr(bufHdr);
if (BUF_STATE_GET_REFCOUNT(buf_state) == 0 &&
BUF_STATE_GET_USAGECOUNT(buf_state) == 0)
{
result |= BUF_REUSABLE;
}
else if (skip_recently_used)
{
/* Caller told us not to write recently-used buffers */
UnlockBufHdr(bufHdr, buf_state);
return result;
}
if (!(buf_state & BM_VALID) || !(buf_state & BM_DIRTY))
{
/* It's clean, so nothing to do */
UnlockBufHdr(bufHdr, buf_state);
return result;
}
/*
* Pin it, share-lock it, write it. (FlushBuffer will do nothing if the
* buffer is clean by the time we've locked it.)
*/
PinBuffer_Locked(bufHdr);
AcquireContentLock(bufHdr, LW_SHARED);
FlushBuffer(bufHdr, NULL);
ReleaseContentLock(bufHdr);
tag = bufHdr->tag;
UnpinBuffer(bufHdr, true);
ScheduleBufferTagForWriteback(wb_context, &tag);
return result | BUF_WRITTEN;
}
/*
* AtEOXact_Buffers - clean up at end of transaction.
*
* As of PostgreSQL 8.0, buffer pins should get released by the
* ResourceOwner mechanism. This routine is just a debugging
* cross-check that no pins remain.
*/
void
AtEOXact_Buffers(bool isCommit)
{
CheckForBufferLeaks();
AtEOXact_LocalBuffers(isCommit);
Assert(PrivateRefCountOverflowed == 0);
}
/*
* Initialize access to shared buffer pool
*
* This is called during backend startup (whether standalone or under the
* postmaster). It sets up for this backend's access to the already-existing
* buffer pool.
*
* NB: this is called before InitProcess(), so we do not have a PGPROC and
* cannot do LWLockAcquire; hence we can't actually access stuff in
* shared memory yet. We are only initializing local data here.
* (See also InitBufferPoolBackend)
*/
void
InitBufferPoolAccess(void)
{
HASHCTL hash_ctl;
memset(&PrivateRefCountArray, 0, sizeof(PrivateRefCountArray));
MemSet(&hash_ctl, 0, sizeof(hash_ctl));
hash_ctl.keysize = sizeof(int32);
hash_ctl.entrysize = sizeof(PrivateRefCountEntry);
PrivateRefCountHash = hash_create("PrivateRefCount", 100, &hash_ctl,
HASH_ELEM | HASH_BLOBS);
}
/*
* InitBufferPoolBackend --- second-stage initialization of a new backend
*
* This is called after we have acquired a PGPROC and so can safely get
* LWLocks. We don't currently need to do anything at this stage ...
* except register a shmem-exit callback. AtProcExit_Buffers needs LWLock
* access, and thereby has to be called at the corresponding phase of
* backend shutdown.
*/
void
InitBufferPoolBackend(void)
{
on_shmem_exit(AtProcExit_Buffers, 0);
}
/*
* During backend exit, ensure that we released all shared-buffer locks and
* assert that we have no remaining pins.
*/
static void
AtProcExit_Buffers(int code, Datum arg)
{
AbortBufferIO();
UnlockBuffers();
CheckForBufferLeaks();
/* localbuf.c needs a chance too */
AtProcExit_LocalBuffers();
}
/*
* CheckForBufferLeaks - ensure this backend holds no buffer pins
*
* As of PostgreSQL 8.0, buffer pins should get released by the
* ResourceOwner mechanism. This routine is just a debugging
* cross-check that no pins remain.
*/
static void
CheckForBufferLeaks(void)
{
#ifdef USE_ASSERT_CHECKING
int RefCountErrors = 0;
PrivateRefCountEntry *res;
int i;
/* check the array */
for (i = 0; i < REFCOUNT_ARRAY_ENTRIES; i++)
{
res = &PrivateRefCountArray[i];
if (res->buffer != InvalidBuffer)
{
PrintBufferLeakWarning(res->buffer);
RefCountErrors++;
}
}
/* if necessary search the hash */
if (PrivateRefCountOverflowed)
{
HASH_SEQ_STATUS hstat;
hash_seq_init(&hstat, PrivateRefCountHash);
while ((res = (PrivateRefCountEntry *) hash_seq_search(&hstat)) != NULL)
{
PrintBufferLeakWarning(res->buffer);
RefCountErrors++;
}
}
Assert(RefCountErrors == 0);
#endif
}
/*
* Helper routine to issue warnings when a buffer is unexpectedly pinned
*/
void
PrintBufferLeakWarning(Buffer buffer)
{
BufferDesc *buf;
int32 loccount;
char *path;
BackendId backend;
uint32 buf_state;
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
{
buf = GetLocalBufferDescriptor(-buffer - 1);
loccount = LocalRefCount[-buffer - 1];
backend = MyBackendId;
}
else
{
buf = GetBufferDescriptor(buffer - 1);
loccount = GetPrivateRefCount(buffer);
backend = InvalidBackendId;
}
/* theoretically we should lock the bufhdr here */
path = relpathbackend(buf->tag.rnode, backend, buf->tag.forkNum);
buf_state = pg_atomic_read_u32(&buf->state);
elog(WARNING,
"buffer refcount leak: [%03d] "
"(rel=%s, blockNum=%u, flags=0x%x, refcount=%u %d)",
buffer, path,
buf->tag.blockNum, buf_state & BUF_FLAG_MASK,
BUF_STATE_GET_REFCOUNT(buf_state), loccount);
pfree(path);
}
/*
* CheckPointBuffers
*
* Flush all dirty blocks in buffer pool to disk at checkpoint time.
*
* Note: temporary relations do not participate in checkpoints, so they don't
* need to be flushed.
*/
void
CheckPointBuffers(int flags)
{
TRACE_POSTGRESQL_BUFFER_CHECKPOINT_START(flags);
CheckpointStats.ckpt_write_t = GetCurrentTimestamp();
BufferSync(flags);
CheckpointStats.ckpt_sync_t = GetCurrentTimestamp();
TRACE_POSTGRESQL_BUFFER_CHECKPOINT_SYNC_START();
ProcessSyncRequests();
CheckpointStats.ckpt_sync_end_t = GetCurrentTimestamp();
TRACE_POSTGRESQL_BUFFER_CHECKPOINT_DONE();
}
/*
* Do whatever is needed to prepare for commit at the bufmgr and smgr levels
*/
void
BufmgrCommit(void)
{
/* Nothing to do in bufmgr anymore... */
}
/*
* BufferGetBlockNumber
* Returns the block number associated with a buffer.
*
* Note:
* Assumes that the buffer is valid and pinned, else the
* value may be obsolete immediately...
*/
BlockNumber
BufferGetBlockNumber(Buffer buffer)
{
BufferDesc *bufHdr;
Assert(BufferIsPinned(buffer));
if (BufferIsLocal(buffer))
bufHdr = GetLocalBufferDescriptor(-buffer - 1);
else
bufHdr = GetBufferDescriptor(buffer - 1);
/* pinned, so OK to read tag without spinlock */
return bufHdr->tag.blockNum;
}
/*
* BufferGetTag
* Returns the relfilenode, fork number and block number associated with
* a buffer.
*/
void
BufferGetTag(Buffer buffer, RelFileNode *rnode, ForkNumber *forknum,
BlockNumber *blknum)
{
BufferDesc *bufHdr;
/* Do the same checks as BufferGetBlockNumber. */
Assert(BufferIsPinned(buffer));
if (BufferIsLocal(buffer))
bufHdr = GetLocalBufferDescriptor(-buffer - 1);
else
bufHdr = GetBufferDescriptor(buffer - 1);
/* pinned, so OK to read tag without spinlock */
*rnode = bufHdr->tag.rnode;
*forknum = bufHdr->tag.forkNum;
*blknum = bufHdr->tag.blockNum;
}
/*
* FlushBuffer
* Physically write out a shared buffer.
