greenplumn rewriteheap 源码
greenplumn rewriteheap 代码
文件路径：/src/backend/access/heap/rewriteheap.c
/*-------------------------------------------------------------------------
*
* rewriteheap.c
* Support functions to rewrite tables.
*
* These functions provide a facility to completely rewrite a heap, while
* preserving visibility information and update chains.
*
* INTERFACE
*
* The caller is responsible for creating the new heap, all catalog
* changes, supplying the tuples to be written to the new heap, and
* rebuilding indexes. The caller must hold AccessExclusiveLock on the
* target table, because we assume no one else is writing into it.
*
* To use the facility:
*
* begin_heap_rewrite
* while (fetch next tuple)
* {
* if (tuple is dead)
* rewrite_heap_dead_tuple
* else
* {
* // do any transformations here if required
* rewrite_heap_tuple
* }
* }
* end_heap_rewrite
*
* The contents of the new relation shouldn't be relied on until after
* end_heap_rewrite is called.
*
*
* IMPLEMENTATION
*
* This would be a fairly trivial affair, except that we need to maintain
* the ctid chains that link versions of an updated tuple together.
* Since the newly stored tuples will have tids different from the original
* ones, if we just copied t_ctid fields to the new table the links would
* be wrong. When we are required to copy a (presumably recently-dead or
* delete-in-progress) tuple whose ctid doesn't point to itself, we have
* to substitute the correct ctid instead.
*
* For each ctid reference from A -> B, we might encounter either A first
* or B first. (Note that a tuple in the middle of a chain is both A and B
* of different pairs.)
*
* If we encounter A first, we'll store the tuple in the unresolved_tups
* hash table. When we later encounter B, we remove A from the hash table,
* fix the ctid to point to the new location of B, and insert both A and B
* to the new heap.
*
* If we encounter B first, we can insert B to the new heap right away.
* We then add an entry to the old_new_tid_map hash table showing B's
* original tid (in the old heap) and new tid (in the new heap).
* When we later encounter A, we get the new location of B from the table,
* and can write A immediately with the correct ctid.
*
* Entries in the hash tables can be removed as soon as the later tuple
* is encountered. That helps to keep the memory usage down. At the end,
* both tables are usually empty; we should have encountered both A and B
* of each pair. However, it's possible for A to be RECENTLY_DEAD and B
* entirely DEAD according to HeapTupleSatisfiesVacuum, because the test
* for deadness using OldestXmin is not exact. In such a case we might
* encounter B first, and skip it, and find A later. Then A would be added
* to unresolved_tups, and stay there until end of the rewrite. Since
* this case is very unusual, we don't worry about the memory usage.
*
* Using in-memory hash tables means that we use some memory for each live
* update chain in the table, from the time we find one end of the
* reference until we find the other end. That shouldn't be a problem in
* practice, but if you do something like an UPDATE without a where-clause
* on a large table, and then run CLUSTER in the same transaction, you
* could run out of memory. It doesn't seem worthwhile to add support for
* spill-to-disk, as there shouldn't be that many RECENTLY_DEAD tuples in a
* table under normal circumstances. Furthermore, in the typical scenario
* of CLUSTERing on an unchanging key column, we'll see all the versions
* of a given tuple together anyway, and so the peak memory usage is only
* proportional to the number of RECENTLY_DEAD versions of a single row, not
* in the whole table. Note that if we do fail halfway through a CLUSTER,
* the old table is still valid, so failure is not catastrophic.
*
* We can't use the normal heap_insert function to insert into the new
* heap, because heap_insert overwrites the visibility information.
* We use a special-purpose raw_heap_insert function instead, which
* is optimized for bulk inserting a lot of tuples, knowing that we have
* exclusive access to the heap. raw_heap_insert builds new pages in
* local storage. When a page is full, or at the end of the process,
* we insert it to WAL as a single record and then write it to disk
* directly through smgr. Note, however, that any data sent to the new
* heap's TOAST table will go through the normal bufmgr.
*
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994-5, Regents of the University of California
*
* IDENTIFICATION
* src/backend/access/heap/rewriteheap.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <sys/stat.h>
#include <unistd.h>
#include "miscadmin.h"
#include "access/heapam.h"
#include "access/heapam_xlog.h"
#include "access/rewriteheap.h"
#include "access/transam.h"
#include "access/tuptoaster.h"
#include "access/xact.h"
#include "access/xloginsert.h"
#include "catalog/catalog.h"
#include "lib/ilist.h"
#include "pgstat.h"
#include "replication/logical.h"
#include "replication/slot.h"
#include "storage/bufmgr.h"
#include "storage/fd.h"
#include "storage/smgr.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "storage/procarray.h"
/*
* State associated with a rewrite operation. This is opaque to the user
* of the rewrite facility.
