Horton

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

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Josh Berkus <josh@agliodbs.com>
Cc: Greg Smith <greg@2ndquadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2010-12-07T02:05:28Z
Lists: pgsql-hackers 
On Mon, Dec 6, 2010 at 9:04 PM, Josh Berkus <josh@agliodbs.com> wrote:
>
>> Mac OS X:  Like Solaris, there's a similar mechanism but it's not
>> O_DIRECT; see
>> http://stackoverflow.com/questions/2299402/how-does-one-do-raw-io-on-mac-os-x-ie-equivalent-to-linuxs-o-direct-flag
>> for notes about the F_NOCACHE  feature used.  Same basic situation as
>> Solaris; there's an API, but PostgreSQL doesn't use it yet.
>
> Actually, on OSX 10.5.8, o_dsync and fdatasync aren't even available.
> From my run, it looks like even so regular fsync might be better than
> open_sync.

But I think you need to use fsync_writethrough if you actually want durability.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company