On Wed, Mar 7, 2012 at 3:04 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Alvaro Herrera <alvhe...@commandprompt.com> writes: >> Just to keep things in perspective -- For a commit record to reach one >> megabyte, it would have to be a transaction that drops over 43k tables. >> Or have 64k smgr inval messages (for example, a TRUNCATE might send half >> a dozen of these messages). Or have 262k subtransactions. Or >> combinations thereof. > >> Now admittedly, a page is only 8 kB, so for a commit record to be "many >> pages long" (that is, >=3) it would require about 1500 smgr inval >> messages, or, say, about 250 TRUNCATEs (of permanent tables with at >> least one toastable field and at least one index). > > What about the locks (if running hot-standby)?
It's a list of active AccessExclusiveLocks. If that list is long you can be sure not much else is happening on the server. >> So they are undoubtely rare. Not sure if as rare as Higgs bosons. > > Even if they're rare, having a major performance hiccup when one happens > is not a side-effect I want to see from a patch whose only reason to > exist is better performance. I agree the effect you point out can exist, I just don't want to slow down the main case as a result. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