*/
typedef struct RewriteStateData
{
Relation rs_old_rel; /* source heap */
Relation rs_new_rel; /* destination heap */
Page rs_buffer; /* page currently being built */
BlockNumber rs_blockno; /* block where page will go */
bool rs_buffer_valid; /* T if any tuples in buffer */
bool rs_use_wal; /* must we WAL-log inserts? */
bool rs_logical_rewrite; /* do we need to do logical rewriting */
TransactionId rs_oldest_xmin; /* oldest xmin used by caller to determine
* tuple visibility */
TransactionId rs_freeze_xid; /* Xid that will be used as freeze cutoff
* point */
TransactionId rs_logical_xmin; /* Xid that will be used as cutoff point
* for logical rewrites */
MultiXactId rs_cutoff_multi; /* MultiXactId that will be used as cutoff
* point for multixacts */
MemoryContext rs_cxt; /* for hash tables and entries and tuples in
* them */
XLogRecPtr rs_begin_lsn; /* XLogInsertLsn when starting the rewrite */
HTAB *rs_unresolved_tups; /* unmatched A tuples */
HTAB *rs_old_new_tid_map; /* unmatched B tuples */
HTAB *rs_logical_mappings; /* logical remapping files */
uint32 rs_num_rewrite_mappings; /* # in memory mappings */
} RewriteStateData;
/*
* The lookup keys for the hash tables are tuple TID and xmin (we must check
* both to avoid false matches from dead tuples). Beware that there is
* probably some padding space in this struct; it must be zeroed out for
* correct hashtable operation.
*/
typedef struct
{
TransactionId xmin; /* tuple xmin */
ItemPointerData tid; /* tuple location in old heap */
} TidHashKey;
/*
* Entry structures for the hash tables
*/
typedef struct
{
TidHashKey key; /* expected xmin/old location of B tuple */
ItemPointerData old_tid; /* A's location in the old heap */
HeapTuple tuple; /* A's tuple contents */
} UnresolvedTupData;
typedef UnresolvedTupData *UnresolvedTup;
typedef struct
{
TidHashKey key; /* actual xmin/old location of B tuple */
ItemPointerData new_tid; /* where we put it in the new heap */
} OldToNewMappingData;
typedef OldToNewMappingData *OldToNewMapping;
/*
* In-Memory data for an xid that might need logical remapping entries
* to be logged.
*/
typedef struct RewriteMappingFile
{
TransactionId xid; /* xid that might need to see the row */
int vfd; /* fd of mappings file */
off_t off; /* how far have we written yet */
uint32 num_mappings; /* number of in-memory mappings */
dlist_head mappings; /* list of in-memory mappings */
char path[MAXPGPATH]; /* path, for error messages */
} RewriteMappingFile;
/*
* A single In-Memory logical rewrite mapping, hanging off
* RewriteMappingFile->mappings.
*/
typedef struct RewriteMappingDataEntry
{
LogicalRewriteMappingData map; /* map between old and new location of the
* tuple */
dlist_node node;
} RewriteMappingDataEntry;
/* prototypes for internal functions */
static void raw_heap_insert(RewriteState state, HeapTuple tup);
/* internal logical remapping prototypes */
static void logical_begin_heap_rewrite(RewriteState state);
static void logical_rewrite_heap_tuple(RewriteState state, ItemPointerData old_tid, HeapTuple new_tuple);
static void logical_end_heap_rewrite(RewriteState state);
/*
* Begin a rewrite of a table
*
* old_heap old, locked heap relation tuples will be read from
* new_heap new, locked heap relation to insert tuples to
* oldest_xmin xid used by the caller to determine which tuples are dead
* freeze_xid xid before which tuples will be frozen
* min_multi multixact before which multis will be removed
* use_wal should the inserts to the new heap be WAL-logged?
*
* Returns an opaque RewriteState, allocated in current memory context,
* to be used in subsequent calls to the other functions.
*/
RewriteState
begin_heap_rewrite(Relation old_heap, Relation new_heap, TransactionId oldest_xmin,
TransactionId freeze_xid, MultiXactId cutoff_multi,
bool use_wal)
{
RewriteState state;
MemoryContext rw_cxt;
MemoryContext old_cxt;
HASHCTL hash_ctl;
/*
* To ease cleanup, make a separate context that will contain the
* RewriteState struct itself plus all subsidiary data.
*/
rw_cxt = AllocSetContextCreate(CurrentMemoryContext,
"Table rewrite",
ALLOCSET_DEFAULT_SIZES);
old_cxt = MemoryContextSwitchTo(rw_cxt);
/* Create and fill in the state struct */
state = palloc0(sizeof(RewriteStateData));
state->rs_old_rel = old_heap;
state->rs_new_rel = new_heap;
state->rs_buffer = (Page) palloc(BLCKSZ);
/* new_heap needn't be empty, just locked */
state->rs_blockno = AcquireNumberOfBlocks(new_heap);
state->rs_buffer_valid = false;
state->rs_use_wal = use_wal;
state->rs_oldest_xmin = oldest_xmin;
state->rs_freeze_xid = freeze_xid;
state->rs_cutoff_multi = cutoff_multi;
state->rs_cxt = rw_cxt;
/* Initialize hash tables used to track update chains */
memset(&hash_ctl, 0, sizeof(hash_ctl));
hash_ctl.keysize = sizeof(TidHashKey);
hash_ctl.entrysize = sizeof(UnresolvedTupData);
hash_ctl.hcxt = state->rs_cxt;
state->rs_unresolved_tups =
hash_create("Rewrite / Unresolved ctids",
128, /* arbitrary initial size */
&hash_ctl,
HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
hash_ctl.entrysize = sizeof(OldToNewMappingData);
state->rs_old_new_tid_map =
hash_create("Rewrite / Old to new tid map",
128, /* arbitrary initial size */
&hash_ctl,
HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
MemoryContextSwitchTo(old_cxt);
logical_begin_heap_rewrite(state);
return state;
}
/*
* End a rewrite.
*
* state and any other resources are freed.
*/
void
end_heap_rewrite(RewriteState state)
{
HASH_SEQ_STATUS seq_status;
UnresolvedTup unresolved;
/*
* Write any remaining tuples in the UnresolvedTups table. If we have any
* left, they should in fact be dead, but let's err on the safe side.
*/
hash_seq_init(&seq_status, state->rs_unresolved_tups);
while ((unresolved = hash_seq_search(&seq_status)) != NULL)
{
ItemPointerSetInvalid(&unresolved->tuple->t_data->t_ctid);
raw_heap_insert(state, unresolved->tuple);
}
/* Write the last page, if any */
if (state->rs_buffer_valid)
{
if (state->rs_use_wal)
log_newpage(&state->rs_new_rel->rd_node,
MAIN_FORKNUM,
state->rs_blockno,
state->rs_buffer,
true);
RelationOpenSmgr(state->rs_new_rel);
PageSetChecksumInplace(state->rs_buffer, state->rs_blockno);
smgrextend(state->rs_new_rel->rd_smgr, MAIN_FORKNUM, state->rs_blockno,
(char *) state->rs_buffer, true);
}
/*
* If the rel is WAL-logged, must fsync before commit. We use heap_sync
* to ensure that the toast table gets fsync'd too.
*
* It's obvious that we must do this when not WAL-logging. It's less
* obvious that we have to do it even if we did WAL-log the pages. The
* reason is the same as in storage.c's RelationCopyStorage(): we're
* writing data that's not in shared buffers, and so a CHECKPOINT
* occurring during the rewriteheap operation won't have fsync'd data we
* wrote before the checkpoint.
*/
if (RelationNeedsWAL(state->rs_new_rel))
heap_sync(state->rs_new_rel);
logical_end_heap_rewrite(state);
/* Deleting the context frees everything */
MemoryContextDelete(state->rs_cxt);
}
/*
* Add a tuple to the new heap.
*
* Visibility information is copied from the original tuple, except that
* we "freeze" very-old tuples. Note that since we scribble on new_tuple,
* it had better be temp storage not a pointer to the original tuple.
*
* state opaque state as returned by begin_heap_rewrite
* old_tuple original tuple in the old heap
* new_tuple new, rewritten tuple to be inserted to new heap
*/
void
rewrite_heap_tuple(RewriteState state,
HeapTuple old_tuple, HeapTuple new_tuple)
{
MemoryContext old_cxt;
ItemPointerData old_tid;
TidHashKey hashkey;
bool found;
bool free_new;
old_cxt = MemoryContextSwitchTo(state->rs_cxt);
/*
* Copy the original tuple's visibility information into new_tuple.
*
* XXX we might later need to copy some t_infomask2 bits, too? Right now,
* we intentionally clear the HOT status bits.
*/
memcpy(&new_tuple->t_data->t_choice.t_heap,
&old_tuple->t_data->t_choice.t_heap,
sizeof(HeapTupleFields));
new_tuple->t_data->t_infomask &= ~HEAP_XACT_MASK;
new_tuple->t_data->t_infomask2 &= ~HEAP2_XACT_MASK;
new_tuple->t_data->t_infomask |=
old_tuple->t_data->t_infomask & HEAP_XACT_MASK;
/*
* While we have our hands on the tuple, we may as well freeze any
* eligible xmin or xmax, so that future VACUUM effort can be saved.
*/
heap_freeze_tuple(new_tuple->t_data,
state->rs_old_rel->rd_rel->relfrozenxid,
state->rs_old_rel->rd_rel->relminmxid,
state->rs_freeze_xid,
state->rs_cutoff_multi);
/*
* Invalid ctid means that ctid should point to the tuple itself. We'll
* override it later if the tuple is part of an update chain.
*/
ItemPointerSetInvalid(&new_tuple->t_data->t_ctid);
/*
* If the tuple has been updated, check the old-to-new mapping hash table.
*/
if (!((old_tuple->t_data->t_infomask & HEAP_XMAX_INVALID) ||
HeapTupleHeaderIsOnlyLocked(old_tuple->t_data)) &&
!HeapTupleHeaderIndicatesMovedPartitions(old_tuple->t_data) &&
!(ItemPointerEquals(&(old_tuple->t_self),
&(old_tuple->t_data->t_ctid))))
{
OldToNewMapping mapping;
memset(&hashkey, 0, sizeof(hashkey));
hashkey.xmin = HeapTupleHeaderGetUpdateXid(old_tuple->t_data);
hashkey.tid = old_tuple->t_data->t_ctid;
mapping = (OldToNewMapping)
hash_search(state->rs_old_new_tid_map, &hashkey,
HASH_FIND, NULL);
if (mapping != NULL)
{
/*
* We've already copied the tuple that t_ctid points to, so we can
* set the ctid of this tuple to point to the new location, and
* insert it right away.
*/
new_tuple->t_data->t_ctid = mapping->new_tid;
/* We don't need the mapping entry anymore */
hash_search(state->rs_old_new_tid_map, &hashkey,
HASH_REMOVE, &found);
Assert(found);
}
else
{
/*
* We haven't seen the tuple t_ctid points to yet. Stash this
* tuple into unresolved_tups to be written later.
