On 9/10/07, Simon Riggs <[EMAIL PROTECTED]> wrote: > > On Mon, 2007-09-10 at 12:17 +0100, Heikki Linnakangas wrote: > > Bruce Momjian wrote: > > > (Can someone time the access time for following a chain that fills an > > > entire page (the worst case) vs. having a single tuple on the page?) > > > > Here is some results, on my laptop. > > > HEAD HOT HOT-opt HOT-pruned > > seqscan 19.9 21.1 20.1 11.5 > > idxscan 27.8 31.4 30.4 13.7 > > > > > Comparing the idxscan columns, it looks like following the chain *is* > > more expensive than having to go through killed index pointers. Pruning > > clearly does help. > > > > Given that this test is pretty much the worst case scenario, I'm ok with > > not pruning for the purpose of keeping chains short. > > I wasn't expecting that result and had accepted the counter argument. > >
Yes, I go with Simon. I am also surprised that HOT-pruned did so well in this setup. I always thought that HOT would do well in update-intensive scenarios, but from the results it seems that HOT is also doing well for read-mostly queries. In this particular example, the first SELECT after the 250 UPDATEs would have pruned all the dead tuples and reduced HOT chain to a single tuple. Hence the total time for subsequent SELECTs improved tremendously. Thanks, Pavan -- Pavan Deolasee EnterpriseDB http://www.enterprisedb.com