*
* NOTE: this actually just passes the buffer contents to the kernel; the
* real write to disk won't happen until the kernel feels like it. This
* is okay from our point of view since we can redo the changes from WAL.
* However, we will need to force the changes to disk via fsync before
* we can checkpoint WAL.
*
* The caller must hold a pin on the buffer and have share-locked the
* buffer contents. (Note: a share-lock does not prevent updates of
* hint bits in the buffer, so the page could change while the write
* is in progress, but we assume that that will not invalidate the data
* written.)
*
* If the caller has an smgr reference for the buffer's relation, pass it
* as the second parameter. If not, pass NULL.
*/
static void
FlushBuffer(BufferDesc *buf, SMgrRelation reln)
{
XLogRecPtr recptr;
ErrorContextCallback errcallback;
instr_time io_start,
io_time;
Block bufBlock;
char *bufToWrite;
uint32 buf_state;
/*
* Acquire the buffer's io_in_progress lock. If StartBufferIO returns
* false, then someone else flushed the buffer before we could, so we need
* not do anything.
*/
if (!StartBufferIO(buf, false))
return;
/* Setup error traceback support for ereport() */
errcallback.callback = shared_buffer_write_error_callback;
errcallback.arg = (void *) buf;
errcallback.previous = error_context_stack;
error_context_stack = &errcallback;
/* Find smgr relation for buffer */
if (reln == NULL)
{
/* it's OK to check this flag without the buffer header lock,
* it cannot change while we hold a pin on it
*/
uint32 buf_state_unlocked = pg_atomic_read_u32(&buf->state);
bool istemp = (buf_state_unlocked & BM_TEMP) != 0;
reln = smgropen(buf->tag.rnode,
istemp ? TempRelBackendId : InvalidBackendId, 0);
}
TRACE_POSTGRESQL_BUFFER_FLUSH_START(buf->tag.forkNum,
buf->tag.blockNum,
reln->smgr_rnode.node.spcNode,
reln->smgr_rnode.node.dbNode,
reln->smgr_rnode.node.relNode);
buf_state = LockBufHdr(buf);
/*
* Run PageGetLSN while holding header lock, since we don't have the
* buffer locked exclusively in all cases.
*/
recptr = BufferGetLSN(buf);
/* To check if block content changes while flushing. - vadim 01/17/97 */
buf_state &= ~BM_JUST_DIRTIED;
UnlockBufHdr(buf, buf_state);
/*
* Force XLOG flush up to buffer's LSN. This implements the basic WAL
* rule that log updates must hit disk before any of the data-file changes
* they describe do.
*
* However, this rule does not apply to unlogged relations, which will be
* lost after a crash anyway. Most unlogged relation pages do not bear
* LSNs since we never emit WAL records for them, and therefore flushing
* up through the buffer LSN would be useless, but harmless. However,
* GiST indexes use LSNs internally to track page-splits, and therefore
* unlogged GiST pages bear "fake" LSNs generated by
* GetFakeLSNForUnloggedRel. It is unlikely but possible that the fake
* LSN counter could advance past the WAL insertion point; and if it did
* happen, attempting to flush WAL through that location would fail, with
* disastrous system-wide consequences. To make sure that can't happen,
* skip the flush if the buffer isn't permanent.
*/
if (buf_state & BM_PERMANENT)
XLogFlush(recptr);
/*
* Now it's safe to write buffer to disk. Note that no one else should
* have been able to write it while we were busy with log flushing because
* we have the io_in_progress lock.
*/
bufBlock = BufHdrGetBlock(buf);
/*
* Update page checksum if desired. Since we have only shared lock on the
* buffer, other processes might be updating hint bits in it, so we must
* copy the page to private storage if we do checksumming.
*/
bufToWrite = PageSetChecksumCopy((Page) bufBlock, buf->tag.blockNum);
/*
* bufToWrite is either the shared buffer or a copy, as appropriate.
*/
if (track_io_timing)
INSTR_TIME_SET_CURRENT(io_start);
/*
* bufToWrite is either the shared buffer or a copy, as appropriate.
*/
smgrwrite(reln,
buf->tag.forkNum,
buf->tag.blockNum,
bufToWrite,
false);
if (track_io_timing)
{
INSTR_TIME_SET_CURRENT(io_time);
INSTR_TIME_SUBTRACT(io_time, io_start);
pgstat_count_buffer_write_time(INSTR_TIME_GET_MICROSEC(io_time));
INSTR_TIME_ADD(pgBufferUsage.blk_write_time, io_time);
}
pgBufferUsage.shared_blks_written++;
/*
* Mark the buffer as clean (unless BM_JUST_DIRTIED has become set) and
* end the io_in_progress state.
*/
TerminateBufferIO(buf, true, 0);
TRACE_POSTGRESQL_BUFFER_FLUSH_DONE(buf->tag.forkNum,
buf->tag.blockNum,
reln->smgr_rnode.node.spcNode,
reln->smgr_rnode.node.dbNode,
reln->smgr_rnode.node.relNode);
/* Pop the error context stack */
error_context_stack = errcallback.previous;
}
/*
* RelationGetNumberOfBlocksInFork
* Determines the current number of pages in the specified relation fork.
*
* Note that the accuracy of the result will depend on the details of the
* relation's storage. For builtin AMs it'll be accurate, but for external AMs
* it might not be.
*/
BlockNumber
RelationGetNumberOfBlocksInFork(Relation relation, ForkNumber forkNum)
{
switch (relation->rd_rel->relkind)
{
case RELKIND_SEQUENCE:
case RELKIND_INDEX:
case RELKIND_PARTITIONED_INDEX:
/* Open it at the smgr level if not already done */
RelationOpenSmgr(relation);
return smgrnblocks(relation->rd_smgr, forkNum);
case RELKIND_RELATION:
case RELKIND_TOASTVALUE:
case RELKIND_MATVIEW:
case RELKIND_AOSEGMENTS:
case RELKIND_AOVISIMAP:
case RELKIND_AOBLOCKDIR:
{
/*
* Not every table AM uses BLCKSZ wide fixed size blocks.
* Therefore tableam returns the size in bytes - but for the
* purpose of this routine, we want the number of blocks.
* Therefore divide, rounding up.
*/
uint64 szbytes;
szbytes = table_relation_size(relation, forkNum);
return (szbytes + (BLCKSZ - 1)) / BLCKSZ;
}
case RELKIND_VIEW:
case RELKIND_COMPOSITE_TYPE:
case RELKIND_FOREIGN_TABLE:
case RELKIND_PARTITIONED_TABLE:
default:
Assert(false);
break;
}
return 0; /* keep compiler quiet */
}
/*
* GPDB: it is possible to need to calculate the number of blocks from the table
* size. An example use case is when we are the dispatcher and we need to
* acquire the number of blocks from all segments.
*
* Use the same calculation that RelationGetNumberOfBlocksInFork is using.
*/
BlockNumber
RelationGuessNumberOfBlocksFromSize(uint64 szbytes)
{
return (szbytes + (BLCKSZ - 1)) / BLCKSZ;
}
/*
* BufferIsPermanent
* Determines whether a buffer will potentially still be around after
* a crash. Caller must hold a buffer pin.
