Tom Lane wrote: > I'm wondering about doing something similar to what > TransactionIdIsInProgress does, ie, make use of the PGPROC lists > of live subtransactions. Suppose that GetSnapshotData copies not > only top xids but live subxids into the snapshot, and adds a flag > indicating whether the subxids are complete (ie, none of the subxid > lists have overflowed). Then if the flag is set, tqual.c doesn't > need to do SubTransGetTopmostTransaction() before searching the > list.
Well, that sounds awfully more expensive than setting local-to-my-database Xmins as well as global (all databases) Xmins :-) On the other hand, ISTM as soon as one cache overflows, you have to go check pg_subtrans which means the entire optimization buys nothing in that case. It would be nice if the optimization degraded more gracefully. I don't have any concrete suggestion though. The changes proposed in the other CS-storm thread by the NTT person may help. -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
