Robert Haas wrote: > On Fri, Jul 31, 2015 at 3:45 PM, Alvaro Herrera > <alvhe...@2ndquadrant.com> wrote:
> > I think the only way to close this hole is to have summarize_range() > > sleep until all open snapshots are gone after inserting the placeholder > > tuple and before acquiring the snapshot, similarly to how CREATE INDEX > > CONCURRENTLY does it. > > That's gonna be really slow, though, right? Even if you rework things > so that vacuum inserts all the placeholder tuples first, then waits, > then does all the summarization, that could easily turn a vacuum that > would have finished in a second into one that instead takes multiple > hours. During that time an AV worker is pinned down, and all sorts of > badness can ensue. Yeah, it is bad and I was concerned about that too. Thankfully I found another way to solve it, which is to forgo usage of MVCC here and instead use SnapshotAny. There's already a mode in IndexBuildHeapRangeScan that uses SnapshotAny, but it needs some tweaks to do what we need. I'm going to propose a patch along those lines shortly. > Maybe I'm misunderstanding, but this whole thing seems like a pretty > serious problem for BRIN. :-( With this new approach it shouldn't be. -- 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