*/
UnresolvedTup unresolved;
unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
HASH_ENTER, &found);
Assert(!found);
unresolved->old_tid = old_tuple->t_self;
unresolved->tuple = heap_copytuple(new_tuple);
/*
* We can't do anything more now, since we don't know where the
* tuple will be written.
*/
MemoryContextSwitchTo(old_cxt);
return;
}
}
/*
* Now we will write the tuple, and then check to see if it is the B tuple
* in any new or known pair. When we resolve a known pair, we will be
* able to write that pair's A tuple, and then we have to check if it
* resolves some other pair. Hence, we need a loop here.
*/
old_tid = old_tuple->t_self;
free_new = false;
for (;;)
{
ItemPointerData new_tid;
/* Insert the tuple and find out where it's put in new_heap */
raw_heap_insert(state, new_tuple);
new_tid = new_tuple->t_self;
logical_rewrite_heap_tuple(state, old_tid, new_tuple);
/*
* If the tuple is the updated version of a row, and the prior version
* wouldn't be DEAD yet, then we need to either resolve the prior
* version (if it's waiting in rs_unresolved_tups), or make an entry
* in rs_old_new_tid_map (so we can resolve it when we do see it). The
* previous tuple's xmax would equal this one's xmin, so it's
* RECENTLY_DEAD if and only if the xmin is not before OldestXmin.
*/
if ((new_tuple->t_data->t_infomask & HEAP_UPDATED) &&
!TransactionIdPrecedes(HeapTupleHeaderGetXmin(new_tuple->t_data),
state->rs_oldest_xmin))
{
/*
* Okay, this is B in an update pair. See if we've seen A.
*/
UnresolvedTup unresolved;
memset(&hashkey, 0, sizeof(hashkey));
hashkey.xmin = HeapTupleHeaderGetXmin(new_tuple->t_data);
hashkey.tid = old_tid;
unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
HASH_FIND, NULL);
if (unresolved != NULL)
{
/*
* We have seen and memorized the previous tuple already. Now
* that we know where we inserted the tuple its t_ctid points
* to, fix its t_ctid and insert it to the new heap.
*/
if (free_new)
heap_freetuple(new_tuple);
new_tuple = unresolved->tuple;
free_new = true;
old_tid = unresolved->old_tid;
new_tuple->t_data->t_ctid = new_tid;
/*
* We don't need the hash entry anymore, but don't free its
* tuple just yet.
*/
hash_search(state->rs_unresolved_tups, &hashkey,
HASH_REMOVE, &found);
Assert(found);
/* loop back to insert the previous tuple in the chain */
continue;
}
else
{
/*
* Remember the new tid of this tuple. We'll use it to set the
* ctid when we find the previous tuple in the chain.
*/
OldToNewMapping mapping;
mapping = hash_search(state->rs_old_new_tid_map, &hashkey,
HASH_ENTER, &found);
Assert(!found);
mapping->new_tid = new_tid;
}
}
/* Done with this (chain of) tuples, for now */
if (free_new)
heap_freetuple(new_tuple);
break;
}
MemoryContextSwitchTo(old_cxt);
}
/*
* Register a dead tuple with an ongoing rewrite. Dead tuples are not
* copied to the new table, but we still make note of them so that we
* can release some resources earlier.
*
* Returns true if a tuple was removed from the unresolved_tups table.
* This indicates that that tuple, previously thought to be "recently dead",
* is now known really dead and won't be written to the output.
*/
bool
rewrite_heap_dead_tuple(RewriteState state, HeapTuple old_tuple)
{
/*
* If we have already seen an earlier tuple in the update chain that
* points to this tuple, let's forget about that earlier tuple. It's in
* fact dead as well, our simple xmax < OldestXmin test in
* HeapTupleSatisfiesVacuum just wasn't enough to detect it. It happens
* when xmin of a tuple is greater than xmax, which sounds
* counter-intuitive but is perfectly valid.
*
* We don't bother to try to detect the situation the other way round,
* when we encounter the dead tuple first and then the recently dead one
* that points to it. If that happens, we'll have some unmatched entries
* in the UnresolvedTups hash table at the end. That can happen anyway,
* because a vacuum might have removed the dead tuple in the chain before
* us.
*/
UnresolvedTup unresolved;
TidHashKey hashkey;
bool found;
memset(&hashkey, 0, sizeof(hashkey));
hashkey.xmin = HeapTupleHeaderGetXmin(old_tuple->t_data);
hashkey.tid = old_tuple->t_self;
unresolved = hash_search(state->rs_unresolved_tups, &hashkey,
HASH_FIND, NULL);
if (unresolved != NULL)
{
/* Need to free the contained tuple as well as the hashtable entry */
heap_freetuple(unresolved->tuple);
hash_search(state->rs_unresolved_tups, &hashkey,
HASH_REMOVE, &found);
Assert(found);
return true;
}
return false;
}
/*
* Insert a tuple to the new relation. This has to track heap_insert
* and its subsidiary functions!
*
* t_self of the tuple is set to the new TID of the tuple. If t_ctid of the
* tuple is invalid on entry, it's replaced with the new TID as well (in
* the inserted data only, not in the caller's copy).
*/
static void
raw_heap_insert(RewriteState state, HeapTuple tup)
{
Page page = state->rs_buffer;
Size pageFreeSpace,
saveFreeSpace;
Size len;
OffsetNumber newoff;
HeapTuple heaptup;
/*
* If the new tuple is too big for storage or contains already toasted
* out-of-line attributes from some other relation, invoke the toaster.
