Re: Performance Tuning and Disk Cache

[David Boreham <david_list@xxxxxxxxxxx>]

Barry Moore wrote:

> I have a very slow query that I'm trying to tune.  I think my  
> performance tuning is being complicated by the system's page cache.
>
> If a run the query after the system has been busy with other tasks  
> for quite a long time then the query can take up to 8-10 minutes to  
> complete.  If I then rerun the same query it will complete in a  
> couple of seconds.
>
> Does anyone know how I can repeatedly run the same query in the  
> "worst case scenario" of no postgres data in the disk cache (e.g.,  
> clear the page cache or force it to be ignored)?

In my experience the only 100% reliable way to do this is to reboot the 
machine.