Use vectored I/O to fill new WAL segments.
Instead of making many block-sized write() calls to fill a new WAL file with zeroes, make a smaller number of pwritev() calls (or various emulations). The actual number depends on the OS's IOV_MAX, which PG_IOV_MAX currently caps at 32. That means we'll write 256kB per call on typical systems. We may want to tune the number later with more experience. Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/CA%2BhUKGJA%2Bu-220VONeoREBXJ9P3S94Y7J%2BkqCnTYmahvZJwM%3Dg%40mail.gmail.com
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@ -48,6 +48,7 @@
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#include "pg_trace.h"
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#include "pg_trace.h"
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#include "pgstat.h"
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#include "pgstat.h"
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#include "port/atomics.h"
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#include "port/atomics.h"
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#include "port/pg_iovec.h"
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#include "postmaster/bgwriter.h"
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#include "postmaster/bgwriter.h"
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#include "postmaster/startup.h"
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#include "postmaster/startup.h"
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#include "postmaster/walwriter.h"
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#include "postmaster/walwriter.h"
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@ -3270,7 +3271,6 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
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XLogSegNo installed_segno;
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XLogSegNo installed_segno;
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XLogSegNo max_segno;
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XLogSegNo max_segno;
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int fd;
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int fd;
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int nbytes;
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int save_errno;
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int save_errno;
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XLogFilePath(path, ThisTimeLineID, logsegno, wal_segment_size);
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XLogFilePath(path, ThisTimeLineID, logsegno, wal_segment_size);
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@ -3317,6 +3317,9 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
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save_errno = 0;
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save_errno = 0;
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if (wal_init_zero)
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if (wal_init_zero)
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{
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{
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struct iovec iov[PG_IOV_MAX];
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int blocks;
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/*
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/*
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* Zero-fill the file. With this setting, we do this the hard way to
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* Zero-fill the file. With this setting, we do this the hard way to
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* ensure that all the file space has really been allocated. On
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* ensure that all the file space has really been allocated. On
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@ -3326,15 +3329,28 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
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* indirect blocks are down on disk. Therefore, fdatasync(2) or
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* indirect blocks are down on disk. Therefore, fdatasync(2) or
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* O_DSYNC will be sufficient to sync future writes to the log file.
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* O_DSYNC will be sufficient to sync future writes to the log file.
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*/
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*/
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for (nbytes = 0; nbytes < wal_segment_size; nbytes += XLOG_BLCKSZ)
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/* Prepare to write out a lot of copies of our zero buffer at once. */
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for (int i = 0; i < lengthof(iov); ++i)
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{
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{
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errno = 0;
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iov[i].iov_base = zbuffer.data;
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if (write(fd, zbuffer.data, XLOG_BLCKSZ) != XLOG_BLCKSZ)
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iov[i].iov_len = XLOG_BLCKSZ;
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}
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/* Loop, writing as many blocks as we can for each system call. */
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blocks = wal_segment_size / XLOG_BLCKSZ;
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for (int i = 0; i < blocks;)
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{
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int iovcnt = Min(blocks - i, lengthof(iov));
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off_t offset = i * XLOG_BLCKSZ;
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if (pg_pwritev_with_retry(fd, iov, iovcnt, offset) < 0)
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{
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{
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/* if write didn't set errno, assume no disk space */
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save_errno = errno;
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save_errno = errno ? errno : ENOSPC;
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break;
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break;
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}
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}
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i += iovcnt;
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}
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}
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}
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}
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else
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else
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