Subject: [PATCH v5 3/3] Change policy of XLog read-buffer allocation

From: Kyotaro Horiguchi <[email-masked]>
Date: Thu, 5 Sep 2019 21:29:32 +0900

Page buffer in XLogReaderState was allocated by XLogReaderAllcoate but
actually it'd be the responsibility to the callers of XLogReadRecord,
which now actually reads in pages. This patch does that.
---
 src/backend/access/transam/twophase.c     |  2 ++
 src/backend/access/transam/xlog.c         |  2 ++
 src/backend/access/transam/xlogreader.c   | 18 ------------------
 src/backend/replication/logical/logical.c |  2 ++
 src/bin/pg_rewind/parsexlog.c             |  6 ++++++
 src/bin/pg_waldump/pg_waldump.c           |  2 ++
 6 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 929da4eef2..9ec88b35ef 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1392,6 +1392,7 @@ XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
 				(errcode(ERRCODE_OUT_OF_MEMORY),
 				 errmsg("out of memory"),
 				 errdetail("Failed while allocating a WAL reading processor.")));
+	xlogreader->readBuf = palloc(XLOG_BLCKSZ);
 
 	while (XLogReadRecord(xlogreader, lsn, &record, &errormsg) ==
 		   XLREAD_NEED_DATA)
@@ -1421,6 +1422,7 @@ XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
 	*buf = palloc(sizeof(char) * XLogRecGetDataLen(xlogreader));
 	memcpy(*buf, XLogRecGetData(xlogreader), sizeof(char) * XLogRecGetDataLen(xlogreader));
 
+	pfree(xlogreader->readBuf);
 	XLogReaderFree(xlogreader);
 }
 
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 96e2115aad..425f7a12bd 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -6351,6 +6351,7 @@ StartupXLOG(void)
 				(errcode(ERRCODE_OUT_OF_MEMORY),
 				 errmsg("out of memory"),
 				 errdetail("Failed while allocating a WAL reading processor.")));
+	xlogreader->readBuf = palloc(XLOG_BLCKSZ);
 	xlogreader->system_identifier = ControlFile->system_identifier;
 
 	/*
@@ -7722,6 +7723,7 @@ StartupXLOG(void)
 		close(readFile);
 		readFile = -1;
 	}
+	pfree(xlogreader->readBuf);
 	XLogReaderFree(xlogreader);
 
 	/*
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 66bd9eb8d7..26f6834b8f 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -79,27 +79,11 @@ XLogReaderAllocate(int wal_segment_size)
 
 	state->max_block_id = -1;
 
-	/*
-	 * Permanently allocate readBuf.  We do it this way, rather than just
-	 * making a static array, for two reasons: (1) no need to waste the
-	 * storage in most instantiations of the backend; (2) a static char array
-	 * isn't guaranteed to have any particular alignment, whereas
-	 * palloc_extended() will provide MAXALIGN'd storage.
-	 */
-	state->readBuf = (char *) palloc_extended(XLOG_BLCKSZ,
-											  MCXT_ALLOC_NO_OOM);
-	if (!state->readBuf)
-	{
-		pfree(state);
-		return NULL;
-	}
-
 	state->wal_segment_size = wal_segment_size;
 	state->errormsg_buf = palloc_extended(MAX_ERRORMSG_LEN + 1,
 										  MCXT_ALLOC_NO_OOM);
 	if (!state->errormsg_buf)
 	{
-		pfree(state->readBuf);
 		pfree(state);
 		return NULL;
 	}
@@ -112,7 +96,6 @@ XLogReaderAllocate(int wal_segment_size)
 	if (!allocate_recordbuf(state, 0))
 	{
 		pfree(state->errormsg_buf);
-		pfree(state->readBuf);
 		pfree(state);
 		return NULL;
 	}
@@ -136,7 +119,6 @@ XLogReaderFree(XLogReaderState *state)
 	pfree(state->errormsg_buf);
 	if (state->readRecordBuf)
 		pfree(state->readRecordBuf);
-	pfree(state->readBuf);
 	pfree(state);
 }
 
