"Pavan Deolasee" <[EMAIL PROTECTED]> writes: > When I looked at the code, it occurred to me that possibly we are > OK with just taking shared lock on the procarray. That means that > some other transaction can concurrently set its serializable snapshot > while we are scanning the procarray. But that should not harm us: > if we see the snapshot set, we wait for the transaction. A transaction > which is setting its serializable snapshot NOW, can not see the > tuples that we did not index, isn't it ?
[ itch... ] The problem is with time-extended execution of GetSnapshotData; what happens if the other guy lost the CPU for a good long time while in the middle of GetSnapshotData? He might set his xmin based on info you saw as long gone. You might be correct that it's safe, but the argument would have to hinge on the OldestXmin process being unable to commit because of someone holding shared ProcArrayLock; a point you are definitely not making above. (Study the comments in GetSnapshotData for awhile, also those in xact.c's commit-related code.) I'm about to head to bed and am certainly in no condition to carry the proof through. Have at it ... regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org