On Wed, Jul 13, 2022 at 8:59 PM Amit Langote <amitlangot...@gmail.com> wrote: > On Sat, Jul 9, 2022 at 1:15 AM Robert Haas <robertmh...@gmail.com> wrote: > Thanks for taking a look at this. I'll try to respond to other points > in a separate email, but I wanted to clarify something about below: > > > I find my ego slightly wounded by the comment that "the partition > > descriptor machinery has a hack that assumes that the queries > > originating in this module push the latest snapshot in the > > transaction-snapshot mode." It's true that the partition descriptor > > machinery gives different answers depending on the active snapshot, > > but, err, is that a hack, or just a perfectly reasonable design > > decision? > > I think my calling it a hack of "partition descriptor machinery" is > not entirely fair (sorry), because it's talking about the following > comment in find_inheritance_children_extended(), which describes it as > being a hack, so I mentioned the word "hack" in my comment too: > > /* > * Cope with partitions concurrently being detached. When we see a > * partition marked "detach pending", we omit it from the returned set > * of visible partitions if caller requested that and the tuple's xmin > * does not appear in progress to the active snapshot. (If there's no > * active snapshot set, that means we're not running a user query, so > * it's OK to always include detached partitions in that case; if the > * xmin is still running to the active snapshot, then the partition > * has not been detached yet and so we include it.) > * > * The reason for this hack is that we want to avoid seeing the > * partition as alive in RI queries during REPEATABLE READ or > * SERIALIZABLE transactions: such queries use a different snapshot > * than the one used by regular (user) queries. > */ > > That bit came in to make DETACH CONCURRENTLY produce sane answers for > RI queries in some cases. > > I guess my comment should really have said something like: > > HACK: find_inheritance_children_extended() has a hack that assumes > that the queries originating in this module push the latest snapshot > in transaction-snapshot mode.
Posting a new version with this bit fixed; cfbot complained that 0002 needed a rebase over 3592e0ff98. I will try to come up with a patch to enhance the PartitionDirectory interface to allow passing the snapshot to use when scanning pg_inherits explicitly, so we won't need the above "hack". -- Thanks, Amit Langote EDB: http://www.enterprisedb.com
v3-0002-Avoid-using-an-SQL-query-for-some-RI-checks.patch
Description: Binary data
v3-0001-Avoid-using-SPI-in-RI-trigger-functions.patch
Description: Binary data
