Re: Is Vacuum/analyze destroying my performance?

Carlo Stonebanks wrote:
>> Just a wild guess, but the performance problem sounds like maybe as your
>> data changes, eventually the planner moves some query from an index scan
>> to a sequential scan, do you have any details on what queries are taking
>> so long when things are running slow?  You can turn on the GUC var
>> "log_min_duration_statement" and see what queries are slow and then
>> manually check them with an explain analyze, that might help.
>>
> This is pretty well what I think is happening - I expect all queries to
> eventually move from seq scans to index scans. I actually have a SQL logging
> opion built into the import app.
>
> I just can't figure out how the planner can be so wrong. We are running a 4
> CPU server (two dual core 3.2 GHz Xeons) with 4GB RAM and Windows Server
> 2003 x64 and a PERC RAID subsystem (I don't know the RAID type). I know that
> the metrics for the planner can be changed - is the default config for
> postgesql not suitable for our setup? For this server, we would like to be
> optimised for high speed over a few connections, rather than the classic
> balanced speed over many connections.

If it is the planner choosing a very bad plan, then I don't think your
hardware has anything to do with it.  And, we can't diagnose why the
planner is doing what it's doing without a lot more detail.  I suggest
you do something to figure out what queries are taking so long, then
send us an explain analyze, that might shine some light on the subject.