On 10/1/15 8:04 PM, Joseph Kregloh wrote:
In either case you are still "bottlenecked" by the speed of the write from RAM to the zpool. Now for a small database with not many writes a ZIL would be awesome. But on a write heavy database you will be acknowledging more writes because of the ZIL that what you are physically able to write from RAM to zpool, thereby degrading performance.
Unless ZFS lies about fsync, you'll have to wait for writes to go somewhere, either the main pool or the ZIL. Because the ZIL is effectively write-only, having a ZIL could significantly reduce fsync latency because it's a) only writing and b) writing sequentially.
Essentially, it's the same idea as having a separate pg_xlog partition (except that depending on your setup there may well be pg_xlog read activity as well).
-- Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX Experts in Analytics, Data Architecture and PostgreSQL Data in Trouble? Get it in Treble! http://BlueTreble.com -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
