Re: HOT pgbench results

On Tue, 2007-08-07 at 20:27 +0100, Gregory Stark wrote:
> "Simon Riggs" <simon@2ndquadrant.com> writes:
> 
> > On Tue, 2007-08-07 at 13:16 +0100, Heikki Linnakangas wrote:
> >> I ran some CPU intensive pgbench tests on HOT. Results are not
> >> surprising, HOT makes practically no difference on the total transaction
> >> rate, but reduces the need to vacuum:
> >> ...
> > Nor would I expect anything else, on this test.
> 
> I think the surprising thing was that it wasn't slower due to the extra cpu
> spent pruning tuples.

...balanced by the extra time spent adding new blocks and doing
block-spanning updates without HOT.

For CPU bound situations, the real-world difference lies in the logical
I/O we avoid by not doing index insertions. Larger tables have deeper
index trees, so cause more block accesses to locate the block into which
to insert. Small tables with few indexes aren't a real test of that,
even if it does illustrate the basic CPU balance that HOT now offers in
its latest incarnation (well done Heikki and Pavan). 

--  Simon Riggs EnterpriseDB  http://www.enterprisedb.com