greenplumn sharedtuplestore 源码
greenplumn sharedtuplestore 代码
文件路径:/src/backend/utils/sort/sharedtuplestore.c
/*-------------------------------------------------------------------------
*
* sharedtuplestore.c
* Simple mechanism for sharing tuples between backends.
*
* This module contains a shared temporary tuple storage mechanism providing
* a parallel-aware subset of the features of tuplestore.c. Multiple backends
* can write to a SharedTuplestore, and then multiple backends can later scan
* the stored tuples. Currently, the only scan type supported is a parallel
* scan where each backend reads an arbitrary subset of the tuples that were
* written.
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/utils/sort/sharedtuplestore.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup.h"
#include "access/htup_details.h"
#include "miscadmin.h"
#include "storage/buffile.h"
#include "storage/lwlock.h"
#include "storage/sharedfileset.h"
#include "utils/sharedtuplestore.h"
#include <limits.h>
/*
* The size of chunks, in pages. This is somewhat arbitrarily set to match
* the size of HASH_CHUNK, so that Parallel Hash obtains new chunks of tuples
* at approximately the same rate as it allocates new chunks of memory to
* insert them into.
*/
#define STS_CHUNK_PAGES 4
#define STS_CHUNK_HEADER_SIZE offsetof(SharedTuplestoreChunk, data)
#define STS_CHUNK_DATA_SIZE (STS_CHUNK_PAGES * BLCKSZ - STS_CHUNK_HEADER_SIZE)
/* Chunk written to disk. */
typedef struct SharedTuplestoreChunk
{
int ntuples; /* Number of tuples in this chunk. */
int overflow; /* If overflow, how many including this one? */
char data[FLEXIBLE_ARRAY_MEMBER];
} SharedTuplestoreChunk;
/* Per-participant shared state. */
typedef struct SharedTuplestoreParticipant
{
LWLock lock;
BlockNumber read_page; /* Page number for next read. */
BlockNumber npages; /* Number of pages written. */
bool writing; /* Used only for assertions. */
} SharedTuplestoreParticipant;
/* The control object that lives in shared memory. */
struct SharedTuplestore
{
int nparticipants; /* Number of participants that can write. */
int flags; /* Flag bits from SHARED_TUPLESTORE_XXX */
size_t meta_data_size; /* Size of per-tuple header. */
char name[NAMEDATALEN]; /* A name for this tuplestore. */
/* Followed by per-participant shared state. */
SharedTuplestoreParticipant participants[FLEXIBLE_ARRAY_MEMBER];
};
/* Per-participant state that lives in backend-local memory. */
struct SharedTuplestoreAccessor
{
int participant; /* My participant number. */
SharedTuplestore *sts; /* The shared state. */
SharedFileSet *fileset; /* The SharedFileSet holding files. */
MemoryContext context; /* Memory context for buffers. */
/* State for reading. */
int read_participant; /* The current participant to read from. */
BufFile *read_file; /* The current file to read from. */
int read_ntuples_available; /* The number of tuples in chunk. */
int read_ntuples; /* How many tuples have we read from chunk? */
size_t read_bytes; /* How many bytes have we read from chunk? */
char *read_buffer; /* A buffer for loading tuples. */
size_t read_buffer_size;
BlockNumber read_next_page; /* Lowest block we'll consider reading. */
/* State for writing. */
SharedTuplestoreChunk *write_chunk; /* Buffer for writing. */
BufFile *write_file; /* The current file to write to. */
BlockNumber write_page; /* The next page to write to. */
char *write_pointer; /* Current write pointer within chunk. */
char *write_end; /* One past the end of the current chunk. */
};
static void sts_filename(char *name, SharedTuplestoreAccessor *accessor,
int participant);
/*
* Return the amount of shared memory required to hold SharedTuplestore for a
* given number of participants.