*/
bool
BufferIsPermanent(Buffer buffer)
{
BufferDesc *bufHdr;
/* Local buffers are used only for temp relations. */
if (BufferIsLocal(buffer))
return false;
/* Make sure we've got a real buffer, and that we hold a pin on it. */
Assert(BufferIsValid(buffer));
Assert(BufferIsPinned(buffer));
/*
* BM_PERMANENT can't be changed while we hold a pin on the buffer, so we
* need not bother with the buffer header spinlock. Even if someone else
* changes the buffer header state while we're doing this, the state is
* changed atomically, so we'll read the old value or the new value, but
* not random garbage.
*/
bufHdr = GetBufferDescriptor(buffer - 1);
return (pg_atomic_read_u32(&bufHdr->state) & BM_PERMANENT) != 0;
}
/*
* BufferGetLSNAtomic
* Retrieves the LSN of the buffer atomically using a buffer header lock.
* This is necessary for some callers who may not have an exclusive lock
* on the buffer.
*/
XLogRecPtr
BufferGetLSNAtomic(Buffer buffer)
{
BufferDesc *bufHdr = GetBufferDescriptor(buffer - 1);
char *page = BufferGetPage(buffer);
XLogRecPtr lsn;
uint32 buf_state;
/*
* If we don't need locking for correctness, fastpath out.
*/
if (!XLogHintBitIsNeeded() || BufferIsLocal(buffer))
return PageGetLSN(page);
/* Make sure we've got a real buffer, and that we hold a pin on it. */
Assert(BufferIsValid(buffer));
Assert(BufferIsPinned(buffer));
buf_state = LockBufHdr(bufHdr);
lsn = PageGetLSN(page);
UnlockBufHdr(bufHdr, buf_state);
return lsn;
}
/* ---------------------------------------------------------------------
* DropRelFileNodeBuffers
*
* This function removes from the buffer pool all the pages of the
* specified relation fork that have block numbers >= firstDelBlock.
* (In particular, with firstDelBlock = 0, all pages are removed.)
* Dirty pages are simply dropped, without bothering to write them
* out first. Therefore, this is NOT rollback-able, and so should be
* used only with extreme caution!
*
* Currently, this is called only from smgr.c when the underlying file
* is about to be deleted or truncated (firstDelBlock is needed for
* the truncation case). The data in the affected pages would therefore
* be deleted momentarily anyway, and there is no point in writing it.
* It is the responsibility of higher-level code to ensure that the
* deletion or truncation does not lose any data that could be needed
* later. It is also the responsibility of higher-level code to ensure
* that no other process could be trying to load more pages of the
* relation into buffers.
*
* XXX currently it sequentially searches the buffer pool, should be
* changed to more clever ways of searching. However, this routine
* is used only in code paths that aren't very performance-critical,
* and we shouldn't slow down the hot paths to make it faster ...
* --------------------------------------------------------------------
*/
void
DropRelFileNodeBuffers(RelFileNodeBackend rnode, ForkNumber forkNum,
BlockNumber firstDelBlock)
{
int i;
/* Temp tables use shared buffers in Greenplum */
/* If it's a local relation, it's localbuf.c's problem. */
#if 0
if (RelFileNodeBackendIsTemp(rnode))
{
if (rnode.backend == MyBackendId)
DropRelFileNodeLocalBuffers(rnode.node, forkNum, firstDelBlock);
return;
}
#endif
for (i = 0; i < NBuffers; i++)
{
BufferDesc *bufHdr = GetBufferDescriptor(i);
uint32 buf_state;
/*
* We can make this a tad faster by prechecking the buffer tag before
* we attempt to lock the buffer; this saves a lot of lock
* acquisitions in typical cases. It should be safe because the
* caller must have AccessExclusiveLock on the relation, or some other
* reason to be certain that no one is loading new pages of the rel
* into the buffer pool. (Otherwise we might well miss such pages
* entirely.) Therefore, while the tag might be changing while we
* look at it, it can't be changing *to* a value we care about, only
* *away* from such a value. So false negatives are impossible, and
* false positives are safe because we'll recheck after getting the
* buffer lock.
*
* We could check forkNum and blockNum as well as the rnode, but the
* incremental win from doing so seems small.
*/
if (!RelFileNodeEquals(bufHdr->tag.rnode, rnode.node))
continue;
buf_state = LockBufHdr(bufHdr);
if (RelFileNodeEquals(bufHdr->tag.rnode, rnode.node) &&
bufHdr->tag.forkNum == forkNum &&
bufHdr->tag.blockNum >= firstDelBlock)
InvalidateBuffer(bufHdr); /* releases spinlock */
else
UnlockBufHdr(bufHdr, buf_state);
}
}
/* ---------------------------------------------------------------------
* DropRelFileNodesAllBuffers
*
* This function removes from the buffer pool all the pages of all
* forks of the specified relations. It's equivalent to calling
* DropRelFileNodeBuffers once per fork per relation with
* firstDelBlock = 0.
* --------------------------------------------------------------------
*/
void
DropRelFileNodesAllBuffers(RelFileNodeBackend *rnodes, int nnodes)
{
int i,
n = 0;
RelFileNode *nodes;
bool use_bsearch;
if (nnodes == 0)
return;
nodes = palloc(sizeof(RelFileNode) * nnodes); /* non-local relations */
/* Temp tables use shared buffers in Greenplum */
/* If it's a local relation, it's localbuf.c's problem. */
for (i = 0; i < nnodes; i++)
{
#if 0
if (RelFileNodeBackendIsTemp(rnodes[i]))
{
if (rnodes[i].backend == MyBackendId)
DropRelFileNodeAllLocalBuffers(rnodes[i].node);
}
else
#endif
nodes[n++] = rnodes[i].node;
}
/*
* If there are no non-local relations, then we're done. Release the
* memory and return.
*/
if (n == 0)
{
pfree(nodes);
return;
}
/*
* For low number of relations to drop just use a simple walk through, to
* save the bsearch overhead. The threshold to use is rather a guess than
* an exactly determined value, as it depends on many factors (CPU and RAM
* speeds, amount of shared buffers etc.).
*/
use_bsearch = n > DROP_RELS_BSEARCH_THRESHOLD;
/* sort the list of rnodes if necessary */
if (use_bsearch)
pg_qsort(nodes, n, sizeof(RelFileNode), rnode_comparator);
for (i = 0; i < NBuffers; i++)
{
RelFileNode *rnode = NULL;
BufferDesc *bufHdr = GetBufferDescriptor(i);
uint32 buf_state;
/*
* As in DropRelFileNodeBuffers, an unlocked precheck should be safe
* and saves some cycles.
*/
if (!use_bsearch)
{
int j;
for (j = 0; j < n; j++)
{
if (RelFileNodeEquals(bufHdr->tag.rnode, nodes[j]))
{
rnode = &nodes[j];
break;
}
}
}
else
{
rnode = bsearch((const void *) &(bufHdr->tag.rnode),
nodes, n, sizeof(RelFileNode),
rnode_comparator);
}
/* buffer doesn't belong to any of the given relfilenodes; skip it */
if (rnode == NULL)
continue;
buf_state = LockBufHdr(bufHdr);
if (RelFileNodeEquals(bufHdr->tag.rnode, (*rnode)))
InvalidateBuffer(bufHdr); /* releases spinlock */
else
UnlockBufHdr(bufHdr, buf_state);
}
pfree(nodes);
}
/* ---------------------------------------------------------------------
* DropDatabaseBuffers
*
* This function removes all the buffers in the buffer cache for a
* particular database. Dirty pages are simply dropped, without
* bothering to write them out first. This is used when we destroy a
* database, to avoid trying to flush data to disk when the directory
* tree no longer exists. Implementation is pretty similar to
* DropRelFileNodeBuffers() which is for destroying just one relation.
