Re: ["Stephen C. Tweedie" <sct@redhat.com>] Re: O_DSYNC flag for open

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Doug McNaught <doug(at)wireboard(dot)com> forwards:
> >> 2.4's O_SYNC actually does a fdatasync internally. This is also the
> >> default behaviour of HPUX, which requires you to set a sysctl variable
> >> if you want O_SYNC to flush timestamp changes to disk.
>
> Well, that guy might know all about Linux, but he doesn't know anything
> about HPUX (at least not any version I've ever run). O_SYNC is
> distinctly different from O_DSYNC around here.

Y'know, I figured that might be the case. ;) He's a well-respected
Linux filesystem hacker, so I trust him on the Linux stuff.

So are we still thinking about preallocating log files as a
performance hack? It does seem that using preallocated files along
with O_DATASYNC will eliminate pretty much all metadata writes under
Linux in future...

[NOT suggesting we try to add anything to 7.1, I'm eagerly awaiting RC1]

-Doug