Re: Sustained inserts per sec ... ?

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.

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.

One interesting thing... PostgreSQL starts out a good bit faster, but
looses in the end.

Chris
--
| Christopher Petrilli
| petrilli(at)gmail(dot)com