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Add support for LZ4 with compression of full-page writes in WAL

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The logic is implemented so as there can be a choice in the compression
used when building a WAL record, and an extra per-record bit is used to
track down if a block is compressed with PGLZ, LZ4 or nothing.

wal_compression, the existing parameter, is changed to an enum with
support for the following backward-compatible values:
- "off", the default, to not use compression.
- "pglz" or "on", to compress FPWs with PGLZ.
- "lz4", the new mode, to compress FPWs with LZ4.

Benchmarking has showed that LZ4 outclasses easily PGLZ.  ZSTD would be
also an interesting choice, but going just with LZ4 for now makes the
patch minimalistic as toast compression is already able to use LZ4, so
there is no need to worry about any build-related needs for this
implementation.

Author: Andrey Borodin, Justin Pryzby
Reviewed-by: Dilip Kumar, Michael Paquier
Discussion: https://postgr.es/m/3037310D-ECB7-4BF1-AF20-01C10BB33A33@yandex-team.ru
This commit is contained in:
Michael Paquier
2021-06-29 11:17:55 +09:00
parent cc2c7d65fc
commit 4035cd5d4e
13 changed files with 191 additions and 52 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
src/backend/access/transam/xlog.c
View File

@ -98,7 +98,7 @@ char *XLogArchiveCommand = NULL;
bool EnableHotStandby = false;
bool fullPageWrites = true;
bool wal_log_hints = false;
bool wal_compression = false;
int wal_compression = WAL_COMPRESSION_NONE;
char *wal_consistency_checking_string = NULL;
bool *wal_consistency_checking = NULL;
bool wal_init_zero = true;

73
src/backend/access/transam/xloginsert.c
View File

@ -33,8 +33,20 @@
#include "storage/proc.h"
#include "utils/memutils.h"
/* Buffer size required to store a compressed version of backup block image */
#define PGLZ_MAX_BLCKSZ PGLZ_MAX_OUTPUT(BLCKSZ)
/*
* Guess the maximum buffer size required to store a compressed version of
* backup block image.
*/
#ifdef USE_LZ4
#include <lz4.h>
#define LZ4_MAX_BLCKSZ LZ4_COMPRESSBOUND(BLCKSZ)
#else
#define LZ4_MAX_BLCKSZ 0
#endif
#define PGLZ_MAX_BLCKSZ PGLZ_MAX_OUTPUT(BLCKSZ)
#define COMPRESS_BUFSIZE Max(PGLZ_MAX_BLCKSZ, LZ4_MAX_BLCKSZ)
/*
* For each block reference registered with XLogRegisterBuffer, we fill in
@ -58,7 +70,7 @@ typedef struct
* backup block data in XLogRecordAssemble() */
/* buffer to store a compressed version of backup block image */
char compressed_page[PGLZ_MAX_BLCKSZ];
char compressed_page[COMPRESS_BUFSIZE];
} registered_buffer;
static registered_buffer *registered_buffers;
@ -628,7 +640,7 @@ XLogRecordAssemble(RmgrId rmid, uint8 info,
/*
* Try to compress a block image if wal_compression is enabled
*/
if (wal_compression)
if (wal_compression != WAL_COMPRESSION_NONE)
{
is_compressed =
XLogCompressBackupBlock(page, bimg.hole_offset,
@ -665,8 +677,29 @@ XLogRecordAssemble(RmgrId rmid, uint8 info,
if (is_compressed)
{
/* The current compression is stored in the WAL record */
bimg.length = compressed_len;
bimg.bimg_info |= BKPIMAGE_IS_COMPRESSED;
/* Set the compression method used for this block */
switch ((WalCompression) wal_compression)
{
case WAL_COMPRESSION_PGLZ:
bimg.bimg_info |= BKPIMAGE_COMPRESS_PGLZ;
break;
case WAL_COMPRESSION_LZ4:
#ifdef USE_LZ4
bimg.bimg_info |= BKPIMAGE_COMPRESS_LZ4;
#else
elog(ERROR, "LZ4 is not supported by this build");
#endif
break;
case WAL_COMPRESSION_NONE:
Assert(false); /* cannot happen */
break;
/* no default case, so that compiler will warn */
}
rdt_datas_last->data = regbuf->compressed_page;
rdt_datas_last->len = compressed_len;
@ -853,12 +886,34 @@ XLogCompressBackupBlock(char *page, uint16 hole_offset, uint16 hole_length,
else
source = page;
switch ((WalCompression) wal_compression)
{
case WAL_COMPRESSION_PGLZ:
len = pglz_compress(source, orig_len, dest, PGLZ_strategy_default);
break;
case WAL_COMPRESSION_LZ4:
#ifdef USE_LZ4
len = LZ4_compress_default(source, dest, orig_len,
COMPRESS_BUFSIZE);
if (len <= 0)
len = -1; /* failure */
#else
elog(ERROR, "LZ4 is not supported by this build");
#endif
break;
case WAL_COMPRESSION_NONE:
Assert(false); /* cannot happen */
break;
/* no default case, so that compiler will warn */
}
/*
* We recheck the actual size even if pglz_compress() reports success and
* see if the number of bytes saved by compression is larger than the
* length of extra data needed for the compressed version of block image.
* We recheck the actual size even if compression reports success and see
* if the number of bytes saved by compression is larger than the length
* of extra data needed for the compressed version of block image.
*/
len = pglz_compress(source, orig_len, dest, PGLZ_strategy_default);
if (len >= 0 &&
len + extra_bytes < orig_len)
{

