Re: SSI patch version 8

Kevin Grittner <kevin.grittner@wicourts.gov>

From: "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
To: "Heikki Linnakangas" <heikki.linnakangas@enterprisedb.com>
Cc: "Dan Ports" <drkp@csail.mit.edu>, "john.okite@gmail.org" <john.okite@gmail.org>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, <anssi.kaariainen@thl.fi>
Date: 2011-01-13T15:02:12Z
Lists: pgsql-hackers
Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> wrote:
 
> where exactly is the extra overhead coming from?
 
Keep in mind that this is a sort of worst case scenario.  The data
is fully cached in shared memory and we're doing a sequential pass
just counting the rows.  In an earlier benchmark (which I should
re-do after all this refactoring), random access queries against a
fully cached data set only increased run time by 1.8%.  Throw some
disk access into the mix, and the overhead is likely to get lost in
the noise.
 
But, as I said, count(*) seems to be the first thing many people try
as a benchmark, and this is a symptom of a more general issue, so
I'd like to find a good solution.
 
-Kevin