On Mon, Mar 6, 2017 at 3:27 AM, Rushabh Lathia <rushabh.lat...@gmail.com> wrote: > Yes, I thought of adding wait event only for the sync but then recording the > wait event for both write and sync. I understand that OS level writes are > cheap but it still have some cost attached to that. Also I thought for the > monitoring tool being develop using this wait events, will have more useful > capture data if we try to collect as much info as we can. Or may be not. > > I am open for other opinion/suggestions.
Writes are NOT always fast. I've seen cases of write() blocking for LONG periods of time on systems that are in the process of failing, or just busy. So I think we certainly want to advertise a wait event for those. Likewise, I agree that the prefetch call probably SHOULDN'T block, but just because it shouldn't doesn't mean it never will. I think somebody should try a pgbench run with this patch applied, using a scale factor greater than shared_buffers, and generate a wait event profile, just to see if these are showing up and how often. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers