"Pavan Deolasee" <[EMAIL PROTECTED]> writes: > On 3/31/07, Tom Lane <[EMAIL PROTECTED]> wrote: >> Can you give a specific example?
> txn1 - CREATE INDEX CONCURRENTLY (takes ShareUpdateExclusiveLock) > txn2 - VACUUM ANALYZE (waits on ShareUpdateExclusiveLock) > tnx1 - waits for txn2 to complete in the second phase of CIC Oh, it's the cleanup wait you're worried about. > Lazy VACUUM is safe because we don't include "inVacuum" transactions > in the snapshot and hence don't wait for it in CIC. Hmm ... only if it's already set inVacuum true ... there's a window where it has not. I wonder whether we could change CIC so that the "reference snapshot" lists only transactions that are running and have already determined their serializable snapshot (ie, have set proc->xmin). Xacts that haven't yet done that can be ignored because they couldn't possibly see the dead tuples we're worried about, no? Then we could rearrange the order of operations in vacuum_rel so that we lock the target rel before we acquire a snapshot. Then a vacuum waiting for the CIC cannot cause a deadlock. Multi-rel CLUSTER could be changed the same way. I'm not particularly worried about single-rel CLUSTER, only stuff that would be reasonable to launch from background maintenance tasks. [ thinks... ] Actually, it seems risky to omit xids from the reference snapshot; that could perhaps screw up the index insertions. But we could look in the procArray to see if the xid still exists and has set an xmin before we actually wait for it. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly