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Support direct I/O on macOS.

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Macs don't understand O_DIRECT, but they can disable caching with a
separate fcntl() call.  Extend the file opening functions in fd.c to
handle this for us if the caller passes in PG_O_DIRECT.

For now, this affects only WAL data and even then only if you set:

  max_wal_senders=0
  wal_level=minimal

This is not expected to be very useful on its own, but later proposed
patches will make greater use of direct I/O, and it'll be useful for
testing if developers on Macs can see the effects.

Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKG%2BADiyyHe0cun2wfT%2BSVnFVqNYPxoO6J9zcZkVO7%2BNGig%40mail.gmail.com
This commit is contained in:
Thomas Munro
2021-07-19 08:52:00 +12:00
parent f157db8622
commit 2dbe890571
4 changed files with 83 additions and 19 deletions
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35
src/bin/pg_test_fsync/pg_test_fsync.c
View File

@@ -217,8 +217,10 @@ handle_args(int argc, char *argv[])
"%u seconds per test\n",
secs_per_test),
secs_per_test);
#if PG_O_DIRECT != 0
#if defined(O_DIRECT)
printf(_("O_DIRECT supported on this platform for open_datasync and open_sync.\n"));
#elif defined(F_NOCACHE)
printf(_("F_NOCACHE supported on this platform for open_datasync and open_sync.\n"));
#else
printf(_("Direct I/O is not supported on this platform.\n"));
#endif
@@ -258,6 +260,31 @@ test_open(void)
close(tmpfile);
}
static int
open_direct(const char *path, int flags, mode_t mode)
{
int fd;
#ifdef O_DIRECT
flags |= O_DIRECT;
#endif
fd = open(path, flags, mode);
#if !defined(O_DIRECT) && defined(F_NOCACHE)
if (fd >= 0 && fcntl(fd, F_NOCACHE, 1) < 0)
{
int save_errno = errno;
close(fd);
errno = save_errno;
return -1;
}
#endif
return fd;
}
static void
test_sync(int writes_per_op)
{
@@ -279,7 +306,7 @@ test_sync(int writes_per_op)
fflush(stdout);
#ifdef OPEN_DATASYNC_FLAG
if ((tmpfile = open(filename, O_RDWR | O_DSYNC | PG_O_DIRECT | PG_BINARY, 0)) == -1)
if ((tmpfile = open_direct(filename, O_RDWR | O_DSYNC | PG_BINARY, 0)) == -1)
{
printf(NA_FORMAT, _("n/a*"));
fs_warning = true;
@@ -386,7 +413,7 @@ test_sync(int writes_per_op)
fflush(stdout);
#ifdef OPEN_SYNC_FLAG
if ((tmpfile = open(filename, O_RDWR | OPEN_SYNC_FLAG | PG_O_DIRECT | PG_BINARY, 0)) == -1)
if ((tmpfile = open_direct(filename, O_RDWR | OPEN_SYNC_FLAG | PG_BINARY, 0)) == -1)
{
printf(NA_FORMAT, _("n/a*"));
fs_warning = true;
@@ -454,7 +481,7 @@ test_open_sync(const char *msg, int writes_size)
fflush(stdout);
#ifdef OPEN_SYNC_FLAG
if ((tmpfile = open(filename, O_RDWR | OPEN_SYNC_FLAG | PG_O_DIRECT | PG_BINARY, 0)) == -1)
if ((tmpfile = open_direct(filename, O_RDWR | OPEN_SYNC_FLAG | PG_BINARY, 0)) == -1)
printf(NA_FORMAT, _("n/a*"));
else
{