*/
size_t
sts_estimate(int participants)
{
return offsetof(SharedTuplestore, participants) +
sizeof(SharedTuplestoreParticipant) * participants;
}
/*
* Initialize a SharedTuplestore in existing shared memory. There must be
* space for sts_estimate(participants) bytes. If flags includes the value
* SHARED_TUPLESTORE_SINGLE_PASS, the files may in future be removed more
* eagerly (but this isn't yet implemented).
*
* Tuples that are stored may optionally carry a piece of fixed sized
* meta-data which will be retrieved along with the tuple. This is useful for
* the hash values used in multi-batch hash joins, but could have other
* applications.
*
* The caller must supply a SharedFileSet, which is essentially a directory
* that will be cleaned up automatically, and a name which must be unique
* across all SharedTuplestores created in the same SharedFileSet.
*/
SharedTuplestoreAccessor *
sts_initialize(SharedTuplestore *sts, int participants,
int my_participant_number,
size_t meta_data_size,
int flags,
SharedFileSet *fileset,
const char *name)
{
SharedTuplestoreAccessor *accessor;
int i;
Assert(my_participant_number < participants);
sts->nparticipants = participants;
sts->meta_data_size = meta_data_size;
sts->flags = flags;
if (strlen(name) > sizeof(sts->name) - 1)
elog(ERROR, "SharedTuplestore name too long");
strcpy(sts->name, name);
/*
* Limit meta-data so it + tuple size always fits into a single chunk.
* sts_puttuple() and sts_read_tuple() could be made to support scenarios
* where that's not the case, but it's not currently required. If so,
* meta-data size probably should be made variable, too.
*/
if (meta_data_size + sizeof(uint32) >= STS_CHUNK_DATA_SIZE)
elog(ERROR, "meta-data too long");
for (i = 0; i < participants; ++i)
{
LWLockInitialize(&sts->participants[i].lock,
LWTRANCHE_SHARED_TUPLESTORE);
sts->participants[i].read_page = 0;
sts->participants[i].writing = false;
}
accessor = palloc0(sizeof(SharedTuplestoreAccessor));
accessor->participant = my_participant_number;
accessor->sts = sts;
accessor->fileset = fileset;
accessor->context = CurrentMemoryContext;
return accessor;
}
/*
* Attach to a SharedTuplestore that has been initialized by another backend,
* so that this backend can read and write tuples.
*/
SharedTuplestoreAccessor *
sts_attach(SharedTuplestore *sts,
int my_participant_number,
SharedFileSet *fileset)
{
SharedTuplestoreAccessor *accessor;
Assert(my_participant_number < sts->nparticipants);
accessor = palloc0(sizeof(SharedTuplestoreAccessor));
accessor->participant = my_participant_number;
accessor->sts = sts;
accessor->fileset = fileset;
accessor->context = CurrentMemoryContext;
return accessor;
}
static void
sts_flush_chunk(SharedTuplestoreAccessor *accessor)
{
size_t size;
size_t written;
size = STS_CHUNK_PAGES * BLCKSZ;
written = BufFileWrite(accessor->write_file, accessor->write_chunk, size);
if (written != size)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to temporary file: %m")));
memset(accessor->write_chunk, 0, size);
accessor->write_pointer = &accessor->write_chunk->data[0];
accessor->sts->participants[accessor->participant].npages +=
STS_CHUNK_PAGES;
}
/*
* Finish writing tuples. This must be called by all backends that have
* written data before any backend begins reading it.
*/
void
sts_end_write(SharedTuplestoreAccessor *accessor)
{
if (accessor->write_file != NULL)
{
sts_flush_chunk(accessor);
BufFileClose(accessor->write_file);
pfree(accessor->write_chunk);
accessor->write_chunk = NULL;
accessor->write_file = NULL;
accessor->sts->participants[accessor->participant].writing = false;
}
}
/*
* Prepare to rescan. Only one participant must call this. After it returns,
* all participants may call sts_begin_parallel_scan() and then loop over
* sts_parallel_scan_next(). This function must not be called concurrently
* with a scan, and synchronization to avoid that is the caller's
* responsibility.