* --------------------------------------------------------------------
*/
void
DropDatabaseBuffers(Oid dbid)
{
int i;
/*
* We needn't consider local buffers, since by assumption the target
* database isn't our own.
*/
for (i = 0; i < NBuffers; i++)
{
BufferDesc *bufHdr = GetBufferDescriptor(i);
uint32 buf_state;
/*
* As in DropRelFileNodeBuffers, an unlocked precheck should be safe
* and saves some cycles.
*/
if (bufHdr->tag.rnode.dbNode != dbid)
continue;
buf_state = LockBufHdr(bufHdr);
if (bufHdr->tag.rnode.dbNode == dbid)
InvalidateBuffer(bufHdr); /* releases spinlock */
else
UnlockBufHdr(bufHdr, buf_state);
}
}
/* -----------------------------------------------------------------
* PrintBufferDescs
*
* this function prints all the buffer descriptors, for debugging
* use only.
* -----------------------------------------------------------------
*/
#ifdef NOT_USED
void
PrintBufferDescs(void)
{
int i;
for (i = 0; i < NBuffers; ++i)
{
BufferDesc *buf = GetBufferDescriptor(i);
Buffer b = BufferDescriptorGetBuffer(buf);
/* theoretically we should lock the bufhdr here */
elog(LOG,
"[%02d] (freeNext=%d, rel=%s, "
"blockNum=%u, flags=0x%x, refcount=%u %d)",
i, buf->freeNext,
relpathbackend(buf->tag.rnode, InvalidBackendId, buf->tag.forkNum),
buf->tag.blockNum, buf->flags,
buf->refcount, GetPrivateRefCount(b));
}
}
#endif
#ifdef NOT_USED
void
PrintPinnedBufs(void)
{
int i;
for (i = 0; i < NBuffers; ++i)
{
BufferDesc *buf = GetBufferDescriptor(i);
Buffer b = BufferDescriptorGetBuffer(buf);
if (GetPrivateRefCount(b) > 0)
{
/* theoretically we should lock the bufhdr here */
elog(LOG,
"[%02d] (freeNext=%d, rel=%s, "
"blockNum=%u, flags=0x%x, refcount=%u %d)",
i, buf->freeNext,
relpathperm(buf->tag.rnode, buf->tag.forkNum),
buf->tag.blockNum, buf->flags,
buf->refcount, GetPrivateRefCount(b));
}
}
}
#endif
/* ---------------------------------------------------------------------
* FlushRelationBuffers
*
* This function writes all dirty pages of a relation out to disk
* (or more accurately, out to kernel disk buffers), ensuring that the
* kernel has an up-to-date view of the relation.
*
* Generally, the caller should be holding AccessExclusiveLock on the
* target relation to ensure that no other backend is busy dirtying
* more blocks of the relation; the effects can't be expected to last
* after the lock is released.
*
* XXX currently it sequentially searches the buffer pool, should be
* changed to more clever ways of searching. This routine is not
* used in any performance-critical code paths, so it's not worth
* adding additional overhead to normal paths to make it go faster;
* but see also DropRelFileNodeBuffers.
* --------------------------------------------------------------------
*/
void
FlushRelationBuffers(Relation rel)
{
int i;
BufferDesc *bufHdr;
/* Open rel at the smgr level if not already done */
RelationOpenSmgr(rel);
if (!RelationUsesBufferManager(rel))
return;
if (RelationUsesLocalBuffers(rel))
{
for (i = 0; i < NLocBuffer; i++)
{
uint32 buf_state;
bufHdr = GetLocalBufferDescriptor(i);
if (RelFileNodeEquals(bufHdr->tag.rnode, rel->rd_node) &&
((buf_state = pg_atomic_read_u32(&bufHdr->state)) &
(BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
{
ErrorContextCallback errcallback;
Page localpage;
localpage = (char *) LocalBufHdrGetBlock(bufHdr);
/* Setup error traceback support for ereport() */
errcallback.callback = local_buffer_write_error_callback;
errcallback.arg = (void *) bufHdr;
errcallback.previous = error_context_stack;
error_context_stack = &errcallback;
PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
smgrwrite(rel->rd_smgr,
bufHdr->tag.forkNum,
bufHdr->tag.blockNum,
localpage,
false);
buf_state &= ~(BM_DIRTY | BM_JUST_DIRTIED);
pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
/* Pop the error context stack */
error_context_stack = errcallback.previous;
}
}
return;
}
/* Make sure we can handle the pin inside the loop */
ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
for (i = 0; i < NBuffers; i++)
{
uint32 buf_state;
bufHdr = GetBufferDescriptor(i);
/*
* As in DropRelFileNodeBuffers, an unlocked precheck should be safe
* and saves some cycles.
*/
if (!RelFileNodeEquals(bufHdr->tag.rnode, rel->rd_node))
continue;
ReservePrivateRefCountEntry();
buf_state = LockBufHdr(bufHdr);
if (RelFileNodeEquals(bufHdr->tag.rnode, rel->rd_node) &&
(buf_state & (BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
{
PinBuffer_Locked(bufHdr);
AcquireContentLock(bufHdr, LW_SHARED);
FlushBuffer(bufHdr, rel->rd_smgr);
ReleaseContentLock(bufHdr);
UnpinBuffer(bufHdr, true);
}
else
UnlockBufHdr(bufHdr, buf_state);
}
}
/* ---------------------------------------------------------------------
* FlushDatabaseBuffers
*
* This function writes all dirty pages of a database out to disk
* (or more accurately, out to kernel disk buffers), ensuring that the
* kernel has an up-to-date view of the database.
*
* Generally, the caller should be holding an appropriate lock to ensure
* no other backend is active in the target database; otherwise more
* pages could get dirtied.
*
* Note we don't worry about flushing any pages of temporary relations.
* It's assumed these wouldn't be interesting.
* --------------------------------------------------------------------
*/
void
FlushDatabaseBuffers(Oid dbid)
{
int i;
BufferDesc *bufHdr;
/* Make sure we can handle the pin inside the loop */
ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
for (i = 0; i < NBuffers; i++)
{
uint32 buf_state;
bufHdr = GetBufferDescriptor(i);
/*
* As in DropRelFileNodeBuffers, an unlocked precheck should be safe
* and saves some cycles.
*/
if (bufHdr->tag.rnode.dbNode != dbid)
continue;
ReservePrivateRefCountEntry();
buf_state = LockBufHdr(bufHdr);
if (bufHdr->tag.rnode.dbNode == dbid &&
(buf_state & (BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
{
PinBuffer_Locked(bufHdr);
AcquireContentLock(bufHdr, LW_SHARED);
FlushBuffer(bufHdr, NULL);
ReleaseContentLock(bufHdr);
UnpinBuffer(bufHdr, true);
}
else
UnlockBufHdr(bufHdr, buf_state);
}
}
/*
* Flush a previously, shared or exclusively, locked and pinned buffer to the
* OS.
*/
void
FlushOneBuffer(Buffer buffer)
{
BufferDesc *bufHdr;
/* currently not needed, but no fundamental reason not to support */
Assert(!BufferIsLocal(buffer));
Assert(BufferIsPinned(buffer));
bufHdr = GetBufferDescriptor(buffer - 1);
Assert(LWLockHeldByMe(BufferDescriptorGetContentLock(bufHdr)));
FlushBuffer(bufHdr, NULL);
}
/*
* ReleaseBuffer -- release the pin on a buffer
*/
void
ReleaseBuffer(Buffer buffer)
{
if (!BufferIsValid(buffer))
elog(ERROR, "bad buffer ID: %d", buffer);
if (BufferIsLocal(buffer))
{
ResourceOwnerForgetBuffer(CurrentResourceOwner, buffer);
Assert(LocalRefCount[-buffer - 1] > 0);
LocalRefCount[-buffer - 1]--;
return;
}
UnpinBuffer(GetBufferDescriptor(buffer - 1), true);
}
/*
* UnlockReleaseBuffer -- release the content lock and pin on a buffer
*
* This is just a shorthand for a common combination.
