Bruce Momjian <[EMAIL PROTECTED]> wrote: > Is there anything to do for 8.2 here?
I'm working on Tom's idea. It is not a feature and does not change the on-disk-structures, so I hope it meet the 8.2 deadline... Tom Lane <[EMAIL PROTECTED]> 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. I added a subxid array to Snapshot and running subxids are gathered from PGPROC->subxids cache. There are two overflowed case; any of PGPROC->subxids are overflowed or the number of total subxids exceeds pre-allocated buffers. If overflowed, we cannot avoid to call SubTransGetTopmostTransaction. I tested the patch and did not see any context switch storm which comes from pg_subtrans, but there may be some bugs in the visibility checking. It would be very nice if you could review or test the patch. Regards, --- ITAGAKI Takahiro NTT Open Source Software Center
snapshot_subtrans.patch
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