*/
void
sts_reinitialize(SharedTuplestoreAccessor *accessor)
{
int i;
/*
* Reset the shared read head for all participants' files. Also set the
* initial chunk size to the minimum (any increases from that size will be
* recorded in chunk_expansion_log).
*/
for (i = 0; i < accessor->sts->nparticipants; ++i)
{
accessor->sts->participants[i].read_page = 0;
}
}
/*
* Begin scanning the contents in parallel.
*/
void
sts_begin_parallel_scan(SharedTuplestoreAccessor *accessor)
{
int i PG_USED_FOR_ASSERTS_ONLY;
/* End any existing scan that was in progress. */
sts_end_parallel_scan(accessor);
/*
* Any backend that might have written into this shared tuplestore must
* have called sts_end_write(), so that all buffers are flushed and the
* files have stopped growing.
*/
for (i = 0; i < accessor->sts->nparticipants; ++i)
Assert(!accessor->sts->participants[i].writing);
/*
* We will start out reading the file that THIS backend wrote. There may
* be some caching locality advantage to that.
*/
accessor->read_participant = accessor->participant;
accessor->read_file = NULL;
accessor->read_next_page = 0;
}
/*
* Finish a parallel scan, freeing associated backend-local resources.
*/
void
sts_end_parallel_scan(SharedTuplestoreAccessor *accessor)
{
/*
* Here we could delete all files if SHARED_TUPLESTORE_SINGLE_PASS, but
* we'd probably need a reference count of current parallel scanners so we
* could safely do it only when the reference count reaches zero.
*/
if (accessor->read_file != NULL)
{
BufFileClose(accessor->read_file);
accessor->read_file = NULL;
}
}
/*
* Write a tuple. If a meta-data size was provided to sts_initialize, then a
* pointer to meta data of that size must be provided.
*/
void
sts_puttuple(SharedTuplestoreAccessor *accessor, void *meta_data,
MinimalTuple tuple)
{
size_t size;
/* Do we have our own file yet? */
if (accessor->write_file == NULL)
{
SharedTuplestoreParticipant *participant;
char name[MAXPGPATH];
workfile_set *work_set;
/* Create one. Only this backend will write into it. */
sts_filename(name, accessor, accessor->participant);
work_set = workfile_mgr_create_set("SharedTupleStore", name, false /* hold pin */);
accessor->write_file = BufFileCreateShared(accessor->fileset, name, work_set);
/* Set up the shared state for this backend's file. */
participant = &accessor->sts->participants[accessor->participant];
participant->writing = true; /* for assertions only */
}
/* Do we have space? */
size = accessor->sts->meta_data_size + tuple->t_len;
if (accessor->write_pointer + size >= accessor->write_end)
{
if (accessor->write_chunk == NULL)
{
/* First time through. Allocate chunk. */
accessor->write_chunk = (SharedTuplestoreChunk *)
MemoryContextAllocZero(accessor->context,
STS_CHUNK_PAGES * BLCKSZ);
accessor->write_chunk->ntuples = 0;
accessor->write_pointer = &accessor->write_chunk->data[0];
accessor->write_end = (char *)
accessor->write_chunk + STS_CHUNK_PAGES * BLCKSZ;
}
else
{
/* See if flushing helps. */
sts_flush_chunk(accessor);
}
/* It may still not be enough in the case of a gigantic tuple. */
if (accessor->write_pointer + size >= accessor->write_end)
{
size_t written;
/*
* We'll write the beginning of the oversized tuple, and then
* write the rest in some number of 'overflow' chunks.
*
* sts_initialize() verifies that the size of the tuple +
* meta-data always fits into a chunk. Because the chunk has been
* flushed above, we can be sure to have all of a chunk's usable
* space available.
*/
Assert(accessor->write_pointer + accessor->sts->meta_data_size +
sizeof(uint32) < accessor->write_end);
/* Write the meta-data as one chunk. */
if (accessor->sts->meta_data_size > 0)
memcpy(accessor->write_pointer, meta_data,
accessor->sts->meta_data_size);
/*
* Write as much of the tuple as we can fit. This includes the
* tuple's size at the start.
