From: Mel Llaguno <mllaguno@coverity.com>
To: desmodemone <desmodemone@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: HFS+ pg_test_fsync performance
Date: Tue, 15 Apr 2014 14:31:05 +0000
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My 2 cents :
The results are not surprising, in the linux enviroment the i/o call of pg_test_fsync are using O_DIRECT (PG_O_DIRECT) with also the O_SYNC or O_DSYNC calls, so ,in practice, it is waiting the "answer" from the storage bypassing the cache in sync mode, while in the Mac OS X it is not doing so, it's only using the O_SYNC or O_DSYNC calls without O_DIRECT, in practice, it's using the cache of filesystem , even if it is asking the sync of io calls.
Bye
Mat Dba
--------
Thanks for the explanation. Given that OSX always seems to use filesystem cache, is there a way to measure fsync performance that is equivalent to Linux? Or will the use of pg_test_fsync always be inflated under OSX? The reason I ask is that we would like to make a case with a customer that PG performance on OSX/HFS+ would be sub-optimal compared to using Linux/EXT4 (or FreeBSD/UFS2 for that matter).
Thanks, Mel
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To: pgsql-performance@postgresql.org
Cc: mllaguno@coverity.com, desmodemone@gmail.com
Subject: Re: HFS+ pg_test_fsync performance
In-Reply-To: <e36bb23bb5f9457ebee6bee8c767ca23@BN1PR05MB009.namprd05.prod.outlook.com>
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