Re: WAL and O_DIRECT

Ravi Krishna <s.ravikrishna@aim.com> writes:
> Why is O_DIRECT not used,
despite the documentation mentioning otherwise?

You've not shown us all your
settings, but this comment in xlog.c might
explain it:
    * Optimize
writes by bypassing kernel cache with O_DIRECT when using    * O_SYNC/O_FSYNC
and O_DSYNC.  But only if archiving and streaming are    * disabled,
otherwise the archive command or walsender process will read    * the WAL
soon after writing it, which is guaranteed to cause a physical    * read if
we bypassed the kernel cache. We also skip the    *
posix_fadvise(POSIX_FADV_DONTNEED) call in XLogFileClose() for the same    *
reason.
		regards, tom lane