*/
written = accessor->write_end - accessor->write_pointer -
accessor->sts->meta_data_size;
memcpy(accessor->write_pointer + accessor->sts->meta_data_size,
tuple, written);
++accessor->write_chunk->ntuples;
size -= accessor->sts->meta_data_size;
size -= written;
/* Now write as many overflow chunks as we need for the rest. */
while (size > 0)
{
size_t written_this_chunk;
sts_flush_chunk(accessor);
/*
* How many overflow chunks to go? This will allow readers to
* skip all of them at once instead of reading each one.
*/
accessor->write_chunk->overflow = (size + STS_CHUNK_DATA_SIZE - 1) /
STS_CHUNK_DATA_SIZE;
written_this_chunk =
Min(accessor->write_end - accessor->write_pointer, size);
memcpy(accessor->write_pointer, (char *) tuple + written,
written_this_chunk);
accessor->write_pointer += written_this_chunk;
size -= written_this_chunk;
written += written_this_chunk;
}
return;
}
}
/* Copy meta-data and tuple into buffer. */
if (accessor->sts->meta_data_size > 0)
memcpy(accessor->write_pointer, meta_data,
accessor->sts->meta_data_size);
memcpy(accessor->write_pointer + accessor->sts->meta_data_size, tuple,
tuple->t_len);
accessor->write_pointer += size;
++accessor->write_chunk->ntuples;
}
static MinimalTuple
sts_read_tuple(SharedTuplestoreAccessor *accessor, void *meta_data)
{
MinimalTuple tuple;
uint32 size;
size_t remaining_size;
size_t this_chunk_size;
char *destination;
/*
* We'll keep track of bytes read from this chunk so that we can detect an
* overflowing tuple and switch to reading overflow pages.
*/
if (accessor->sts->meta_data_size > 0)
{
if (BufFileRead(accessor->read_file,
meta_data,
accessor->sts->meta_data_size) !=
accessor->sts->meta_data_size)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from shared tuplestore temporary file"),
errdetail_internal("Short read while reading meta-data.")));
accessor->read_bytes += accessor->sts->meta_data_size;
}
if (BufFileRead(accessor->read_file,
&size,
sizeof(size)) != sizeof(size))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from shared tuplestore temporary file"),
errdetail_internal("Short read while reading size.")));
accessor->read_bytes += sizeof(size);
if (size > accessor->read_buffer_size)
{
size_t new_read_buffer_size;
if (accessor->read_buffer != NULL)
pfree(accessor->read_buffer);
new_read_buffer_size = Max(size, accessor->read_buffer_size * 2);
accessor->read_buffer =
MemoryContextAlloc(accessor->context, new_read_buffer_size);
accessor->read_buffer_size = new_read_buffer_size;
}
remaining_size = size - sizeof(uint32);
this_chunk_size = Min(remaining_size,
BLCKSZ * STS_CHUNK_PAGES - accessor->read_bytes);
destination = accessor->read_buffer + sizeof(uint32);
if (BufFileRead(accessor->read_file,
destination,
this_chunk_size) != this_chunk_size)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from shared tuplestore temporary file"),
errdetail_internal("Short read while reading tuple.")));
accessor->read_bytes += this_chunk_size;
remaining_size -= this_chunk_size;
destination += this_chunk_size;
++accessor->read_ntuples;
/* Check if we need to read any overflow chunks. */
while (remaining_size > 0)
{
/* We are now positioned at the start of an overflow chunk. */
SharedTuplestoreChunk chunk_header;
if (BufFileRead(accessor->read_file, &chunk_header, STS_CHUNK_HEADER_SIZE) !=
STS_CHUNK_HEADER_SIZE)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from shared tuplestore temporary file"),
errdetail_internal("Short read while reading overflow chunk header.")));
accessor->read_bytes = STS_CHUNK_HEADER_SIZE;
if (chunk_header.overflow == 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("unexpected chunk in shared tuplestore temporary file"),
errdetail_internal("Expected overflow chunk.")));
accessor->read_next_page += STS_CHUNK_PAGES;
this_chunk_size = Min(remaining_size,
BLCKSZ * STS_CHUNK_PAGES -
STS_CHUNK_HEADER_SIZE);
if (BufFileRead(accessor->read_file,
destination,
this_chunk_size) != this_chunk_size)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from shared tuplestore temporary file"),
errdetail_internal("Short read while reading tuple.")));
accessor->read_bytes += this_chunk_size;
remaining_size -= this_chunk_size;
destination += this_chunk_size;
/*
* These will be used to count regular tuples following the oversized
* tuple that spilled into this overflow chunk.
