Re: Sustained inserts per sec ... ?

On Tue, 2005-04-05 at 18:55 -0400, Christopher Petrilli wrote:
> On Apr 5, 2005 3:48 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > B-trees aren't unique to PostgreSQL; the explanation developed here
> > would work equally well for any database system that used tree-based
> > indexes. Do we still think that MySQL can do this when PostgreSQL
> > cannot? How?
> >
> > Do we have performance test results showing the same application load
> > without the degradation? We don't need to look at the source code to
> > measure MySQL performance...
>
> http://www.amber.org/~petrilli/diagrams/comparison_mysql_pgsql.png
>
> That chart shows MySQL (using INSERT against MyISAM tables) and
> PostgreSQL (using COPY) running with the exact same code otherwise.
> Note that MySQL does hit a bit of a wall, but nothing as drastic as
> PostgreSQL and actually maintains something "more flat". The red and
> blue dashed lines are the 95th percentile point.

Interesting comparison. Any chance of separating the graphs as well, I'm
interested in the detail on both graphs.

Could you estimate the apparent periodicity on the PostgreSQL graphs?

> My suspicion is that what we're seeing is WAL issues, not particularly
> index issues. The indices just fill up the WAL faster because there's
> more data. This is a wag basically, but it would seem to explain the
> difference. In both cases, the indices were identical. Five on each.

Let's test the shared_buffers theory.

Would you mind loading only 5M rows per table, but load the same amount
of data overall? That should keep us within the comparable zone overall.

Best Regards, Simon Riggs