*
* Note: below this point, heaptup is the data we actually intend to store
* into the relation; tup is the caller's original untoasted data.
*/
if (state->rs_new_rel->rd_rel->relkind == RELKIND_TOASTVALUE)
{
/* toast table entries should never be recursively toasted */
Assert(!HeapTupleHasExternal(tup));
heaptup = tup;
}
else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD)
{
int options = HEAP_INSERT_SKIP_FSM;
if (!state->rs_use_wal)
options |= HEAP_INSERT_SKIP_WAL;
/*
* While rewriting the heap for VACUUM FULL / CLUSTER, make sure data
* for the TOAST table are not logically decoded. The main heap is
* WAL-logged as XLOG FPI records, which are not logically decoded.
*/
options |= HEAP_INSERT_NO_LOGICAL;
heaptup = toast_insert_or_update(state->rs_new_rel, tup, NULL,
TOAST_TUPLE_TARGET,
false,
options);
}
else
heaptup = tup;
len = MAXALIGN(heaptup->t_len); /* be conservative */
/*
* If we're gonna fail for oversize tuple, do it right away
*/
if (len > MaxHeapTupleSize)
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("row is too big: size %zu, maximum size %zu",
len, MaxHeapTupleSize)));
/* Compute desired extra freespace due to fillfactor option */
saveFreeSpace = RelationGetTargetPageFreeSpace(state->rs_new_rel,
HEAP_DEFAULT_FILLFACTOR);
/* Now we can check to see if there's enough free space already. */
if (state->rs_buffer_valid)
{
pageFreeSpace = PageGetHeapFreeSpace(page);
if (len + saveFreeSpace > pageFreeSpace)
{
/* Doesn't fit, so write out the existing page */
/* XLOG stuff */
if (state->rs_use_wal)
log_newpage(&state->rs_new_rel->rd_node,
MAIN_FORKNUM,
state->rs_blockno,
page,
true);
/*
* Now write the page. We say isTemp = true even if it's not a
* temp table, because there's no need for smgr to schedule an
* fsync for this write; we'll do it ourselves in
* end_heap_rewrite.
*/
RelationOpenSmgr(state->rs_new_rel);
PageSetChecksumInplace(page, state->rs_blockno);
smgrextend(state->rs_new_rel->rd_smgr, MAIN_FORKNUM,
state->rs_blockno, (char *) page, true);
state->rs_blockno++;
state->rs_buffer_valid = false;
if (state->rs_use_wal)
wait_to_avoid_large_repl_lag();
}
}
if (!state->rs_buffer_valid)
{
/* Initialize a new empty page */
PageInit(page, BLCKSZ, 0);
state->rs_buffer_valid = true;
}
/* And now we can insert the tuple into the page */
newoff = PageAddItem(page, (Item) heaptup->t_data, heaptup->t_len,
InvalidOffsetNumber, false, true);
if (newoff == InvalidOffsetNumber)
elog(ERROR, "failed to add tuple");
/* Update caller's t_self to the actual position where it was stored */
ItemPointerSet(&(tup->t_self), state->rs_blockno, newoff);
/*
* Insert the correct position into CTID of the stored tuple, too, if the
* caller didn't supply a valid CTID.
*/
if (!ItemPointerIsValid(&tup->t_data->t_ctid))
{
ItemId newitemid;
HeapTupleHeader onpage_tup;
newitemid = PageGetItemId(page, newoff);
onpage_tup = (HeapTupleHeader) PageGetItem(page, newitemid);
onpage_tup->t_ctid = tup->t_self;
}
/* If heaptup is a private copy, release it. */
if (heaptup != tup)
heap_freetuple(heaptup);
}
/* ------------------------------------------------------------------------
* Logical rewrite support
*
* When doing logical decoding - which relies on using cmin/cmax of catalog
* tuples, via xl_heap_new_cid records - heap rewrites have to log enough
* information to allow the decoding backend to updates its internal mapping
* of (relfilenode,ctid) => (cmin, cmax) to be correct for the rewritten heap.
*
* For that, every time we find a tuple that's been modified in a catalog
* relation within the xmin horizon of any decoding slot, we log a mapping
* from the old to the new location.
*
* To deal with rewrites that abort the filename of a mapping file contains
* the xid of the transaction performing the rewrite, which then can be
* checked before being read in.
*
* For efficiency we don't immediately spill every single map mapping for a
* row to disk but only do so in batches when we've collected several of them
* in memory or when end_heap_rewrite() has been called.
*
* Crash-Safety: This module diverts from the usual patterns of doing WAL
* since it cannot rely on checkpoint flushing out all buffers and thus
* waiting for exclusive locks on buffers. Usually the XLogInsert() covering
* buffer modifications is performed while the buffer(s) that are being
* modified are exclusively locked guaranteeing that both the WAL record and
* the modified heap are on either side of the checkpoint. But since the
* mapping files we log aren't in shared_buffers that interlock doesn't work.
*
* Instead we simply write the mapping files out to disk, *before* the
* XLogInsert() is performed. That guarantees that either the XLogInsert() is
* inserted after the checkpoint's redo pointer or that the checkpoint (via
* LogicalRewriteHeapCheckpoint()) has flushed the (partial) mapping file to
* disk. That leaves the tail end that has not yet been flushed open to
* corruption, which is solved by including the current offset in the
* xl_heap_rewrite_mapping records and truncating the mapping file to it
* during replay. Every time a rewrite is finished all generated mapping files
* are synced to disk.
