On the test box this seems to have completely resolved our problem.
I'll be scheduling an upgrade on the production cluster to verify it.
Thanks
On Thu, Sep 13, 2012 at 11:08 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Mike Roest <mike.roest@replicon.com> writes: > We have a interesting thing happening on one of our DB's that when > autovacuum runs against the pg_catalog tables (or we run a manual vacuum) > we get a large delay in opening new connections.
I think you're hitting the problem that was fixed here:
Prevent synchronized scanning when systable_beginscan chooses a heapscan.
The only interesting-for-performance case wherein we force heapscan here is when we're rebuilding the relcache init file, and the only such case that is likely to be examining a catalog big enough to be syncscanned is RelationBuildTupleDesc. But the early-exit optimization in that code gets broken if we start the scan at a random place within the catalog, so that allowing syncscan is actually a big deoptimization if pg_attribute is large (at least for the normal case where the rows for core system catalogs have never been changed since initdb). Hence, prevent syncscan here. Per my testing pursuant to complaints from Jeff Frost and Greg Sabino Mullane, though neither of them seem to have actually hit this specific problem.
Back-patch to 8.3, where syncscan was introduced.
> For our setup we're running postgres 9.1.1 compiled from source on Centos > 5.8 x64 (Dual Xeon x5650 with 32 gigs of ram)
