Date: Tue, 4 Mar 2014 20:40:37 -0600 (CST) From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> To: Olav Gjerde <olav@backupbay.com> Cc: freebsd-fs@freebsd.org Subject: Re: Is LZ4 compression of the ZFS L2ARC available in any RELEASE/STABLE? Message-ID: <alpine.GSO.2.01.1403042037290.1717@freddy.simplesystems.org> In-Reply-To: <CAJ7kQyFf19Un_TS=kW=T21HT%2BoabhsUhJij5oixQ2_uh0LvHRA@mail.gmail.com> References: <CAJ7kQyGTOuynOoLukXbP2E6GPKRiBWx8_mLEchk90WDKO%2Bo-SA@mail.gmail.com> <53157CC2.8080107@FreeBSD.org> <CAJ7kQyGQjf_WbY64bLVX=YfmJUfAd8i22kVbVhZhEWPMg7bbQw@mail.gmail.com> <5315D446.3040701@freebsd.org> <CAJ7kQyFf19Un_TS=kW=T21HT%2BoabhsUhJij5oixQ2_uh0LvHRA@mail.gmail.com>
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On Tue, 4 Mar 2014, Olav Gjerde wrote: > I managed to mess up who I replied to and Matthew replied back with a good > answer which I think didn't reach the mailing list. > > I actually have a problem with query performance in one of my databases > related to running PostgreSQL on ZFS. Which is why I'm so interested in > compression for the L2ARC Cache. The problem is random IO read were > creating a report were I aggregate 75000 rows takes 30 minutes!!! The table > that I query has 400 million rows though. > The dataset easily fit in memory, so if I run the same query again it takes > less than a second. Make sure that your database is on a filesystem with zfs block-size matching the database block-size (rather than 128K). Otherwise far more data may be read than needed, and likewise, writes may result in writing far more data than needed. Regardless, L2ARC on SSD is a very good idea for this case. Bob -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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