waldirect.patch

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 266c0de..a830a01 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -122,6 +122,7 @@ const struct config_enum_entry sync_method_options[] = {
 #ifdef OPEN_DATASYNC_FLAG
 	{"open_datasync", SYNC_METHOD_OPEN_DSYNC, false},
 #endif
+	{"open_direct", SYNC_METHOD_OPEN_DIRECT, false},
 	{NULL, 0, false}
 };
 
@@ -1925,7 +1926,8 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible, bool xlog_switch)
 		 * fsync more than one file.
 		 */
 		if (sync_method != SYNC_METHOD_OPEN &&
-			sync_method != SYNC_METHOD_OPEN_DSYNC)
+			sync_method != SYNC_METHOD_OPEN_DSYNC &&
+			sync_method != SYNC_METHOD_OPEN_DIRECT)
 		{
 			if (openLogFile >= 0 &&
 				!XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
@@ -8958,6 +8960,15 @@ get_sync_bit(int method)
 		case SYNC_METHOD_OPEN_DSYNC:
 			return OPEN_DATASYNC_FLAG | o_direct_flag;
 #endif
+       case SYNC_METHOD_OPEN_DIRECT:
+			/*
+			 * Open the log with O_DIRECT flag only.  O_DIRECT guarantees
+			 * that data is written to disk when the IO completes if and
+			 * only if the file is fully allocated.  Fortunately, the log
+			 * files are always fully allocated by XLogFileInit() (or are
+			 * recycled from a fully-allocated log).
+			 */
+			return O_DIRECT;
 		default:
 			/* can't happen (unless we are out of sync with option array) */
 			elog(ERROR, "unrecognized wal_sync_method: %d", method);
@@ -9031,6 +9042,7 @@ issue_xlog_fsync(int fd, uint32 log, uint32 seg)
 #endif
 		case SYNC_METHOD_OPEN:
 		case SYNC_METHOD_OPEN_DSYNC:
+		case SYNC_METHOD_OPEN_DIRECT:
 			/* write synced it already */
 			break;
 		default:
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 400c52b..97acde5 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -564,3 +564,4 @@
 #------------------------------------------------------------------------------
 
 # Add settings for extensions here
+wal_sync_method = open_direct
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index f8aecef..b888ee7 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -83,6 +83,7 @@ typedef struct XLogRecord
 #define SYNC_METHOD_OPEN		2		/* for O_SYNC */
 #define SYNC_METHOD_FSYNC_WRITETHROUGH	3
 #define SYNC_METHOD_OPEN_DSYNC	4		/* for O_DSYNC */
+#define SYNC_METHOD_OPEN_DIRECT	5		/* for O_DIRECT */
 extern int	sync_method;
 
 /*