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 11e52e4c01..ea027caa69 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -178,6 +178,7 @@ StartupDecodingContext(List *output_plugin_options,
 		ereport(ERROR,
 				(errcode(ERRCODE_OUT_OF_MEMORY),
 				 errmsg("out of memory")));
+	ctx->reader->readBuf = palloc(XLOG_BLCKSZ);
 	ctx->read_page = read_page;
 
 	ctx->reorder = ReorderBufferAllocate();
@@ -523,6 +524,7 @@ FreeDecodingContext(LogicalDecodingContext *ctx)
 
 	ReorderBufferFree(ctx->reorder);
 	FreeSnapshotBuilder(ctx->snapshot_builder);
+	pfree(ctx->reader->readBuf);
 	XLogReaderFree(ctx->reader);
 	MemoryContextDelete(ctx->context);
 }
diff --git a/src/bin/pg_rewind/parsexlog.c b/src/bin/pg_rewind/parsexlog.c
index ff26b30f82..c60267e87e 100644
--- a/src/bin/pg_rewind/parsexlog.c
+++ b/src/bin/pg_rewind/parsexlog.c
@@ -60,6 +60,7 @@ extractPageMap(const char *datadir, XLogRecPtr startpoint, int tliIndex,
 	xlogreader = XLogReaderAllocate(WalSegSz);
 	if (xlogreader == NULL)
 		pg_fatal("out of memory");
+	xlogreader->readBuf = pg_malloc(XLOG_BLCKSZ);
 
 	do
 	{
@@ -92,6 +93,7 @@ extractPageMap(const char *datadir, XLogRecPtr startpoint, int tliIndex,
 
 	} while (xlogreader->ReadRecPtr != endpoint);
 
+	pg_free(xlogreader->readBuf);
 	XLogReaderFree(xlogreader);
 	if (xlogreadfd != -1)
 	{
@@ -115,6 +117,7 @@ readOneRecord(const char *datadir, XLogRecPtr ptr, int tliIndex)
 	xlogreader = XLogReaderAllocate(WalSegSz);
 	if (xlogreader == NULL)
 		pg_fatal("out of memory");
+	xlogreader->readBuf = pg_malloc(XLOG_BLCKSZ);
 
 	while (XLogReadRecord(xlogreader, ptr, &record, &errormsg) ==
 		   XLREAD_NEED_DATA)
@@ -133,6 +136,7 @@ readOneRecord(const char *datadir, XLogRecPtr ptr, int tliIndex)
 	}
 	endptr = xlogreader->EndRecPtr;
 
+	pg_free(xlogreader->readBuf);
 	XLogReaderFree(xlogreader);
 	if (xlogreadfd != -1)
 	{
@@ -174,6 +178,7 @@ findLastCheckpoint(const char *datadir, XLogRecPtr forkptr, int tliIndex,
 	xlogreader = XLogReaderAllocate(WalSegSz);
 	if (xlogreader == NULL)
 		pg_fatal("out of memory");
+	xlogreader->readBuf = pg_malloc(XLOG_BLCKSZ);
 
 	searchptr = forkptr;
 	for (;;)
@@ -222,6 +227,7 @@ findLastCheckpoint(const char *datadir, XLogRecPtr forkptr, int tliIndex,
 		searchptr = record->xl_prev;
 	}
 
+	pg_free(xlogreader->readBuf);
 	XLogReaderFree(xlogreader);
 	if (xlogreadfd != -1)
 	{
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 56e2f8b0b0..bdf3c81b03 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -1108,6 +1108,7 @@ main(int argc, char **argv)
 	xlogreader_state = XLogReaderAllocate(WalSegSz);
 	if (!xlogreader_state)
 		fatal_error("out of memory");
+	xlogreader_state->readBuf = palloc(XLOG_BLCKSZ);
 
 	/* first find a valid recptr to start from */
 	first_record = XLogFindNextRecord(xlogreader_state, private.startptr,
@@ -1190,6 +1191,7 @@ main(int argc, char **argv)
 					(uint32) xlogreader_state->ReadRecPtr,
 					errormsg);
 
+	pfree(xlogreader_state->readBuf);
 	XLogReaderFree(xlogreader_state);
 
 	return EXIT_SUCCESS;
-- 
2.16.3

----Next_Part(Fri_Sep_06_16_33_18_2019_198)----