On 27 Srpen 2011, 6:01, Noah Misch wrote:
> On Fri, Aug 26, 2011 at 10:46:33AM +0200, Tomas Vondra wrote:
>> 1. collect pg_stat_bgwriter stats
>> 2. run pgbench for 10 minutes
>> 3. collect pg_stat_bgwriter stats (to compute difference with (1))
>> 4. kill the postmaster
>>
>> The problem is that when checkpoint stats are collected, there might be
>> a
>> checkpoint in progress and in that case the stats are incomplete. In
>> some
>> cases (especially with very small db blocks) this has significant impact
>> because the checkpoints are less frequent.
>
> Could you remove this hazard by adding a step "2a. psql -c CHECKPOINT"?
I already do that, but it really does not solve the issue. It just aligns
the first expected 'timed' checkpoint, it does not solve the problem with
in-progress checkpoints unless the runs behave exactly the same (and
that's the boring case).
Tomas