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