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Thread: Why different execution times for different instances for the same query?

Why different execution times for different instances for the same query?

From
Kishore B
Date:

Hi All,

 

I am Kishore doing freelance development of J2EE applications.

 

We switched to use Postgresql recently because of the advantages it has over other commercial databases. All went well untill recently, untill we began working on an application that needs to maintain  a huge database.

 

I am describing the problem we are facing below. Can you please take a look at the case, and help me in resolvign the issue.

 

We are executing a single query that returned very fast on the first instance. But when I executed the same query for multiple times, it is giving strange results. It is not coming back. 
 
When I checked with the processes running in the system, I observed that multiple instances of postmaster are running and all of them are consuming very high amounts of memory. I could also observe that they are sharing the memory in a uniform distribution across them.
 
Can you please let me know if you have experienced the same and how do you resolved it?
 
Thank you,
Kishore. 

Re: Why different execution times for different instances for the same query?

From
"Jim C. Nasby"
Date:
It's impossible to say without more information. What's the query that's
slow? What's EXPLAIN ANALYZE of that query show? How often are you
vacuuming? How often are you analyzing? What postgresql.conf options
have you changed from the defaults? What hardware is this running on?

The memory usage you're seeing is most likely just the OS reporting
shared memory as if it was being used by each backend, even though it's
just one set of memory that's shared between all the processes.

On Wed, Oct 26, 2005 at 01:48:16AM +0530, Kishore B wrote:
> Hi All,
>
>  I am Kishore doing freelance development of J2EE applications.
>
>  We switched to use Postgresql recently because of the advantages it has
> over other commercial databases. All went well untill recently, untill we
> began working on an application that needs to maintain a huge database.
>
>  I am describing the problem we are facing below. Can you please take a look
> at the case, and help me in resolvign the issue.
>
>  We are executing a single query that returned very fast on the first
> instance. But when I executed the same query for multiple times, it is
> giving strange results. It is not coming back.
>  When I checked with the processes running in the system, I observed that
> multiple instances of postmaster are running and all of them are consuming
> very high amounts of memory. I could also observe that they are sharing the
> memory in a uniform distribution across them.
>  Can you please let me know if you have experienced the same and how do you
> resolved it?
>  Thank you,
> Kishore.

--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461