*/
void
UnlockReleaseBuffer(Buffer buffer)
{
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
ReleaseBuffer(buffer);
}
/*
* IncrBufferRefCount
* Increment the pin count on a buffer that we have *already* pinned
* at least once.
*
* This function cannot be used on a buffer we do not have pinned,
* because it doesn't change the shared buffer state.
*/
void
IncrBufferRefCount(Buffer buffer)
{
Assert(BufferIsPinned(buffer));
ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
if (BufferIsLocal(buffer))
LocalRefCount[-buffer - 1]++;
else
{
PrivateRefCountEntry *ref;
ref = GetPrivateRefCountEntry(buffer, true);
Assert(ref != NULL);
ref->refcount++;
}
ResourceOwnerRememberBuffer(CurrentResourceOwner, buffer);
}
/*
* MarkBufferDirtyHint
*
* Mark a buffer dirty for non-critical changes.
*
* This is essentially the same as MarkBufferDirty, except:
*
* 1. The caller does not write WAL; so if checksums are enabled, we may need
* to write an XLOG_FPI WAL record to protect against torn pages.
* 2. The caller might have only share-lock instead of exclusive-lock on the
* buffer's content lock.
* 3. This function does not guarantee that the buffer is always marked dirty
* (due to a race condition), so it cannot be used for important changes.
*/
void
MarkBufferDirtyHint(Buffer buffer, bool buffer_std)
{
BufferDesc *bufHdr;
Page page = BufferGetPage(buffer);
if (!BufferIsValid(buffer))
elog(ERROR, "bad buffer ID: %d", buffer);
if (BufferIsLocal(buffer))
{
MarkLocalBufferDirty(buffer);
return;
}
bufHdr = GetBufferDescriptor(buffer - 1);
Assert(GetPrivateRefCount(buffer) > 0);
/* here, either share or exclusive lock is OK */
Assert(LWLockHeldByMe(BufferDescriptorGetContentLock(bufHdr)));
/*
* This routine might get called many times on the same page, if we are
* making the first scan after commit of an xact that added/deleted many
* tuples. So, be as quick as we can if the buffer is already dirty. We
* do this by not acquiring spinlock if it looks like the status bits are
* already set. Since we make this test unlocked, there's a chance we
* might fail to notice that the flags have just been cleared, and failed
* to reset them, due to memory-ordering issues. But since this function
* is only intended to be used in cases where failing to write out the
* data would be harmless anyway, it doesn't really matter.
*/
if ((pg_atomic_read_u32(&bufHdr->state) & (BM_DIRTY | BM_JUST_DIRTIED)) !=
(BM_DIRTY | BM_JUST_DIRTIED))
{
XLogRecPtr lsn = InvalidXLogRecPtr;
bool dirtied = false;
bool delayChkpt = false;
uint32 buf_state;
/*
* If we need to protect hint bit updates from torn writes, WAL-log a
* full page image of the page. This full page image is only necessary
* if the hint bit update is the first change to the page since the
* last checkpoint.
*
* We don't check full_page_writes here because that logic is included
* when we call XLogInsert() since the value changes dynamically.
*/
if (XLogHintBitIsNeeded() &&
(pg_atomic_read_u32(&bufHdr->state) & BM_PERMANENT))
{
/*
* If we're in recovery we cannot dirty a page because of a hint.
* We can set the hint, just not dirty the page as a result so the
* hint is lost when we evict the page or shutdown.
*
* See src/backend/storage/page/README for longer discussion.
*/
if (RecoveryInProgress() || IsInitProcessingMode())
return;
/*
* If the block is already dirty because we either made a change
* or set a hint already, then we don't need to write a full page
* image. Note that aggressive cleaning of blocks dirtied by hint
* bit setting would increase the call rate. Bulk setting of hint
* bits would reduce the call rate...
*
* We must issue the WAL record before we mark the buffer dirty.
* Otherwise we might write the page before we write the WAL. That
* causes a race condition, since a checkpoint might occur between
* writing the WAL record and marking the buffer dirty. We solve
* that with a kluge, but one that is already in use during
* transaction commit to prevent race conditions. Basically, we
* simply prevent the checkpoint WAL record from being written
* until we have marked the buffer dirty. We don't start the
* checkpoint flush until we have marked dirty, so our checkpoint
* must flush the change to disk successfully or the checkpoint
* never gets written, so crash recovery will fix.
*
* It's possible we may enter here without an xid, so it is
* essential that CreateCheckpoint waits for virtual transactions
* rather than full transactionids.
*/
MyPgXact->delayChkpt = delayChkpt = true;
lsn = XLogSaveBufferForHint(buffer, buffer_std);
}
buf_state = LockBufHdr(bufHdr);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
if (!(buf_state & BM_DIRTY))
{
dirtied = true; /* Means "will be dirtied by this action" */
/*
* Set the page LSN if we wrote a backup block. We aren't supposed
* to set this when only holding a share lock but as long as we
* serialise it somehow we're OK. We choose to set LSN while
* holding the buffer header lock, which causes any reader of an
* LSN who holds only a share lock to also obtain a buffer header
* lock before using PageGetLSN(), which is enforced in
* BufferGetLSNAtomic().
*
* If checksums are enabled, you might think we should reset the
* checksum here. That will happen when the page is written
* sometime later in this checkpoint cycle.
*/
if (!XLogRecPtrIsInvalid(lsn))
PageSetLSN(page, lsn);
}
buf_state |= BM_DIRTY | BM_JUST_DIRTIED;
UnlockBufHdr(bufHdr, buf_state);
if (delayChkpt)
MyPgXact->delayChkpt = false;
if (dirtied)
{
VacuumPageDirty++;
pgBufferUsage.shared_blks_dirtied++;
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageDirty;
}
}
}
/*
* Release buffer content locks for shared buffers.
*
* Used to clean up after errors.
*
* Currently, we can expect that lwlock.c's LWLockReleaseAll() took care
* of releasing buffer content locks per se; the only thing we need to deal
* with here is clearing any PIN_COUNT request that was in progress.
*/
void
UnlockBuffers(void)
{
BufferDesc *buf = PinCountWaitBuf;
if (buf)
{
uint32 buf_state;
buf_state = LockBufHdr(buf);
/*
* Don't complain if flag bit not set; it could have been reset but we
* got a cancel/die interrupt before getting the signal.
*/
if ((buf_state & BM_PIN_COUNT_WAITER) != 0 &&
buf->wait_backend_pid == MyProcPid)
buf_state &= ~BM_PIN_COUNT_WAITER;
UnlockBufHdr(buf, buf_state);
PinCountWaitBuf = NULL;
}
}
/*
* Acquire or release the content_lock for the buffer.
*/
void
LockBuffer(Buffer buffer, int mode)
{
BufferDesc *buf;
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
return; /* local buffers need no lock */
buf = GetBufferDescriptor(buffer - 1);
if (mode == BUFFER_LOCK_UNLOCK)
ReleaseContentLock(buf);
else if (mode == BUFFER_LOCK_SHARE)
AcquireContentLock(buf, LW_SHARED);
else if (mode == BUFFER_LOCK_EXCLUSIVE)
AcquireContentLock(buf, LW_EXCLUSIVE);
else
elog(ERROR, "unrecognized buffer lock mode: %d", mode);
}
/*
* Acquire the content_lock for the buffer, but only if we don't have to wait.
