Re: how to (temporarily) disable/minimize benefits of disk block cache or postgresql shared buffer

On 01/07/10 17:41, Rajesh Kumar Mallah wrote:
> Hi,
>
> this is not really a performance question , sorry if its bit irrelevant
> to be posted here. We have a development environment and we want
> to optimize the non-database parts of the application. The problem is
> that subsequent run of queries are execute very fast and makes the
> performance analysis a trivial problem. We want that the subsequent runs
> of query should take similar times as the first run so that we can work
> on the optimizing the calling patterns to the database.

You can get rid of PostgreSQL's caches in shared_buffers by restarting
the PostgreSQL server. I don't know if there's any more convenient way.
Alternately, just set a really minimal shared_buffers that's just enough
for your connections so there's not much room for cached data.

If you are running a Linux server (as you didn't mention what you're
running on) you can drop the OS disk cache quite easily:

http://linux-mm.org/Drop_Caches
http://www.linuxinsight.com/proc_sys_vm_drop_caches.html

AFAIK for most other platforms you have to use a tool that gobbles
memory to force caches out. On Windows, most of those garbage tools that
claim to "free" memory do this - it's about the only time you'd ever
want to use one, since they do such horrid things to performance.

--
Craig Ringer