> 1. create table test (id int4, aaa int4, primary key (id));
> 2. insert into test values (0,1);
> 3. Execute "update test set aaa=1 where id=0;" in an endless loop
>
> I just did the test on PostgreSQL 7.4.12 and MySQL 5.0.22 (MyISAM,
> sorry had no configured InnoDB). Ubuntu 6.0.6, AMD64, 2GB, default
> database settings.
>
> MySQL performs very well, approximately 15000-20000 updates per second
> with no degradation of performance.
>
> PostgreSQL does approximately 1600 records per second for the first
> 10000, then 200rps for the first 100k records, and then slower and
> slower downgrading to 10-20 rps(!!!) when reaching 300k.
Something is wrong with your test code. If I had to guess I would say
you did all the updates in a single transaction without committing
them, in which case yes it will slow down until you commit.