Thread: Testing query times

Hi,

The first time I use a query its much slower than the second, third
etc. I want to do some testing with the 1st (slower) time. The only
way I have found to reproduce that slow time is to restart my
computer which is a huge pain. Is there a better way to clear
whatever Postgres is holding to make them faster. I have tried
restarting the Postgres service but that doesn't help.

Christine Penner
Ingenious Software
250-352-9495
christine@ingenioussoftware.com

On Thu, Dec 3, 2009 at 2:55 PM, Christine Penner
<christine@ingenioussoftware.com> wrote:
> Hi,
>
> The first time I use a query its much slower than the second, third etc. I
> want to do some testing with the 1st (slower) time. The only way I have
> found to reproduce that slow time is to restart my computer which is a huge
> pain. Is there a better way to clear whatever Postgres is holding to make
> them faster. I have tried restarting the Postgres service but that doesn't
> help.

Restarting pgsql accomplishes the same thing as regards pgsql.  BUT
most OSes also cache, so you need a way to flush the kernel / file
system cache.  That depends on which OS you're running.

Scott Marlowe wrote:

Restarting pgsql accomplishes the same thing as regards pgsql.  BUT
most OSes also cache, so you need a way to flush the kernel / file
system cache.  That depends on which OS you're running. 

Can't tell if this is Linux or Windows from how the question was asked.  Here's how to clear the OS cache on Linux: 

sync; echo 3 > /proc/sys/vm/drop_caches

And on Windows you should be able to clear it with CacheSet:  http://technet.microsoft.com/en-us/sysinternals/bb897561.aspx

-- 
Greg Smith    2ndQuadrant   Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com  www.2ndQuadrant.com