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Introduce pg_pwrite_zeros() in fileutils.c

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This routine is designed to write zeros to a file using vectored I/O,
for a size given by its caller, being useful when it comes to
initializing a file with a final size already known.

XLogFileInitInternal() in xlog.c is changed to use this new routine when
initializing WAL segments with zeros (wal_init_zero enabled).  Note that
the aligned buffers used for the vectored I/O writes have a size of
XLOG_BLCKSZ, and not BLCKSZ anymore, as pg_pwrite_zeros() relies on
PGAlignedBlock while xlog.c originally used PGAlignedXLogBlock.

This routine will be used in a follow-up patch to do the pre-padding of
WAL segments for pg_receivewal and pg_basebackup when these are not
compressed.

Author: Bharath Rupireddy
Reviewed-by: Nathan Bossart, Andres Freund, Thomas Munro, Michael
Paquier
Discussion: https://www.postgresql.org/message-id/CALj2ACUq7nAb7%3DbJNbK3yYmp-SZhJcXFR_pLk8un6XgDzDF3OA%40mail.gmail.com
This commit is contained in:
Michael Paquier
2022-11-08 12:23:46 +09:00
parent d7744d50a5
commit 3bdbdf5d06
3 changed files with 80 additions and 28 deletions
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33
src/backend/access/transam/xlog.c
View File

@@ -2921,7 +2921,6 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
bool *added, char *path)
{
char tmppath[MAXPGPATH];
PGAlignedXLogBlock zbuffer;
XLogSegNo installed_segno;
XLogSegNo max_segno;
int fd;
@@ -2965,14 +2964,11 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
(errcode_for_file_access(),
errmsg("could not create file \"%s\": %m", tmppath)));
memset(zbuffer.data, 0, XLOG_BLCKSZ);
pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
save_errno = 0;
if (wal_init_zero)
{
struct iovec iov[PG_IOV_MAX];
int blocks;
ssize_t rc;
/*
* Zero-fill the file. With this setting, we do this the hard way to
@@ -2983,29 +2979,10 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
* indirect blocks are down on disk. Therefore, fdatasync(2) or
* O_DSYNC will be sufficient to sync future writes to the log file.
*/
rc = pg_pwrite_zeros(fd, wal_segment_size);
/* Prepare to write out a lot of copies of our zero buffer at once. */
for (int i = 0; i < lengthof(iov); ++i)
{
iov[i].iov_base = zbuffer.data;
iov[i].iov_len = XLOG_BLCKSZ;
}
/* Loop, writing as many blocks as we can for each system call. */
blocks = wal_segment_size / XLOG_BLCKSZ;
for (int i = 0; i < blocks;)
{
int iovcnt = Min(blocks - i, lengthof(iov));
off_t offset = i * XLOG_BLCKSZ;
if (pg_pwritev_with_retry(fd, iov, iovcnt, offset) < 0)
{
save_errno = errno;
break;
}
i += iovcnt;
}
if (rc < 0)
save_errno = errno;
}
else
{
@@ -3014,7 +2991,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
* enough.
*/
errno = 0;
if (pg_pwrite(fd, zbuffer.data, 1, wal_segment_size - 1) != 1)
if (pg_pwrite(fd, "\0", 1, wal_segment_size - 1) != 1)
{
/* if write didn't set errno, assume no disk space */
save_errno = errno ? errno : ENOSPC;