Date: Wed, 5 Mar 2014 08:17:07 +0100 From: Olav Gjerde <olav@backupbay.com> To: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> Cc: freebsd-fs@freebsd.org Subject: Re: Is LZ4 compression of the ZFS L2ARC available in any RELEASE/STABLE? Message-ID: <CAJ7kQyEp208XKt3CaiBufiB%2Bg_CHAkUgzAzVdX_6Gx2WyW1ENg@mail.gmail.com> In-Reply-To: <alpine.GSO.2.01.1403042037290.1717@freddy.simplesystems.org> 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> <alpine.GSO.2.01.1403042037290.1717@freddy.simplesystems.org>
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Currently I've set the recordsize to 8k, however I'm thinking maybe a recordsize of 4k may more optimal? This is because the compressratio with LZ4 is around 2.5 and this value has been constant for all my data while growing from a few megabytes to a tenfold of gigabytes. Maybe something I should play with to see if it makes a difference. On Wed, Mar 5, 2014 at 3:40 AM, Bob Friesenhahn < bfriesen@simple.dallas.tx.us> wrote: > On Tue, 4 Mar 2014, Olav Gjerde wrote: > > I managed to mess up who I replied to and Matthew replied back with a go= od >> 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/ > --=20 Olav Gr=F8n=E5s Gjerde
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