Re: [PATCH] Revert default wal_sync_method to fdatasync on Linux 2.6.33+

On 12/6/10 6:13 PM, Tom Lane wrote:
> Josh Berkus <josh(at)agliodbs(dot)com> writes:
>> OK, patch coming then. Right now test_fsync aborts when O_DIRECT fails.
>> What should I have it do instead?
>
> Report that it fails, and keep testing the other methods.

Patch attached. Includes a fair amount of comment cleanup, since
existing comments did not meet our current project standards. Tests all
6 of the methods we support separately.

Some questions, though:

(1) Why are we doing the open_sync different-size write test? AFAIK,
this doesn't match any behavior which PostgreSQL has.

(2) In this patch, I'm stepping down the number of loops which
fsync_writethrough does by 90%. The reason for that was that on the
platforms where I tested writethrough (desktop machines), doing 10,000
loops took 15-20 *minutes*, which seems hard on the user. Would be easy
to revert if you think it's a bad idea.
Possibly auto-sizing the number of loops based on the first fsync test
might be a good idea, but seems like going a bit too far.

(3) Should the multi-descriptor test be using writethrough on platforms
which support it?

--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com