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

michaelpq · michaelpq · commit 4035cd5d4eee · 2021-06-29T11:17:55.000+09:00
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
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
@@ -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.
diff --git a/doc/src/sgml/install-windows.sgml b/doc/src/sgml/install-windows.sgml
@@ -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>
diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
@@ -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>
diff --git a/doc/src/sgml/standalone-profile.xsl b/doc/src/sgml/standalone-profile.xsl
@@ -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>
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -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;
diff --git a/src/backend/access/transam/xloginsert.c b/src/backend/access/transam/xloginsert.c
@@ -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)
 	{
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
@@ -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;
 	}
 
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
@@ -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."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
@@ -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
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
diff --git a/src/include/access/xlogrecord.h b/src/include/access/xlogrecord.h
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
