On Mon, Jun 19, 2017 at 10:49:59AM -0500, Merlin Moncure wrote: > On Mon, Jun 19, 2017 at 10:36 AM, Jeff Janes <jeff.janes@xxxxxxxxx> wrote: > > If you have a RAID, set it to the number of spindles in your RAID and forget > > it. It is usually one of the less interesting knobs to play with. (Unless > > your usage pattern of the database is unusual and exact fits the above > > pattern.) > > Isn't that advice obsolete in a SSD world though? I was able to show > values up to 256 for a single device provided measurable gains for a > single S3500. It's true though that the class of queries that this > would help is pretty narrow. Our developer docs are much clearer: https://www.postgresql.org/docs/10/static/runtime-config-resource.html#runtime-config-resource-disk For magnetic drives, a good starting point for this setting is the number of separate drives comprising a RAID 0 stripe or RAID 1 mirror being used for the database. (For RAID 5 the parity drive should not be counted.) However, if the database is often busy with multiple queries issued in concurrent sessions, lower values may be sufficient to keep the disk array busy. A value higher than needed to keep the disks busy will only result in extra CPU overhead. SSDs and other memory-based storage can often process many concurrent requests, so the best value might be in the hundreds. I didn't backpatch this change since the original docs were not incorrect. -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription + -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