58
src/backend/access/transam/xlogreader.c
View File

@ -18,6 +18,9 @@
#include "postgres.h"
#include <unistd.h>
#ifdef USE_LZ4
#include <lz4.h>
#endif
#include "access/transam.h"
#include "access/xlog_internal.h"
@ -1290,7 +1293,7 @@ DecodeXLogRecord(XLogReaderState *state, XLogRecord *record, char **errormsg)
blk->apply_image = ((blk->bimg_info & BKPIMAGE_APPLY) != 0);
if (blk->bimg_info & BKPIMAGE_IS_COMPRESSED)
if (BKPIMAGE_COMPRESSED(blk->bimg_info))
{
if (blk->bimg_info & BKPIMAGE_HAS_HOLE)
COPY_HEADER_FIELD(&blk->hole_length, sizeof(uint16));
@ -1335,29 +1338,28 @@ DecodeXLogRecord(XLogReaderState *state, XLogRecord *record, char **errormsg)
}
/*
* cross-check that bimg_len < BLCKSZ if the IS_COMPRESSED
* flag is set.
* Cross-check that bimg_len < BLCKSZ if it is compressed.
*/
if ((blk->bimg_info & BKPIMAGE_IS_COMPRESSED) &&
if (BKPIMAGE_COMPRESSED(blk->bimg_info) &&
blk->bimg_len == BLCKSZ)
{
report_invalid_record(state,
"BKPIMAGE_IS_COMPRESSED set, but block image length %u at %X/%X",
"BKPIMAGE_COMPRESSED set, but block image length %u at %X/%X",
(unsigned int) blk->bimg_len,
LSN_FORMAT_ARGS(state->ReadRecPtr));
goto err;
}
/*
* cross-check that bimg_len = BLCKSZ if neither HAS_HOLE nor
* IS_COMPRESSED flag is set.
* cross-check that bimg_len = BLCKSZ if neither HAS_HOLE is
* set nor COMPRESSED().
*/
if (!(blk->bimg_info & BKPIMAGE_HAS_HOLE) &&
!(blk->bimg_info & BKPIMAGE_IS_COMPRESSED) &&
!BKPIMAGE_COMPRESSED(blk->bimg_info) &&
blk->bimg_len != BLCKSZ)
{
report_invalid_record(state,
"neither BKPIMAGE_HAS_HOLE nor BKPIMAGE_IS_COMPRESSED set, but block image length is %u at %X/%X",
"neither BKPIMAGE_HAS_HOLE nor BKPIMAGE_COMPRESSED set, but block image length is %u at %X/%X",
(unsigned int) blk->data_len,
LSN_FORMAT_ARGS(state->ReadRecPtr));
goto err;
@ -1555,17 +1557,49 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
bkpb = &record->blocks[block_id];
ptr = bkpb->bkp_image;
if (bkpb->bimg_info & BKPIMAGE_IS_COMPRESSED)
if (BKPIMAGE_COMPRESSED(bkpb->bimg_info))
{
/* If a backup block image is compressed, decompress it */
if (pglz_decompress(ptr, bkpb->bimg_len, tmp.data,
BLCKSZ - bkpb->hole_length, true) < 0)
bool decomp_success = true;
if ((bkpb->bimg_info & BKPIMAGE_COMPRESS_PGLZ) != 0)
{
if (pglz_decompress(ptr, bkpb->bimg_len, tmp.data,
BLCKSZ - bkpb->hole_length, true) < 0)
decomp_success = false;
}
else if ((bkpb->bimg_info & BKPIMAGE_COMPRESS_LZ4) != 0)
{
#ifdef USE_LZ4
if (LZ4_decompress_safe(ptr, tmp.data,
bkpb->bimg_len, BLCKSZ - bkpb->hole_length) <= 0)
decomp_success = false;
#else
report_invalid_record(record, "image at %X/%X compressed with %s not supported by build, block %d",
(uint32) (record->ReadRecPtr >> 32),
(uint32) record->ReadRecPtr,
"LZ4",
block_id);
return false;
#endif
}
else
{
report_invalid_record(record, "image at %X/%X compressed with unknown method, block %d",
(uint32) (record->ReadRecPtr >> 32),
(uint32) record->ReadRecPtr,
block_id);
return false;
}
if (!decomp_success)
{
report_invalid_record(record, "invalid compressed image at %X/%X, block %d",
LSN_FORMAT_ARGS(record->ReadRecPtr),
block_id);
return false;
}
ptr = tmp.data;
}