*
* This assumes the caller wants BUFFER_LOCK_EXCLUSIVE mode.
*/
bool
ConditionalLockBuffer(Buffer buffer)
{
BufferDesc *buf;
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
return true; /* act as though we got it */
buf = GetBufferDescriptor(buffer - 1);
return ConditionalAcquireContentLock(buf, LW_EXCLUSIVE);
}
/*
* LockBufferForCleanup - lock a buffer in preparation for deleting items
*
* Items may be deleted from a disk page only when the caller (a) holds an
* exclusive lock on the buffer and (b) has observed that no other backend
* holds a pin on the buffer. If there is a pin, then the other backend
* might have a pointer into the buffer (for example, a heapscan reference
* to an item --- see README for more details). It's OK if a pin is added
* after the cleanup starts, however; the newly-arrived backend will be
* unable to look at the page until we release the exclusive lock.
*
* To implement this protocol, a would-be deleter must pin the buffer and
* then call LockBufferForCleanup(). LockBufferForCleanup() is similar to
* LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE), except that it loops until
* it has successfully observed pin count = 1.
*/
void
LockBufferForCleanup(Buffer buffer)
{
BufferDesc *bufHdr;
Assert(BufferIsValid(buffer));
Assert(PinCountWaitBuf == NULL);
if (BufferIsLocal(buffer))
{
/* There should be exactly one pin */
if (LocalRefCount[-buffer - 1] != 1)
elog(ERROR, "incorrect local pin count: %d",
LocalRefCount[-buffer - 1]);
/* Nobody else to wait for */
return;
}
/* There should be exactly one local pin */
if (GetPrivateRefCount(buffer) != 1)
elog(ERROR, "incorrect local pin count: %d",
GetPrivateRefCount(buffer));
bufHdr = GetBufferDescriptor(buffer - 1);
for (;;)
{
uint32 buf_state;
/* Try to acquire lock */
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
buf_state = LockBufHdr(bufHdr);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
if (BUF_STATE_GET_REFCOUNT(buf_state) == 1)
{
/* Successfully acquired exclusive lock with pincount 1 */
UnlockBufHdr(bufHdr, buf_state);
return;
}
/* Failed, so mark myself as waiting for pincount 1 */
if (buf_state & BM_PIN_COUNT_WAITER)
{
UnlockBufHdr(bufHdr, buf_state);
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
elog(ERROR, "multiple backends attempting to wait for pincount 1");
}
bufHdr->wait_backend_pid = MyProcPid;
PinCountWaitBuf = bufHdr;
buf_state |= BM_PIN_COUNT_WAITER;
UnlockBufHdr(bufHdr, buf_state);
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
/* Wait to be signaled by UnpinBuffer() */
if (InHotStandby)
{
/* Publish the bufid that Startup process waits on */
SetStartupBufferPinWaitBufId(buffer - 1);
/* Set alarm and then wait to be signaled by UnpinBuffer() */
ResolveRecoveryConflictWithBufferPin();
/* Reset the published bufid */
SetStartupBufferPinWaitBufId(-1);
}
else
ProcWaitForSignal(PG_WAIT_BUFFER_PIN);
/*
* Remove flag marking us as waiter. Normally this will not be set
* anymore, but ProcWaitForSignal() can return for other signals as
* well. We take care to only reset the flag if we're the waiter, as
* theoretically another backend could have started waiting. That's
* impossible with the current usages due to table level locking, but
* better be safe.
*/
buf_state = LockBufHdr(bufHdr);
if ((buf_state & BM_PIN_COUNT_WAITER) != 0 &&
bufHdr->wait_backend_pid == MyProcPid)
buf_state &= ~BM_PIN_COUNT_WAITER;
UnlockBufHdr(bufHdr, buf_state);
PinCountWaitBuf = NULL;
/* Loop back and try again */
}
}
/*
* Check called from RecoveryConflictInterrupt handler when Startup
* process requests cancellation of all pin holders that are blocking it.
*/
bool
HoldingBufferPinThatDelaysRecovery(void)
{
int bufid = GetStartupBufferPinWaitBufId();
/*
* If we get woken slowly then it's possible that the Startup process was
* already woken by other backends before we got here. Also possible that
* we get here by multiple interrupts or interrupts at inappropriate
* times, so make sure we do nothing if the bufid is not set.
*/
if (bufid < 0)
return false;
if (GetPrivateRefCount(bufid + 1) > 0)
return true;
return false;
}
/*
* ConditionalLockBufferForCleanup - as above, but don't wait to get the lock
*
* We won't loop, but just check once to see if the pin count is OK. If
* not, return false with no lock held.
*/
bool
ConditionalLockBufferForCleanup(Buffer buffer)
{
BufferDesc *bufHdr;
uint32 buf_state,
refcount;
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
{
refcount = LocalRefCount[-buffer - 1];
/* There should be exactly one pin */
Assert(refcount > 0);
if (refcount != 1)
return false;
/* Nobody else to wait for */
return true;
}
/* There should be exactly one local pin */
refcount = GetPrivateRefCount(buffer);
Assert(refcount);
if (refcount != 1)
return false;
/* Try to acquire lock */
if (!ConditionalLockBuffer(buffer))
return false;
bufHdr = GetBufferDescriptor(buffer - 1);
buf_state = LockBufHdr(bufHdr);
refcount = BUF_STATE_GET_REFCOUNT(buf_state);
Assert(refcount > 0);
if (refcount == 1)
{
/* Successfully acquired exclusive lock with pincount 1 */
UnlockBufHdr(bufHdr, buf_state);
return true;
}
/* Failed, so release the lock */
UnlockBufHdr(bufHdr, buf_state);
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
return false;
}
/*
* IsBufferCleanupOK - as above, but we already have the lock
*
* Check whether it's OK to perform cleanup on a buffer we've already
* locked. If we observe that the pin count is 1, our exclusive lock
* happens to be a cleanup lock, and we can proceed with anything that
* would have been allowable had we sought a cleanup lock originally.
*/
bool
IsBufferCleanupOK(Buffer buffer)
{
BufferDesc *bufHdr;
uint32 buf_state;
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
{
/* There should be exactly one pin */
if (LocalRefCount[-buffer - 1] != 1)
return false;
/* Nobody else to wait for */
return true;
}
/* There should be exactly one local pin */
if (GetPrivateRefCount(buffer) != 1)
return false;
bufHdr = GetBufferDescriptor(buffer - 1);
/* caller must hold exclusive lock on buffer */
Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
LW_EXCLUSIVE));
buf_state = LockBufHdr(bufHdr);
Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
if (BUF_STATE_GET_REFCOUNT(buf_state) == 1)
{
/* pincount is OK. */
UnlockBufHdr(bufHdr, buf_state);
return true;
}
UnlockBufHdr(bufHdr, buf_state);
return false;
}
/*
* Functions for buffer I/O handling
*
* Note: We assume that nested buffer I/O never occurs.
* i.e at most one io_in_progress lock is held per proc.
*
* Also note that these are used only for shared buffers, not local ones.
*/
/*
* WaitIO -- Block until the IO_IN_PROGRESS flag on 'buf' is cleared.
*/
static void
WaitIO(BufferDesc *buf)
{
/*
* Changed to wait until there's no IO - Inoue 01/13/2000
*
* Note this is *necessary* because an error abort in the process doing
* I/O could release the io_in_progress_lock prematurely. See
* AbortBufferIO.
*/
for (;;)
{
uint32 buf_state;
/*
* It may not be necessary to acquire the spinlock to check the flag
* here, but since this test is essential for correctness, we'd better
* play it safe.
