Andres Freund wrote: > On 2016-07-20 11:26:11 -0400, Robert Haas wrote: > > On Wed, Jul 20, 2016 at 3:39 AM, Andres Freund <and...@anarazel.de> wrote: > > >>I think Snapshot's members whenTaken and lsn are updated/initialized > > >>only in GetSnapshotData(). So if GetSnapshotData() is not used, how > > >>will you expect those fields to be updated. We need those fields to > > >>be updated for TestForOldSnapshot(). > > > > > > That's why I suggested copying them from the current mvcc snapshot. > > > > And how do you obtain that? The functions that reference > > SnapshotToast are toast_delete_datum, toastrel_value_exists, and > > toast_fetch_datum, toast_fetch_datum_slice, but none of those take a > > snapshot as an argument, nor is there any reasonable way to make them > > do so. Those are indirectly called by things like bttextcmp, which > > don't know what snapshot was used to fetch the datum that they are > > detoasting and can't reasonably be made to know. > > > > I mean, you could do something *approximately* correct by calling > > GetActiveSnapshot() but that doesn't seem likely to be correct in > > detail. > > GetActiveSnapshot() seems like it should work well enough in this case, > or we could use pairingheap_first() to get the actual oldest registered > one.
Hmm. Why is the active snapshot not sufficient? Perhaps we need some kind of redesign or minor tweak to snapmgr to keep track of the oldest snapshot of a resowner or something like that? -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