36
src/backend/utils/misc/guc.c
View File

@ -540,6 +540,22 @@ static struct config_enum_entry default_toast_compression_options[] = {
{NULL, 0, false}
};
static const struct config_enum_entry wal_compression_options[] = {
{"pglz", WAL_COMPRESSION_PGLZ, false},
#ifdef USE_LZ4
{"lz4", WAL_COMPRESSION_LZ4, false},
#endif
{"on", WAL_COMPRESSION_PGLZ, false},
{"off", WAL_COMPRESSION_NONE, false},
{"true", WAL_COMPRESSION_PGLZ, true},
{"false", WAL_COMPRESSION_NONE, true},
{"yes", WAL_COMPRESSION_PGLZ, true},
{"no", WAL_COMPRESSION_NONE, true},
{"1", WAL_COMPRESSION_PGLZ, true},
{"0", WAL_COMPRESSION_NONE, true},
{NULL, 0, false}
};
/*
* Options for enum values stored in other modules
*/
@ -1304,16 +1320,6 @@ static struct config_bool ConfigureNamesBool[] =
NULL, NULL, NULL
},
{
{"wal_compression", PGC_SUSET, WAL_SETTINGS,
gettext_noop("Compresses full-page writes written in WAL file."),
NULL
},
&wal_compression,
false,
NULL, NULL, NULL
},
{
{"wal_init_zero", PGC_SUSET, WAL_SETTINGS,
gettext_noop("Writes zeroes to new WAL files before first use."),
@ -4816,6 +4822,16 @@ static struct config_enum ConfigureNamesEnum[] =
NULL, NULL, NULL
},
{
{"wal_compression", PGC_SUSET, WAL_SETTINGS,
gettext_noop("Compresses full-page writes written in WAL file with specified method."),
NULL
},
&wal_compression,
WAL_COMPRESSION_NONE, wal_compression_options,
NULL, NULL, NULL
},
{
{"wal_level", PGC_POSTMASTER, WAL_SETTINGS,
gettext_noop("Sets the level of information written to the WAL."),

3
src/backend/utils/misc/postgresql.conf.sample
View File

@ -218,7 +218,8 @@
#full_page_writes = on # recover from partial page writes
#wal_log_hints = off # also do full page writes of non-critical updates
# (change requires restart)
#wal_compression = off # enable compression of full-page writes
#wal_compression = off # enables compression of full-page writes;
# off, pglz, lz4, or on
#wal_init_zero = on # zero-fill new WAL files
#wal_recycle = on # recycle WAL files
#wal_buffers = -1 # min 32kB, -1 sets based on shared_buffers