On Fri, Nov 18, 2005 at 02:56:52PM -0500, Gregory Maxwell wrote: > However, some great ideas have been proposed here which would not only > help in that case but would otherwise be quite useful. > > *Inclusion of a 'MVCC inflight' bit in indexes which would allow > skipping MVCC checks in clumps of an index scan which have no pending > changes. This would further close the performance gap between PG and > non-MVCC databases for some workloads. > *Introduction of high performance table sampling, which would be > useful in many applications (including counting where there is a where > clause) as well as for testing and adhoc queries. > and > *a estimate_count() that provides the planner estimate, which would > return right away and provide what is really needed most of the time > people try to count(*) on a large table.
What about Greg Stark's idea of combining Simon's idea of storing per-heap-block xmin/xmax with using that information in an index scan? ISTM that's the best of everything that's been presented: it allows for faster index scans without adding a lot of visibility overhead to the index heap, and it also allows VACUUM to hit only pages that need vacuuming. Presumably this could also be used as the on-disk backing for the FSM, or it could potentially replace the FSM. -- Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED] Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