*/
accessor->read_ntuples = 0;
accessor->read_ntuples_available = chunk_header.ntuples;
}
tuple = (MinimalTuple) accessor->read_buffer;
tuple->t_len = size;
return tuple;
}
/*
* Get the next tuple in the current parallel scan.
*/
MinimalTuple
sts_parallel_scan_next(SharedTuplestoreAccessor *accessor, void *meta_data)
{
SharedTuplestoreParticipant *p;
BlockNumber read_page;
bool eof;
for (;;)
{
/* Can we read more tuples from the current chunk? */
if (accessor->read_ntuples < accessor->read_ntuples_available)
return sts_read_tuple(accessor, meta_data);
/* Find the location of a new chunk to read. */
p = &accessor->sts->participants[accessor->read_participant];
LWLockAcquire(&p->lock, LW_EXCLUSIVE);
/* We can skip directly past overflow pages we know about. */
if (p->read_page < accessor->read_next_page)
p->read_page = accessor->read_next_page;
eof = p->read_page >= p->npages;
if (!eof)
{
/* Claim the next chunk. */
read_page = p->read_page;
/* Advance the read head for the next reader. */
p->read_page += STS_CHUNK_PAGES;
accessor->read_next_page = p->read_page;
}
LWLockRelease(&p->lock);
if (!eof)
{
SharedTuplestoreChunk chunk_header;
/* Make sure we have the file open. */
if (accessor->read_file == NULL)
{
char name[MAXPGPATH];
sts_filename(name, accessor, accessor->read_participant);
accessor->read_file =
BufFileOpenShared(accessor->fileset, name);
}
/* Seek and load the chunk header. */
if (BufFileSeekBlock(accessor->read_file, read_page) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from shared tuplestore temporary file"),
errdetail_internal("Could not seek to next block.")));
if (BufFileRead(accessor->read_file, &chunk_header,
STS_CHUNK_HEADER_SIZE) != STS_CHUNK_HEADER_SIZE)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from shared tuplestore temporary file"),
errdetail_internal("Short read while reading chunk header.")));
/*
* If this is an overflow chunk, we skip it and any following
* overflow chunks all at once.
*/
if (chunk_header.overflow > 0)
{
accessor->read_next_page = read_page +
chunk_header.overflow * STS_CHUNK_PAGES;
continue;
}
accessor->read_ntuples = 0;
accessor->read_ntuples_available = chunk_header.ntuples;
accessor->read_bytes = STS_CHUNK_HEADER_SIZE;
/* Go around again, so we can get a tuple from this chunk. */
}
else
{
if (accessor->read_file != NULL)
{
BufFileClose(accessor->read_file);
accessor->read_file = NULL;
}
/*
* Try the next participant's file. If we've gone full circle,
* we're done.
*/
accessor->read_participant = (accessor->read_participant + 1) %
accessor->sts->nparticipants;
if (accessor->read_participant == accessor->participant)
break;
accessor->read_next_page = 0;
/* Go around again, so we can get a chunk from this file. */
}
}
return NULL;
}
/*
* Create the name used for the BufFile that a given participant will write.
*/
static void
sts_filename(char *name, SharedTuplestoreAccessor *accessor, int participant)
{
snprintf(name, MAXPGPATH, "%s.p%d", accessor->sts->name, participant);
}
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