*/
buf_state = LockBufHdr(buf);
UnlockBufHdr(buf, buf_state);
if (!(buf_state & BM_IO_IN_PROGRESS))
break;
LWLockAcquire(BufferDescriptorGetIOLock(buf), LW_SHARED);
LWLockRelease(BufferDescriptorGetIOLock(buf));
}
}
/*
* StartBufferIO: begin I/O on this buffer
* (Assumptions)
* My process is executing no IO
* The buffer is Pinned
*
* In some scenarios there are race conditions in which multiple backends
* could attempt the same I/O operation concurrently. If someone else
* has already started I/O on this buffer then we will block on the
* io_in_progress lock until he's done.
*
* Input operations are only attempted on buffers that are not BM_VALID,
* and output operations only on buffers that are BM_VALID and BM_DIRTY,
* so we can always tell if the work is already done.
*
* Returns true if we successfully marked the buffer as I/O busy,
* false if someone else already did the work.
*/
static bool
StartBufferIO(BufferDesc *buf, bool forInput)
{
uint32 buf_state;
Assert(!InProgressBuf);
for (;;)
{
/*
* Grab the io_in_progress lock so that other processes can wait for
* me to finish the I/O.
*/
LWLockAcquire(BufferDescriptorGetIOLock(buf), LW_EXCLUSIVE);
buf_state = LockBufHdr(buf);
if (!(buf_state & BM_IO_IN_PROGRESS))
break;
/*
* The only way BM_IO_IN_PROGRESS could be set when the io_in_progress
* lock isn't held is if the process doing the I/O is recovering from
* an error (see AbortBufferIO). If that's the case, we must wait for
* him to get unwedged.
*/
UnlockBufHdr(buf, buf_state);
LWLockRelease(BufferDescriptorGetIOLock(buf));
WaitIO(buf);
}
/* Once we get here, there is definitely no I/O active on this buffer */
if (forInput ? (buf_state & BM_VALID) : !(buf_state & BM_DIRTY))
{
/* someone else already did the I/O */
UnlockBufHdr(buf, buf_state);
LWLockRelease(BufferDescriptorGetIOLock(buf));
return false;
}
buf_state |= BM_IO_IN_PROGRESS;
UnlockBufHdr(buf, buf_state);
#ifdef MPROTECT_BUFFERS
BufferMProtect(buf, forInput ? PROT_WRITE|PROT_READ : PROT_READ);
#endif
InProgressBuf = buf;
IsForInput = forInput;
return true;
}
/*
* TerminateBufferIO: release a buffer we were doing I/O on
* (Assumptions)
* My process is executing IO for the buffer
* BM_IO_IN_PROGRESS bit is set for the buffer
* We hold the buffer's io_in_progress lock
* The buffer is Pinned
*
* If clear_dirty is true and BM_JUST_DIRTIED is not set, we clear the
* buffer's BM_DIRTY flag. This is appropriate when terminating a
* successful write. The check on BM_JUST_DIRTIED is necessary to avoid
* marking the buffer clean if it was re-dirtied while we were writing.
*
* set_flag_bits gets ORed into the buffer's flags. It must include
* BM_IO_ERROR in a failure case. For successful completion it could
* be 0, or BM_VALID if we just finished reading in the page.
*/
static void
TerminateBufferIO(BufferDesc *buf, bool clear_dirty, uint32 set_flag_bits)
{
uint32 buf_state;
Assert(buf == InProgressBuf);
buf_state = LockBufHdr(buf);
Assert(buf_state & BM_IO_IN_PROGRESS);
buf_state &= ~(BM_IO_IN_PROGRESS | BM_IO_ERROR);
if (clear_dirty && !(buf_state & BM_JUST_DIRTIED))
buf_state &= ~(BM_DIRTY | BM_CHECKPOINT_NEEDED);
buf_state |= set_flag_bits;
UnlockBufHdr(buf, buf_state);
InProgressBuf = NULL;
#ifdef MPROTECT_BUFFERS
/* XXX: should this be PROT_NONE if called from AbortBufferIO? */
if (!LWLockHeldByMe(BufferDescriptorGetContentLock(buf)))
BufferMProtect(buf, PROT_READ);
#endif
LWLockRelease(BufferDescriptorGetIOLock(buf));
}
/*
* AbortBufferIO: Clean up any active buffer I/O after an error.
*
* All LWLocks we might have held have been released,
* but we haven't yet released buffer pins, so the buffer is still pinned.
*
* If I/O was in progress, we always set BM_IO_ERROR, even though it's
* possible the error condition wasn't related to the I/O.
*/
void
AbortBufferIO(void)
{
BufferDesc *buf = InProgressBuf;
if (buf)
{
uint32 buf_state;
/*
* Since LWLockReleaseAll has already been called, we're not holding
* the buffer's io_in_progress_lock. We have to re-acquire it so that
* we can use TerminateBufferIO. Anyone who's executing WaitIO on the
* buffer will be in a busy spin until we succeed in doing this.
*/
LWLockAcquire(BufferDescriptorGetIOLock(buf), LW_EXCLUSIVE);
buf_state = LockBufHdr(buf);
Assert(buf_state & BM_IO_IN_PROGRESS);
if (IsForInput)
{
Assert(!(buf_state & BM_DIRTY));
/* We'd better not think buffer is valid yet */
Assert(!(buf_state & BM_VALID));
UnlockBufHdr(buf, buf_state);
}
else
{
Assert(buf_state & BM_DIRTY);
UnlockBufHdr(buf, buf_state);
/* Issue notice if this is not the first failure... */
if (buf_state & BM_IO_ERROR)
{
/* Buffer is pinned, so we can read tag without spinlock */
char *path;
path = relpathbackend(buf->tag.rnode,
(buf_state & BM_TEMP) ?
TempRelBackendId : InvalidBackendId,
buf->tag.forkNum);
ereport(WARNING,
(errcode(ERRCODE_IO_ERROR),
errmsg("could not write block %u of %s",
buf->tag.blockNum, path),
errdetail("Multiple failures --- write error might be permanent.")));
pfree(path);
}
}
TerminateBufferIO(buf, false, BM_IO_ERROR);
}
}
/*
* Error context callback for errors occurring during shared buffer writes.
*/
static void
shared_buffer_write_error_callback(void *arg)
{
BufferDesc *bufHdr = (BufferDesc *) arg;
/* Buffer is pinned, so we can read the tag without locking the spinlock */
if (bufHdr != NULL)
{
uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
char *path = relpathbackend(bufHdr->tag.rnode,
(buf_state & BM_TEMP) ?
TempRelBackendId : InvalidBackendId,
bufHdr->tag.forkNum);
errcontext("writing block %u of relation %s",
bufHdr->tag.blockNum, path);
pfree(path);
}
}
/*
* Error context callback for errors occurring during local buffer writes.
*/
static void
local_buffer_write_error_callback(void *arg)
{
BufferDesc *bufHdr = (BufferDesc *) arg;
if (bufHdr != NULL)
{
char *path = relpathbackend(bufHdr->tag.rnode, MyBackendId,
bufHdr->tag.forkNum);
errcontext("writing block %u of relation %s",
bufHdr->tag.blockNum, path);
pfree(path);
}
}
/*
* RelFileNode qsort/bsearch comparator; see RelFileNodeEquals.
*/
static int
rnode_comparator(const void *p1, const void *p2)
{
RelFileNode n1 = *(const RelFileNode *) p1;
RelFileNode n2 = *(const RelFileNode *) p2;
if (n1.relNode < n2.relNode)
return -1;
else if (n1.relNode > n2.relNode)
return 1;
if (n1.dbNode < n2.dbNode)
return -1;
else if (n1.dbNode > n2.dbNode)
return 1;
if (n1.spcNode < n2.spcNode)
return -1;
else if (n1.spcNode > n2.spcNode)
return 1;
else
return 0;
}
/*
* Lock buffer header - set BM_LOCKED in buffer state.
