Use pg_pwrite() in more places.

This removes some lseek() system calls.

Author: Thomas Munro
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/CA%2BhUKGJ%2BoHhnvqjn3%3DHro7xu-YDR8FPr0FL6LF35kHRX%3D_bUzg%40mail.gmail.com

Author: macdice

contrib/pg_stat_statements/pg_stat_statements.c

@@ -1868,12 +1868,9 @@ qtext_store(const char *query, int query_len,
 	if (fd < 0)
 		goto error;
 
-	if (lseek(fd, off, SEEK_SET) != off)
+	if (pg_pwrite(fd, query, query_len, off) != query_len)
 		goto error;
-
-	if (write(fd, query, query_len) != query_len)
-		goto error;
-	if (write(fd, "\0", 1) != 1)
+	if (pg_pwrite(fd, "\0", 1, off + query_len) != 1)
 		goto error;
 
 	CloseTransientFile(fd);

src/backend/access/heap/rewriteheap.c

@@ -1156,21 +1156,14 @@ heap_xlog_logical_rewrite(XLogReaderState *r)
 						path, (uint32) xlrec->offset)));
 	pgstat_report_wait_end();
 
-	/* now seek to the position we want to write our data to */
-	if (lseek(fd, xlrec->offset, SEEK_SET) != xlrec->offset)
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not seek to end of file \"%s\": %m",
-						path)));
-
 	data = XLogRecGetData(r) + sizeof(*xlrec);
 
 	len = xlrec->num_mappings * sizeof(LogicalRewriteMappingData);
 
 	/* write out tail end of mapping file (again) */
 	errno = 0;
 	pgstat_report_wait_start(WAIT_EVENT_LOGICAL_REWRITE_MAPPING_WRITE);
-	if (write(fd, data, len) != len)
+	if (pg_pwrite(fd, data, len, xlrec->offset) != len)
 	{
 		/* if write didn't set errno, assume problem is no disk space */
 		if (errno == 0)

src/backend/replication/walreceiver.c

@@ -85,14 +85,13 @@ WalReceiverFunctionsType *WalReceiverFunctions = NULL;
 #define NAPTIME_PER_CYCLE 100	/* max sleep time between cycles (100ms) */
 
 /*
- * These variables are used similarly to openLogFile/SegNo/Off,
+ * These variables are used similarly to openLogFile/SegNo,
  * but for walreceiver to write the XLOG. recvFileTLI is the TimeLineID
  * corresponding the filename of recvFile.
  */
 static int	recvFile = -1;
 static TimeLineID recvFileTLI = 0;
 static XLogSegNo recvSegNo = 0;
-static uint32 recvOff = 0;
 
 /*
  * Flags set by interrupt handlers of walreceiver for later service in the
@@ -945,7 +944,6 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 			use_existent = true;
 			recvFile = XLogFileInit(recvSegNo, &use_existent, true);
 			recvFileTLI = ThisTimeLineID;
-			recvOff = 0;
 		}
 
 		/* Calculate the start offset of the received logs */
@@ -956,29 +954,10 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 		else
 			segbytes = nbytes;
 
-		/* Need to seek in the file? */
-		if (recvOff != startoff)
-		{
-			if (lseek(recvFile, (off_t) startoff, SEEK_SET) < 0)
-			{
-				char		xlogfname[MAXFNAMELEN];
-				int			save_errno = errno;
-
-				XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
-				errno = save_errno;
-				ereport(PANIC,
-						(errcode_for_file_access(),
-						 errmsg("could not seek in log segment %s to offset %u: %m",
-								xlogfname, startoff)));
-			}
-
-			recvOff = startoff;
-		}
-
 		/* OK to write the logs */
 		errno = 0;
 
-		byteswritten = write(recvFile, buf, segbytes);
+		byteswritten = pg_pwrite(recvFile, buf, segbytes, (off_t) startoff);
 		if (byteswritten <= 0)
 		{
 			char		xlogfname[MAXFNAMELEN];
@@ -995,13 +974,12 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 					(errcode_for_file_access(),
 					 errmsg("could not write to log segment %s "
 							"at offset %u, length %lu: %m",
-							xlogfname, recvOff, (unsigned long) segbytes)));
+							xlogfname, startoff, (unsigned long) segbytes)));
 		}
 
 		/* Update state for write */
 		recptr += byteswritten;
 
-		recvOff += byteswritten;
 		nbytes -= byteswritten;
 		buf += byteswritten;
 

src/backend/utils/init/miscinit.c

@@ -1333,8 +1333,7 @@ AddToDataDirLockFile(int target_line, const char *str)
 	len = strlen(destbuffer);
 	errno = 0;
 	pgstat_report_wait_start(WAIT_EVENT_LOCK_FILE_ADDTODATADIR_WRITE);
-	if (lseek(fd, (off_t) 0, SEEK_SET) != 0 ||
-		(int) write(fd, destbuffer, len) != len)
+	if (pg_pwrite(fd, destbuffer, len, 0) != len)
 	{
 		pgstat_report_wait_end();
 		/* if write didn't set errno, assume problem is no disk space */