Re: Grouped Index Tuples

Heikki Linnakangas wrote:
> Jim C. Nasby wrote:
> > On Thu, Dec 07, 2006 at 10:30:11AM +0000, Heikki Linnakangas wrote:
> >> I've cut a new version of the GIT patch I posted earlier, and collected
> >> all my dispersed todo-lists, post-it notes, performance results,
> >> supplementary patches etc. I had to a single web-page:
> >>
> >> http://community.enterprisedb.com/git/
> >>
> >> Perhaps the most interesting stuff apart from the patch itself is the
> >> performance results. I've run some CPU bound tests to measure the extra
> >> CPU overhead it causes. The CPU overhead is significant, the worst case
> >> being a select of a single row from a table with just one integer column.
> >>
> >> However, the I/O savings are also the greatest for that same test case,
> >> as the table grows and the test becomes I/O bound. I don't have the
> >> numbers now, but earlier runs showed that the duration of the test was
> >> roughly halved, which makes sense because the patch reduced the index
> >> size so that it fit in memory, reducing the number of physical I/Os
> >> required per select from 2 to 1.
> >>
> >> ISTM that if we want to enable GIT automatically, we need a way to
> >> either reduce the CPU overhead, or have a smart heuristic to tune the
> >> feature so that it's only enabled when it's beneficial.
> >
> > The maintain_cluster_order patch is useful by itself, and handles an
> > existing TODO regarding pulling pages out of WAL in a specified order to
> > maintain clustering.
>
> Pull pages out of WAL? That must be a typo...

I assume he meant FSM (free space map).

--
Bruce Momjian bruce(at)momjian(dot)us
EnterpriseDB http://www.enterprisedb.com

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