*
* Note that if we were only concerned about crash safety we wouldn't have to
* deal with WAL logging at all - an fsync() at the end of a rewrite would be
* sufficient for crash safety. Any mapping that hasn't been safely flushed to
* disk has to be by an aborted (explicitly or via a crash) transaction and is
* ignored by virtue of the xid in its name being subject to a
* TransactionDidCommit() check. But we want to support having standbys via
* physical replication, both for availability and to do logical decoding
* there.
* ------------------------------------------------------------------------
*/
/*
* Do preparations for logging logical mappings during a rewrite if
* necessary. If we detect that we don't need to log anything we'll prevent
* any further action by the various logical rewrite functions.
*/
static void
logical_begin_heap_rewrite(RewriteState state)
{
HASHCTL hash_ctl;
TransactionId logical_xmin;
/*
* We only need to persist these mappings if the rewritten table can be
* accessed during logical decoding, if not, we can skip doing any
* additional work.
*/
state->rs_logical_rewrite =
RelationIsAccessibleInLogicalDecoding(state->rs_old_rel);
if (!state->rs_logical_rewrite)
return;
ProcArrayGetReplicationSlotXmin(NULL, &logical_xmin);
/*
* If there are no logical slots in progress we don't need to do anything,
* there cannot be any remappings for relevant rows yet. The relation's
* lock protects us against races.
*/
if (logical_xmin == InvalidTransactionId)
{
state->rs_logical_rewrite = false;
return;
}
state->rs_logical_xmin = logical_xmin;
state->rs_begin_lsn = GetXLogInsertRecPtr();
state->rs_num_rewrite_mappings = 0;
memset(&hash_ctl, 0, sizeof(hash_ctl));
hash_ctl.keysize = sizeof(TransactionId);
hash_ctl.entrysize = sizeof(RewriteMappingFile);
hash_ctl.hcxt = state->rs_cxt;
state->rs_logical_mappings =
hash_create("Logical rewrite mapping",
128, /* arbitrary initial size */
&hash_ctl,
HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
}
/*
* Flush all logical in-memory mappings to disk, but don't fsync them yet.
*/
static void
logical_heap_rewrite_flush_mappings(RewriteState state)
{
HASH_SEQ_STATUS seq_status;
RewriteMappingFile *src;
dlist_mutable_iter iter;
Assert(state->rs_logical_rewrite);
/* no logical rewrite in progress, no need to iterate over mappings */
if (state->rs_num_rewrite_mappings == 0)
return;
elog(DEBUG1, "flushing %u logical rewrite mapping entries",
state->rs_num_rewrite_mappings);
hash_seq_init(&seq_status, state->rs_logical_mappings);
while ((src = (RewriteMappingFile *) hash_seq_search(&seq_status)) != NULL)
{
char *waldata;
char *waldata_start;
xl_heap_rewrite_mapping xlrec;
Oid dboid;
uint32 len;
int written;
/* this file hasn't got any new mappings */
if (src->num_mappings == 0)
continue;
if (state->rs_old_rel->rd_rel->relisshared)
dboid = InvalidOid;
else
dboid = MyDatabaseId;
xlrec.num_mappings = src->num_mappings;
xlrec.mapped_rel = RelationGetRelid(state->rs_old_rel);
xlrec.mapped_xid = src->xid;
xlrec.mapped_db = dboid;
xlrec.offset = src->off;
xlrec.start_lsn = state->rs_begin_lsn;
/* write all mappings consecutively */
len = src->num_mappings * sizeof(LogicalRewriteMappingData);
waldata_start = waldata = palloc(len);
/*
* collect data we need to write out, but don't modify ondisk data yet
*/
dlist_foreach_modify(iter, &src->mappings)
{
RewriteMappingDataEntry *pmap;
pmap = dlist_container(RewriteMappingDataEntry, node, iter.cur);
memcpy(waldata, &pmap->map, sizeof(pmap->map));
waldata += sizeof(pmap->map);
/* remove from the list and free */
dlist_delete(&pmap->node);
pfree(pmap);
/* update bookkeeping */
state->rs_num_rewrite_mappings--;
src->num_mappings--;
}
Assert(src->num_mappings == 0);
Assert(waldata == waldata_start + len);
/*
* Note that we deviate from the usual WAL coding practices here,
* check the above "Logical rewrite support" comment for reasoning.
*/
written = FileWrite(src->vfd, waldata_start, len, src->off,
WAIT_EVENT_LOGICAL_REWRITE_WRITE);
if (written != len)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to file \"%s\", wrote %d of %d: %m", src->path,
written, len)));
src->off += len;
XLogBeginInsert();
XLogRegisterData((char *) (&xlrec), sizeof(xlrec));
XLogRegisterData(waldata_start, len);
/* write xlog record */
XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_REWRITE);
pfree(waldata_start);
}
Assert(state->rs_num_rewrite_mappings == 0);
}
/*
* Logical remapping part of end_heap_rewrite().
