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

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
doc/src/sgml/config.sgml
View File

@ -3128,23 +3128,27 @@ include_dir 'conf.d'
</varlistentry>
<varlistentry id="guc-wal-compression" xreflabel="wal_compression">
<term><varname>wal_compression</varname> (<type>boolean</type>)
<term><varname>wal_compression</varname> (<type>enum</type>)
<indexterm>
<primary><varname>wal_compression</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
When this parameter is <literal>on</literal>, the <productname>PostgreSQL</productname>
This parameter enables compression of WAL using the specified
compression method.
When enabled, the <productname>PostgreSQL</productname>
server compresses full page images written to WAL when
<xref linkend="guc-full-page-writes"/> is on or during a base backup.
A compressed page image will be decompressed during WAL replay.
The default value is <literal>off</literal>.
Only superusers can change this setting.
The supported methods are <literal>pglz</literal> and
<literal>lz4</literal> (if <productname>PostgreSQL</productname> was
compiled with <option>--with-lz4</option>). The default value is
<literal>off</literal>. Only superusers can change this setting.
</para>
<para>
Turning this parameter on can reduce the WAL volume without
Enabling compression can reduce the WAL volume without
increasing the risk of unrecoverable data corruption,
but at the cost of some extra CPU spent on the compression during
WAL logging and on the decompression during WAL replay.

2
doc/src/sgml/install-windows.sgml
View File

@ -299,7 +299,7 @@ $ENV{MSBFLAGS}="/m";
<term><productname>LZ4</productname></term>
<listitem><para>
Required for supporting <productname>LZ4</productname> compression
method for compressing the table data. Binaries and source can be
method for compressing table or WAL data. Binaries and source can be
downloaded from
<ulink url="https://github.com/lz4/lz4/releases"></ulink>.
</para></listitem>

5
doc/src/sgml/installation.sgml
View File

@ -270,7 +270,8 @@ su - postgres
<para>
You need <productname>LZ4</productname>, if you want to support
compression of data with this method; see
<xref linkend="guc-default-toast-compression"/>.
<xref linkend="guc-default-toast-compression"/> and
<xref linkend="guc-wal-compression"/>.
</para>
</listitem>
@ -980,7 +981,7 @@ build-postgresql:
<para>
Build with <productname>LZ4</productname> compression support.
This allows the use of <productname>LZ4</productname> for
compression of table data.
compression of table and WAL data.
</para>
</listitem>
</varlistentry>

4
doc/src/sgml/standalone-profile.xsl
View File

@ -52,6 +52,10 @@ variant without links and references to the main documentation.
<xsl:text>the configuration parameter default_toast_compression</xsl:text>
</xsl:template>
<xsl:template match="xref[@linkend='guc-wal-compression']">
<xsl:text>the configuration parameter wal_compression</xsl:text>
</xsl:template>
<xsl:template match="xref[@linkend='install-windows']">
<xsl:text>the documentation</xsl:text>
</xsl:template>

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

19
src/bin/pg_waldump/pg_waldump.c
View File

@ -537,18 +537,29 @@ XLogDumpDisplayRecord(XLogDumpConfig *config, XLogReaderState *record)
blk);
if (XLogRecHasBlockImage(record, block_id))
{
if (record->blocks[block_id].bimg_info &
BKPIMAGE_IS_COMPRESSED)
uint8 bimg_info = record->blocks[block_id].bimg_info;
if (BKPIMAGE_COMPRESSED(bimg_info))
{
const char *method;
if ((bimg_info & BKPIMAGE_COMPRESS_PGLZ) != 0)
method = "pglz";
else if ((bimg_info & BKPIMAGE_COMPRESS_LZ4) != 0)
method = "lz4";
else
method = "unknown";
printf(" (FPW%s); hole: offset: %u, length: %u, "
"compression saved: %u",
"compression saved: %u, method: %s",
XLogRecBlockImageApply(record, block_id) ?
"" : " for WAL verification",
record->blocks[block_id].hole_offset,
record->blocks[block_id].hole_length,
BLCKSZ -
record->blocks[block_id].hole_length -
record->blocks[block_id].bimg_len);
record->blocks[block_id].bimg_len,
method);
}
else
{

10
src/include/access/xlog.h
View File

@ -116,7 +116,7 @@ extern char *XLogArchiveCommand;
extern bool EnableHotStandby;
extern bool fullPageWrites;
extern bool wal_log_hints;
extern bool wal_compression;
extern int wal_compression;
extern bool wal_init_zero;
extern bool wal_recycle;
extern bool *wal_consistency_checking;
@ -167,6 +167,14 @@ typedef enum WalLevel
WAL_LEVEL_LOGICAL
} WalLevel;
/* Compression algorithms for WAL */
typedef enum WalCompression
{
WAL_COMPRESSION_NONE = 0,
WAL_COMPRESSION_PGLZ,
WAL_COMPRESSION_LZ4
} WalCompression;
/* Recovery states */
typedef enum RecoveryState
{

16
src/include/access/xlogrecord.h
View File

@ -114,8 +114,8 @@ typedef struct XLogRecordBlockHeader
* present is (BLCKSZ - <length of "hole" bytes>).
*
* Additionally, when wal_compression is enabled, we will try to compress full
* page images using the PGLZ compression algorithm, after removing the "hole".
* This can reduce the WAL volume, but at some extra cost of CPU spent
* page images using one of the supported algorithms, after removing the
* "hole". This can reduce the WAL volume, but at some extra cost of CPU spent
* on the compression during WAL logging. In this case, since the "hole"
* length cannot be calculated by subtracting the number of page image bytes
* from BLCKSZ, basically it needs to be stored as an extra information.
@ -134,7 +134,7 @@ typedef struct XLogRecordBlockImageHeader
uint8 bimg_info; /* flag bits, see below */
/*
* If BKPIMAGE_HAS_HOLE and BKPIMAGE_IS_COMPRESSED, an
* If BKPIMAGE_HAS_HOLE and BKPIMAGE_COMPRESSED(), an
* XLogRecordBlockCompressHeader struct follows.
*/
} XLogRecordBlockImageHeader;
@ -144,9 +144,13 @@ typedef struct XLogRecordBlockImageHeader
/* Information stored in bimg_info */
#define BKPIMAGE_HAS_HOLE 0x01 /* page image has "hole" */
#define BKPIMAGE_IS_COMPRESSED 0x02 /* page image is compressed */
#define BKPIMAGE_APPLY 0x04 /* page image should be restored during
* replay */
#define BKPIMAGE_APPLY 0x02 /* page image should be restored
* during replay */
/* compression methods supported */
#define BKPIMAGE_COMPRESS_PGLZ 0x04
#define BKPIMAGE_COMPRESS_LZ4 0x08
#define BKPIMAGE_COMPRESSED(info) \
((info & (BKPIMAGE_COMPRESS_PGLZ | BKPIMAGE_COMPRESS_LZ4)) != 0)
/*
* Extra header information used when page image has "hole" and

1
src/tools/pgindent/typedefs.list
View File

@ -2843,6 +2843,7 @@ WaitEventSet
WaitEventTimeout
WaitPMResult
WalCloseMethod
WalCompression
WalLevel
WalRcvData
WalRcvExecResult