Re: We really ought to do something about O_DIRECT and data=journalled on ext4

On 11/30/2010 11:17 PM, Tom Lane wrote:
> Andrew Dunstan<andrew(at)dunslane(dot)net> writes:
>> On 11/30/2010 10:09 PM, Tom Lane wrote:
>>> We should wait for the outcome of the discussion about whether to change
>>> the default wal_sync_method before worrying about this.
>> we've just had a significant PGX customer encounter this with the latest
>> Postgres on Redhat's freshly released flagship product. Presumably the
>> default wal_sync_method will only change prospectively.
> I don't think so. The fact that Linux is changing underneath us is a
> compelling reason for back-patching a change here. Our older branches
> still have to be able to run on modern OS versions. I'm also fairly
> unclear on what you think a fix would look like if it's not effectively
> a change in the default.
>
> (Hint: this *will* be changing, one way or another, in Red Hat's version
> of 8.4, since that's what RH is shipping in RHEL6.)
>
>

Well, my initial idea was that if PG_O_DIRECT is non-zero, we should
test at startup time if we can use it on the WAL file system and inhibit
its use if not.

Incidentally, I notice it's not used at all in test_fsync.c - should it
not be?

cheers

andrew