1 files changed, 12 insertions, 14 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index e9a66aa7062..651b0f3a84d 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -3182,8 +3182,7 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 {
 	char		path[MAXPGPATH];
 	char		tmppath[MAXPGPATH];
-	char		zbuffer_raw[XLOG_BLCKSZ + MAXIMUM_ALIGNOF];
-	char	   *zbuffer;
+	PGAlignedXLogBlock zbuffer;
 	XLogSegNo	installed_segno;
 	XLogSegNo	max_segno;
 	int			fd;
@@ -3237,17 +3236,13 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
 	 * fsync below) that all the indirect blocks are down on disk.  Therefore,
 	 * fdatasync(2) or O_DSYNC will be sufficient to sync future writes to the
 	 * log file.
-	 *
-	 * Note: ensure the buffer is reasonably well-aligned; this may save a few
-	 * cycles transferring data to the kernel.
 	 */
-	zbuffer = (char *) MAXALIGN(zbuffer_raw);
-	memset(zbuffer, 0, XLOG_BLCKSZ);
+	memset(zbuffer.data, 0, XLOG_BLCKSZ);
 	for (nbytes = 0; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
 	{
 		errno = 0;
 		pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
-		if ((int) write(fd, zbuffer, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
+		if ((int) write(fd, zbuffer.data, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
 		{
 			int			save_errno = errno;
 
@@ -3355,7 +3350,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 {
 	char		path[MAXPGPATH];
 	char		tmppath[MAXPGPATH];
-	char		buffer[XLOG_BLCKSZ];
+	PGAlignedXLogBlock buffer;
 	int			srcfd;
 	int			fd;
 	int			nbytes;
@@ -3399,7 +3394,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 		 * zeros.
 		 */
 		if (nread < sizeof(buffer))
-			memset(buffer, 0, sizeof(buffer));
+			memset(buffer.data, 0, sizeof(buffer));
 
 		if (nread > 0)
 		{
@@ -3407,7 +3402,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 				nread = sizeof(buffer);
 			errno = 0;
 			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
-			if (read(srcfd, buffer, nread) != nread)
+			if (read(srcfd, buffer.data, nread) != nread)
 			{
 				if (errno != 0)
 					ereport(ERROR,
@@ -3423,7 +3418,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
 		}
 		errno = 0;
 		pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_WRITE);
-		if ((int) write(fd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
+		if ((int) write(fd, buffer.data, sizeof(buffer)) != (int) sizeof(buffer))
 		{
 			int			save_errno = errno;
 
@@ -6410,8 +6405,11 @@ StartupXLOG(void)
 	xlogreader->system_identifier = ControlFile->system_identifier;
 
 	/*
-	 * Allocate pages dedicated to WAL consistency checks, those had better be
-	 * aligned.
+	 * Allocate two page buffers dedicated to WAL consistency checks.  We do
+	 * it this way, rather than just making static arrays, 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() will provide MAXALIGN'd storage.
 	 */
 	replay_image_masked = (char *) palloc(BLCKSZ);
 	master_image_masked = (char *) palloc(BLCKSZ);