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Improve copydir() code for the case that fsync is off.

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We should avoid calling sync_file_range or posix_fadvise in this case,
since (a) we don't really care if the data gets synced, and might as
well save the kernel calls; (b) at least on Linux we know that the
kernel might block us until it's scheduled the write.

Also, avoid making a useless second traversal of the directory tree
if we're not actually going to call fsync(2) after all.
This commit is contained in:
Tom Lane 2012-07-21 20:10:29 -04:00
parent 2c4f5b4bc5
commit 2d46a57ddc
2 changed files with 15 additions and 7 deletions
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8
src/backend/storage/file/copydir.c
View File

@ -98,7 +98,11 @@ copydir(char *fromdir, char *todir, bool recurse)
/*
* Be paranoid here and fsync all files to ensure the copy is really done.
* But if fsync is disabled, we're done.
*/
if (!enableFsync)
return;
xldir = AllocateDir(todir);
if (xldir == NULL)
ereport(ERROR,
@ -200,9 +204,9 @@ copy_file(char *fromfile, char *tofile)
/*
* We fsync the files later but first flush them to avoid spamming the
* cache and hopefully get the kernel to start writing them out before
* the fsync comes.
* the fsync comes. Ignore any error, since it's only a hint.
*/
pg_flush_data(dstfd, offset, nbytes);
(void) pg_flush_data(dstfd, offset, nbytes);
}
if (close(dstfd))

14
src/backend/storage/file/fd.c
View File

@ -337,18 +337,22 @@ pg_fdatasync(int fd)
* pg_flush_data --- advise OS that the data described won't be needed soon
*
* Not all platforms have sync_file_range or posix_fadvise; treat as no-op
* if not available.
* if not available. Also, treat as no-op if enableFsync is off; this is
* because the call isn't free, and some platforms such as Linux will actually
* block the requestor until the write is scheduled.
*/
int
pg_flush_data(int fd, off_t offset, off_t amount)
{
if (enableFsync)
{
#if defined(HAVE_SYNC_FILE_RANGE)
return sync_file_range(fd, offset, amount, SYNC_FILE_RANGE_WRITE);
return sync_file_range(fd, offset, amount, SYNC_FILE_RANGE_WRITE);
#elif defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
return posix_fadvise(fd, offset, amount, POSIX_FADV_DONTNEED);
#else
return 0;
return posix_fadvise(fd, offset, amount, POSIX_FADV_DONTNEED);
#endif
}
return 0;
}