On Tue, Sep 29, 2015 at 1:01 PM, Benjamin Smith <ben@chico.com> wrote:
Does anybody here have any recommendations for using PostgreSQL 9.4 (latest) with ZFS?
We've been running both on ZFS/CentOS 6 with excellent results, and are considering putting the two together. In particular, the CoW nature (and subsequent fragmentation/thrashing) of ZFS becomes largely irrelevant on SSDs; the very act of wear leveling on an SSD is itself a form of intentional thrashing that doesn't affect performance since SSDs have no meaningful seek time. It would seem that PGCon 2013 even had a workshop on it! https://www.pgcon.org/2013/schedule/events/612.en.html
The exact configuration we're contemplating is either (3x 400 RAIDZ1) or (4x 400 RAIDZ2) with Intel Enterprise SATA3 SSDs, with default (lz4) compression enabled.
If this is a particularly good or bad idea, I'd like to hear it, and why?
We've run postgres on ZFS for years with great success (first on OpenSolaris, now on OmniOS, and I personally run it on FreeBSD). The snapshotting feature makes upgrades on large clusters much less scary (snapshot and revert if it goes bad) and being able to bring a snapshot backup up as a clone to restore an accidentally dropped table is great.
Others have given a lot of great advice as far as system tuning. Only other thing I can add is you definitely do want your data directory on its own pool. But I recommend putting the actual data in a folder under that pool (possibly by major version name). For example if your pool is
/data/postgres
Create a folder under that directory to actually put the data:
mkdir /data/postgres/9.4
This allows pg_upgrade's --link option to work during major upgrades since you can't have an upgrade destination on a different filesystem. Just make a 9.5 directory in the same spot when the time comes around. With ZFS snapshots available, there's really no reason not to use the --link option to greatly speed up upgrades.
-- Keith Fiske Database Administrator OmniTI Computer Consulting, Inc. http://www.keithf4.com
