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Re: What happened to open_sync_without_odirect?

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: What happened to open_sync_without_odirect?
Date: 2011-01-16 20:12:11
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On 1/15/11 4:30 PM, Bruce Momjian wrote:
> Josh Berkus wrote:
>> Last I remember, we were going to add this as an option.  But I don't
>> see a patch in the queue.  Am I missing it?  Was I supposed to write it?
> I don't know, but let me add that I am confused how this would look to
> users.  In many cases, kernels don't even support O_DIRECT, so what
> would we do to specify this?  What about just auto-disabling O_DIRECT if
> the filesystem does not support it; maybe issue a log message about it.

Yes, you *are* confused.  The problem isn't auto-disabling, we already
do that.  The problem is *auto-enabling*; ages ago we made the
assumption that if o_sync was supported, so was o_direct.  We've now
found out that's not true on all platforms.

Also, test results show that even when supported, o_direct isn't
necessarily a win.  Hence, the additional fsync_method options.

                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.

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