*/
uint32
LockBufHdr(BufferDesc *desc)
{
SpinDelayStatus delayStatus;
uint32 old_buf_state;
init_local_spin_delay(&delayStatus);
while (true)
{
/* set BM_LOCKED flag */
old_buf_state = pg_atomic_fetch_or_u32(&desc->state, BM_LOCKED);
/* if it wasn't set before we're OK */
if (!(old_buf_state & BM_LOCKED))
break;
perform_spin_delay(&delayStatus);
}
finish_spin_delay(&delayStatus);
return old_buf_state | BM_LOCKED;
}
/*
* Wait until the BM_LOCKED flag isn't set anymore and return the buffer's
* state at that point.
*
* Obviously the buffer could be locked by the time the value is returned, so
* this is primarily useful in CAS style loops.
*/
static uint32
WaitBufHdrUnlocked(BufferDesc *buf)
{
SpinDelayStatus delayStatus;
uint32 buf_state;
init_local_spin_delay(&delayStatus);
buf_state = pg_atomic_read_u32(&buf->state);
while (buf_state & BM_LOCKED)
{
perform_spin_delay(&delayStatus);
buf_state = pg_atomic_read_u32(&buf->state);
}
finish_spin_delay(&delayStatus);
return buf_state;
}
/*
* BufferTag comparator.
*/
static int
buffertag_comparator(const void *a, const void *b)
{
const BufferTag *ba = (const BufferTag *) a;
const BufferTag *bb = (const BufferTag *) b;
int ret;
ret = rnode_comparator(&ba->rnode, &bb->rnode);
if (ret != 0)
return ret;
if (ba->forkNum < bb->forkNum)
return -1;
if (ba->forkNum > bb->forkNum)
return 1;
if (ba->blockNum < bb->blockNum)
return -1;
if (ba->blockNum > bb->blockNum)
return 1;
return 0;
}
/*
* Comparator determining the writeout order in a checkpoint.
*
* It is important that tablespaces are compared first, the logic balancing
* writes between tablespaces relies on it.
*/
static int
ckpt_buforder_comparator(const void *pa, const void *pb)
{
const CkptSortItem *a = (const CkptSortItem *) pa;
const CkptSortItem *b = (const CkptSortItem *) pb;
/* compare tablespace */
if (a->tsId < b->tsId)
return -1;
else if (a->tsId > b->tsId)
return 1;
/* compare relation */
if (a->relNode < b->relNode)
return -1;
else if (a->relNode > b->relNode)
return 1;
/* compare fork */
else if (a->forkNum < b->forkNum)
return -1;
else if (a->forkNum > b->forkNum)
return 1;
/* compare block number */
else if (a->blockNum < b->blockNum)
return -1;
else if (a->blockNum > b->blockNum)
return 1;
/* equal page IDs are unlikely, but not impossible */
return 0;
}
/*
* Comparator for a Min-Heap over the per-tablespace checkpoint completion
* progress.
*/
static int
ts_ckpt_progress_comparator(Datum a, Datum b, void *arg)
{
CkptTsStatus *sa = (CkptTsStatus *) a;
CkptTsStatus *sb = (CkptTsStatus *) b;
/* we want a min-heap, so return 1 for the a < b */
if (sa->progress < sb->progress)
return 1;
else if (sa->progress == sb->progress)
return 0;
else
return -1;
}
/*
* Initialize a writeback context, discarding potential previous state.
*
* *max_pending is a pointer instead of an immediate value, so the coalesce
* limits can easily changed by the GUC mechanism, and so calling code does
* not have to check the current configuration. A value is 0 means that no
* writeback control will be performed.
*/
void
WritebackContextInit(WritebackContext *context, int *max_pending)
{
Assert(*max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
context->max_pending = max_pending;
context->nr_pending = 0;
}
/*
* Add buffer to list of pending writeback requests.
*/
void
ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
{
PendingWriteback *pending;
/*
* Add buffer to the pending writeback array, unless writeback control is
* disabled.
*/
if (*context->max_pending > 0)
{
Assert(*context->max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
pending = &context->pending_writebacks[context->nr_pending++];
pending->tag = *tag;
}
/*
* Perform pending flushes if the writeback limit is exceeded. This
* includes the case where previously an item has been added, but control
* is now disabled.
*/
if (context->nr_pending >= *context->max_pending)
IssuePendingWritebacks(context);
}
/*
* Issue all pending writeback requests, previously scheduled with
* ScheduleBufferTagForWriteback, to the OS.
*
* Because this is only used to improve the OSs IO scheduling we try to never
* error out - it's just a hint.
*/
void
IssuePendingWritebacks(WritebackContext *context)
{
int i;
if (context->nr_pending == 0)
return;
/*
* Executing the writes in-order can make them a lot faster, and allows to
* merge writeback requests to consecutive blocks into larger writebacks.
*/
qsort(&context->pending_writebacks, context->nr_pending,
sizeof(PendingWriteback), buffertag_comparator);
/*
* Coalesce neighbouring writes, but nothing else. For that we iterate
* through the, now sorted, array of pending flushes, and look forward to
* find all neighbouring (or identical) writes.
*/
for (i = 0; i < context->nr_pending; i++)
{
PendingWriteback *cur;
PendingWriteback *next;
SMgrRelation reln;
int ahead;
BufferTag tag;
Size nblocks = 1;
cur = &context->pending_writebacks[i];
tag = cur->tag;
/*
* Peek ahead, into following writeback requests, to see if they can
* be combined with the current one.
*/
for (ahead = 0; i + ahead + 1 < context->nr_pending; ahead++)
{
next = &context->pending_writebacks[i + ahead + 1];
/* different file, stop */
if (!RelFileNodeEquals(cur->tag.rnode, next->tag.rnode) ||
cur->tag.forkNum != next->tag.forkNum)
break;
/* ok, block queued twice, skip */
if (cur->tag.blockNum == next->tag.blockNum)
continue;
/* only merge consecutive writes */
if (cur->tag.blockNum + 1 != next->tag.blockNum)
break;
nblocks++;
cur = next;
}
i += ahead;
/* and finally tell the kernel to write the data to storage */
reln = smgropen(tag.rnode, InvalidBackendId, 0);
smgrwriteback(reln, tag.forkNum, tag.blockNum, nblocks);
}
context->nr_pending = 0;
}
/*
* Implement slower/larger portions of TestForOldSnapshot
*
* Smaller/faster portions are put inline, but the entire set of logic is too
* big for that.
*/
void
TestForOldSnapshot_impl(Snapshot snapshot, Relation relation)
{
if (RelationAllowsEarlyPruning(relation)
&& (snapshot)->whenTaken < GetOldSnapshotThresholdTimestamp())
ereport(ERROR,
(errcode(ERRCODE_SNAPSHOT_TOO_OLD),
errmsg("snapshot too old")));
}
/* This is used by PageGetLSN(). */
#ifdef USE_ASSERT_CHECKING
bool
BufferLockHeldByMe(Page page)
{
char *pagePtr = page;
/*
* We only want to assert that we hold a lock on the page contents if the
* page is shared (i.e. it is one of the BufferBlocks).
*/
if (BufferBlocks <= pagePtr &&
pagePtr < (BufferBlocks + NBuffers * BLCKSZ))
{
BufferDesc *hdr = GetBufferDescriptor((pagePtr - BufferBlocks) / BLCKSZ);
return LWLockHeldByMe(BufferDescriptorGetContentLock(hdr));
}
return true;
}
#endif
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