Use pg_pwrite() in pg_test_fsync.

For consistency with the PostgreSQL behavior this test program is
intended to simulate, use pwrite() instead of lseek() + write().

Also fix the final "non-sync" test, which was opening and closing the
file for every write.

Discussion: https://postgr.es/m/CA%2BhUKGJjjid2BJsvjMALBTduo1ogdx2SPYaTQL3wAy8y2hc4nw%40mail.gmail.com

src/bin/pg_test_fsync/pg_test_fsync.c

@@ -290,10 +290,11 @@ test_sync(int writes_per_op)
 		for (ops = 0; alarm_triggered == false; ops++)
 		{
 			for (writes = 0; writes < writes_per_op; writes++)
-				if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+				if (pg_pwrite(tmpfile,
+							  buf,
+							  XLOG_BLCKSZ,
+							  writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
 					die("write failed");
-			if (lseek(tmpfile, 0, SEEK_SET) == -1)
-				die("seek failed");
 		}
 		STOP_TIMER;
 		close(tmpfile);
@@ -315,11 +316,12 @@ test_sync(int writes_per_op)
 	for (ops = 0; alarm_triggered == false; ops++)
 	{
 		for (writes = 0; writes < writes_per_op; writes++)
-			if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+			if (pg_pwrite(tmpfile,
+						  buf,
+						  XLOG_BLCKSZ,
+						  writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
 				die("write failed");
 		fdatasync(tmpfile);
-		if (lseek(tmpfile, 0, SEEK_SET) == -1)
-			die("seek failed");
 	}
 	STOP_TIMER;
 	close(tmpfile);
@@ -339,12 +341,13 @@ test_sync(int writes_per_op)
 	for (ops = 0; alarm_triggered == false; ops++)
 	{
 		for (writes = 0; writes < writes_per_op; writes++)
-			if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+			if (pg_pwrite(tmpfile,
+						  buf,
+						  XLOG_BLCKSZ,
+						  writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
 				die("write failed");
 		if (fsync(tmpfile) != 0)
 			die("fsync failed");
-		if (lseek(tmpfile, 0, SEEK_SET) == -1)
-			die("seek failed");
 	}
 	STOP_TIMER;
 	close(tmpfile);
@@ -362,12 +365,13 @@ test_sync(int writes_per_op)
 	for (ops = 0; alarm_triggered == false; ops++)
 	{
 		for (writes = 0; writes < writes_per_op; writes++)
-			if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+			if (pg_pwrite(tmpfile,
+						  buf,
+						  XLOG_BLCKSZ,
+						  writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
 				die("write failed");
 		if (pg_fsync_writethrough(tmpfile) != 0)
 			die("fsync failed");
-		if (lseek(tmpfile, 0, SEEK_SET) == -1)
-			die("seek failed");
 	}
 	STOP_TIMER;
 	close(tmpfile);
@@ -393,8 +397,10 @@ test_sync(int writes_per_op)
 		for (ops = 0; alarm_triggered == false; ops++)
 		{
 			for (writes = 0; writes < writes_per_op; writes++)
-				if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
-
+				if (pg_pwrite(tmpfile,
+							  buf,
+							  XLOG_BLCKSZ,
+							  writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
 					/*
 					 * This can generate write failures if the filesystem has
 					 * a large block size, e.g. 4k, and there is no support
@@ -402,8 +408,6 @@ test_sync(int writes_per_op)
 					 * size, e.g. XFS.
 					 */
 					die("write failed");
-			if (lseek(tmpfile, 0, SEEK_SET) == -1)
-				die("seek failed");
 		}
 		STOP_TIMER;
 		close(tmpfile);
@@ -457,11 +461,12 @@ test_open_sync(const char *msg, int writes_size)
 		for (ops = 0; alarm_triggered == false; ops++)
 		{
 			for (writes = 0; writes < 16 / writes_size; writes++)
-				if (write(tmpfile, buf, writes_size * 1024) !=
+				if (pg_pwrite(tmpfile,
+							  buf,
+							  writes_size * 1024,
+							  writes * writes_size * 1024) !=
 					writes_size * 1024)
 					die("write failed");
-			if (lseek(tmpfile, 0, SEEK_SET) == -1)
-				die("seek failed");
 		}
 		STOP_TIMER;
 		close(tmpfile);
@@ -553,16 +558,16 @@ test_non_sync(void)
 	printf(LABEL_FORMAT, "write");
 	fflush(stdout);
 
+	if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
+		die("could not open output file");
 	START_TIMER;
 	for (ops = 0; alarm_triggered == false; ops++)
 	{
-		if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
-			die("could not open output file");
-		if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+		if (pg_pwrite(tmpfile, buf, XLOG_BLCKSZ, 0) != XLOG_BLCKSZ)
 			die("write failed");
-		close(tmpfile);
 	}
 	STOP_TIMER;
+	close(tmpfile);
 }
 
 static void