Use PGAlignedXLogBlock for some code simplification

The code in BootStrapXLOG() and in pg_test_fsync.c tried to align WAL
buffers in complicated ways.  Also, they still used XLOG_BLCKSZ for
the alignment, even though that should now be PG_IO_ALIGN_SIZE.  This
can now be simplified and made more consistent by using
PGAlignedXLogBlock, either directly in BootStrapXLOG() and using
alignas in pg_test_fsync.c.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/f462a175-b608-44a1-b428-bdf351e914f4%40eisentraut.org

2 files changed, 8 insertions, 15 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 22d0a2e8c3a..89cbda9cc7c 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5089,7 +5089,7 @@ void
 BootStrapXLOG(uint32 data_checksum_version)
 {
 	CheckPoint	checkPoint;
-	char	   *buffer;
+	PGAlignedXLogBlock buffer;
 	XLogPageHeader page;
 	XLogLongPageHeader longpage;
 	XLogRecord *record;
@@ -5118,10 +5118,8 @@ BootStrapXLOG(uint32 data_checksum_version)
 	sysidentifier |= ((uint64) tv.tv_usec) << 12;
 	sysidentifier |= getpid() & 0xFFF;
 
-	/* page buffer must be aligned suitably for O_DIRECT */
-	buffer = (char *) palloc(XLOG_BLCKSZ + XLOG_BLCKSZ);
-	page = (XLogPageHeader) TYPEALIGN(XLOG_BLCKSZ, buffer);
-	memset(page, 0, XLOG_BLCKSZ);
+	memset(&buffer, 0, sizeof buffer);
+	page = (XLogPageHeader) &buffer;
 
 	/*
 	 * Set up information for the initial checkpoint record
@@ -5202,7 +5200,7 @@ BootStrapXLOG(uint32 data_checksum_version)
 	/* Write the first page with the initial record */
 	errno = 0;
 	pgstat_report_wait_start(WAIT_EVENT_WAL_BOOTSTRAP_WRITE);
-	if (write(openLogFile, page, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	if (write(openLogFile, &buffer, XLOG_BLCKSZ) != XLOG_BLCKSZ)
 	{
 		/* if write didn't set errno, assume problem is no disk space */
 		if (errno == 0)
@@ -5242,8 +5240,6 @@ BootStrapXLOG(uint32 data_checksum_version)
 	BootStrapSUBTRANS();
 	BootStrapMultiXact();
 
-	pfree(buffer);
-
 	/*
 	 * Force control file to be read - in contrast to normal processing we'd
 	 * otherwise never run the checks and GUC related initializations therein.
diff --git a/src/bin/pg_test_fsync/pg_test_fsync.c b/src/bin/pg_test_fsync/pg_test_fsync.c
index 0060ea15902..23f45a100e5 100644
--- a/src/bin/pg_test_fsync/pg_test_fsync.c
+++ b/src/bin/pg_test_fsync/pg_test_fsync.c
@@ -68,9 +68,8 @@ static const char *progname;
 
 static unsigned int secs_per_test = 5;
 static int	needs_unlink = 0;
-static char full_buf[DEFAULT_XLOG_SEG_SIZE],
-		   *buf,
-		   *filename = FSYNC_FILENAME;
+alignas(PGAlignedXLogBlock) static char buf[DEFAULT_XLOG_SEG_SIZE];
+static char *filename = FSYNC_FILENAME;
 static struct timeval start_t,
 			stop_t;
 static sig_atomic_t alarm_triggered = false;
@@ -232,9 +231,7 @@ prepare_buf(void)
 
 	/* write random data into buffer */
 	for (ops = 0; ops < DEFAULT_XLOG_SEG_SIZE; ops++)
-		full_buf[ops] = (char) pg_prng_int32(&pg_global_prng_state);
-
-	buf = (char *) TYPEALIGN(XLOG_BLCKSZ, full_buf);
+		buf[ops] = (char) pg_prng_int32(&pg_global_prng_state);
 }
 
 static void
@@ -248,7 +245,7 @@ test_open(void)
 	if ((tmpfile = open(filename, O_RDWR | O_CREAT | PG_BINARY, S_IRUSR | S_IWUSR)) == -1)
 		die("could not open output file");
 	needs_unlink = 1;
-	if (write(tmpfile, full_buf, DEFAULT_XLOG_SEG_SIZE) !=
+	if (write(tmpfile, buf, DEFAULT_XLOG_SEG_SIZE) !=
 		DEFAULT_XLOG_SEG_SIZE)
 		die("write failed");