On Wed, 2007-01-24 at 09:32 +0530, Pavan Deolasee wrote: > On a typical desktop class 2 CPU Dell machine, we have seen pgbench > clocking more than 1500 tps. That implies CLOG would get filled up in > less > than 262144/1500=174 seconds. VACUUM on accounts table takes much > longer to trigger.
You assume that all of the top level transactions have no subtransactions. On that test, subtransactions are in use because of the EXCEPTION clause in the PL/pgSQL used. That should at least double the number of Xids. > So > most of the 636528 reads in the next 55 minutes can be attributed to > VACUUM. A similar argument might also be applied to subtrans, so a similar investigation seems worthwhile. Subtrans has space for less Xids than clog, BTW. OTOH, I do think that 99% of that will not cause I/O. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