*/
static void
logical_end_heap_rewrite(RewriteState state)
{
HASH_SEQ_STATUS seq_status;
RewriteMappingFile *src;
/* done, no logical rewrite in progress */
if (!state->rs_logical_rewrite)
return;
/* writeout remaining in-memory entries */
if (state->rs_num_rewrite_mappings > 0)
logical_heap_rewrite_flush_mappings(state);
/* Iterate over all mappings we have written and fsync the files. */
hash_seq_init(&seq_status, state->rs_logical_mappings);
while ((src = (RewriteMappingFile *) hash_seq_search(&seq_status)) != NULL)
{
if (FileSync(src->vfd, WAIT_EVENT_LOGICAL_REWRITE_SYNC) != 0)
ereport(data_sync_elevel(ERROR),
(errcode_for_file_access(),
errmsg("could not fsync file \"%s\": %m", src->path)));
FileClose(src->vfd);
}
/* memory context cleanup will deal with the rest */
}
/*
* Log a single (old->new) mapping for 'xid'.
*/
static void
logical_rewrite_log_mapping(RewriteState state, TransactionId xid,
LogicalRewriteMappingData *map)
{
RewriteMappingFile *src;
RewriteMappingDataEntry *pmap;
Oid relid;
bool found;
relid = RelationGetRelid(state->rs_old_rel);
/* look for existing mappings for this 'mapped' xid */
src = hash_search(state->rs_logical_mappings, &xid,
HASH_ENTER, &found);
/*
* We haven't yet had the need to map anything for this xid, create
* per-xid data structures.
*/
if (!found)
{
char path[MAXPGPATH];
Oid dboid;
if (state->rs_old_rel->rd_rel->relisshared)
dboid = InvalidOid;
else
dboid = MyDatabaseId;
snprintf(path, MAXPGPATH,
"pg_logical/mappings/" LOGICAL_REWRITE_FORMAT,
dboid, relid,
(uint32) (state->rs_begin_lsn >> 32),
(uint32) state->rs_begin_lsn,
xid, GetCurrentTransactionId());
dlist_init(&src->mappings);
src->num_mappings = 0;
src->off = 0;
memcpy(src->path, path, sizeof(path));
src->vfd = PathNameOpenFile(path,
O_CREAT | O_EXCL | O_WRONLY | PG_BINARY);
if (src->vfd < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not create file \"%s\": %m", path)));
}
pmap = MemoryContextAlloc(state->rs_cxt,
sizeof(RewriteMappingDataEntry));
memcpy(&pmap->map, map, sizeof(LogicalRewriteMappingData));
dlist_push_tail(&src->mappings, &pmap->node);
src->num_mappings++;
state->rs_num_rewrite_mappings++;
/*
* Write out buffer every time we've too many in-memory entries across all
* mapping files.
*/
if (state->rs_num_rewrite_mappings >= 1000 /* arbitrary number */ )
logical_heap_rewrite_flush_mappings(state);
}
/*
* Perform logical remapping for a tuple that's mapped from old_tid to
* new_tuple->t_self by rewrite_heap_tuple() if necessary for the tuple.
*/
static void
logical_rewrite_heap_tuple(RewriteState state, ItemPointerData old_tid,
HeapTuple new_tuple)
{
ItemPointerData new_tid = new_tuple->t_self;
TransactionId cutoff = state->rs_logical_xmin;
TransactionId xmin;
TransactionId xmax;
bool do_log_xmin = false;
bool do_log_xmax = false;
LogicalRewriteMappingData map;
/* no logical rewrite in progress, we don't need to log anything */
if (!state->rs_logical_rewrite)
return;
xmin = HeapTupleHeaderGetXmin(new_tuple->t_data);
/* use *GetUpdateXid to correctly deal with multixacts */
xmax = HeapTupleHeaderGetUpdateXid(new_tuple->t_data);
/*
* Log the mapping iff the tuple has been created recently.
*/
if (TransactionIdIsNormal(xmin) && !TransactionIdPrecedes(xmin, cutoff))
do_log_xmin = true;
if (!TransactionIdIsNormal(xmax))
{
/*
* no xmax is set, can't have any permanent ones, so this check is
* sufficient
*/
}
else if (HEAP_XMAX_IS_LOCKED_ONLY(new_tuple->t_data->t_infomask))
{
/* only locked, we don't care */
}
else if (!TransactionIdPrecedes(xmax, cutoff))
{
/* tuple has been deleted recently, log */
do_log_xmax = true;
}
/* if neither needs to be logged, we're done */
if (!do_log_xmin && !do_log_xmax)
return;
/* fill out mapping information */
map.old_node = state->rs_old_rel->rd_node;
map.old_tid = old_tid;
map.new_node = state->rs_new_rel->rd_node;
map.new_tid = new_tid;
/* ---
* Now persist the mapping for the individual xids that are affected. We
* need to log for both xmin and xmax if they aren't the same transaction
* since the mapping files are per "affected" xid.
* We don't muster all that much effort detecting whether xmin and xmax
* are actually the same transaction, we just check whether the xid is the
* same disregarding subtransactions. Logging too much is relatively
* harmless and we could never do the check fully since subtransaction
* data is thrown away during restarts.
* ---
*/
if (do_log_xmin)
logical_rewrite_log_mapping(state, xmin, &map);
/* separately log mapping for xmax unless it'd be redundant */
if (do_log_xmax && !TransactionIdEquals(xmin, xmax))
logical_rewrite_log_mapping(state, xmax, &map);
}
/*
* Replay XLOG_HEAP2_REWRITE records
*/
void
heap_xlog_logical_rewrite(XLogReaderState *r)
{
char path[MAXPGPATH];
int fd;
xl_heap_rewrite_mapping *xlrec;
uint32 len;
char *data;
xlrec = (xl_heap_rewrite_mapping *) XLogRecGetData(r);
snprintf(path, MAXPGPATH,
"pg_logical/mappings/" LOGICAL_REWRITE_FORMAT,
xlrec->mapped_db, xlrec->mapped_rel,
(uint32) (xlrec->start_lsn >> 32),
(uint32) xlrec->start_lsn,
xlrec->mapped_xid, XLogRecGetXid(r));
fd = OpenTransientFile(path,
O_CREAT | O_WRONLY | PG_BINARY);
if (fd < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not create file \"%s\": %m", path)));
/*
* Truncate all data that's not guaranteed to have been safely fsynced (by
* previous record or by the last checkpoint).
*/
pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_TRUNCATE);
if (ftruncate(fd, xlrec->offset) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not truncate file \"%s\" to %u: %m",
path, (uint32) xlrec->offset)));
pgstat_report_wait_end();
/* now seek to the position we want to write our data to */
if (lseek(fd, xlrec->offset, SEEK_SET) != xlrec->offset)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek to end of file \"%s\": %m",
path)));
data = XLogRecGetData(r) + sizeof(*xlrec);
len = xlrec->num_mappings * sizeof(LogicalRewriteMappingData);
/* write out tail end of mapping file (again) */
errno = 0;
pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_MAPPING_WRITE);
if (write(fd, data, len) != len)
{
/* if write didn't set errno, assume problem is no disk space */
if (errno == 0)
errno = ENOSPC;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to file \"%s\": %m", path)));
}
pgstat_report_wait_end();
/*
* Now fsync all previously written data. We could improve things and only
* do this for the last write to a file, but the required bookkeeping
* doesn't seem worth the trouble.
*/
pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_MAPPING_SYNC);
if (pg_fsync(fd) != 0)
ereport(data_sync_elevel(ERROR),
(errcode_for_file_access(),
errmsg("could not fsync file \"%s\": %m", path)));
pgstat_report_wait_end();
if (CloseTransientFile(fd))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not close file \"%s\": %m", path)));
}
/* ---
* Perform a checkpoint for logical rewrite mappings
*
* This serves two tasks:
* 1) Remove all mappings not needed anymore based on the logical restart LSN
* 2) Flush all remaining mappings to disk, so that replay after a checkpoint
* only has to deal with the parts of a mapping that have been written out
* after the checkpoint started.
* ---
*/
void
CheckPointLogicalRewriteHeap(void)
{
XLogRecPtr cutoff;
XLogRecPtr redo;
DIR *mappings_dir;
struct dirent *mapping_de;
char path[MAXPGPATH + 20];
/*
* We start of with a minimum of the last redo pointer. No new decoding
* slot will start before that, so that's a safe upper bound for removal.
*/
redo = GetRedoRecPtr();
/* now check for the restart ptrs from existing slots */
cutoff = ReplicationSlotsComputeLogicalRestartLSN();
/* don't start earlier than the restart lsn */
if (cutoff != InvalidXLogRecPtr && redo < cutoff)
cutoff = redo;
mappings_dir = AllocateDir("pg_logical/mappings");
while ((mapping_de = ReadDir(mappings_dir, "pg_logical/mappings")) != NULL)
{
struct stat statbuf;
Oid dboid;
Oid relid;
XLogRecPtr lsn;
TransactionId rewrite_xid;
TransactionId create_xid;
uint32 hi,
lo;
if (strcmp(mapping_de->d_name, ".") == 0 ||
strcmp(mapping_de->d_name, "..") == 0)
continue;
snprintf(path, sizeof(path), "pg_logical/mappings/%s", mapping_de->d_name);
if (lstat(path, &statbuf) == 0 && !S_ISREG(statbuf.st_mode))
continue;
/* Skip over files that cannot be ours. */
if (strncmp(mapping_de->d_name, "map-", 4) != 0)
continue;
if (sscanf(mapping_de->d_name, LOGICAL_REWRITE_FORMAT,
&dboid, &relid, &hi, &lo, &rewrite_xid, &create_xid) != 6)
elog(ERROR, "could not parse filename \"%s\"", mapping_de->d_name);
lsn = ((uint64) hi) << 32 | lo;
if (lsn < cutoff || cutoff == InvalidXLogRecPtr)
{
elog(DEBUG1, "removing logical rewrite file \"%s\"", path);
if (unlink(path) < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not remove file \"%s\": %m", path)));
}
else
{
int fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
/*
* The file cannot vanish due to concurrency since this function
* is the only one removing logical mappings and it's run while
* CheckpointLock is held exclusively.
*/
if (fd < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open file \"%s\": %m", path)));
/*
* We could try to avoid fsyncing files that either haven't
* changed or have only been created since the checkpoint's start,
* but it's currently not deemed worth the effort.
*/
pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_CHECKPOINT_SYNC);
if (pg_fsync(fd) != 0)
ereport(data_sync_elevel(ERROR),
(errcode_for_file_access(),
errmsg("could not fsync file \"%s\": %m", path)));
pgstat_report_wait_end();
if (CloseTransientFile(fd))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not close file \"%s\": %m", path)));
}
}
FreeDir(mappings_dir);
}
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