Noah Misch <n...@leadboat.com> writes: > On Mon, Dec 19, 2011 at 12:05:09PM -0500, Robert Haas wrote: >> Yet another option, which I wonder whether we're dismissing too >> lightly, is to just call GetSnapshotData() and do the scan using a >> plain old MVCC snapshot. Sure, it's more expensive than SnapshotNow, >> but is it expensive enough to worry about?
That might actually be workable ... > I created a function that does this in a loop: > HeapTuple t; > CatalogCacheFlushCatalog(ProcedureRelationId); > t = SearchSysCache1(PROCOID, ObjectIdGetDatum(42) /* int4in */); > if (!HeapTupleIsValid(t)) > elog(ERROR, "cache lookup failed for function 42"); > ReleaseSysCache(t); ... but this performance test seems to me to be entirely misguided, because it's testing a situation that isn't going to occur much in the field, precisely because the syscache should prevent constant reloads of the same syscache entry. Poking around a bit, it looks to me like one of the bigger users of non-cache-fronted SnapshotNow scans is dependency.c. So maybe testing the speed of large cascaded drops would be a more relevant test case. For instance, create a schema containing a few thousand functions, and see how long it takes to drop the schema. Another thing that would be useful to know is what effect such a change would have on the time to run the regression tests with CLOBBER_CACHE_ALWAYS. That has nothing to do with any real-world performance concerns, but it would be good to see if we're going to cause a problem for the long-suffering buildfarm member that does that. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers