Thread: SELECT performance problem

SELECT performance problem

From

Glenn Sullivan

Date:

20 February 2007, 22:35:32

I am updating from 7.4.5 to 8.2.3.  I have noticed a significant
slowdown in simple searches such as
     "select filename from vnmr_data where seqfil = 'sems';"
This returns 12 rows out of 1 million items in the table.
On 7.4.5, this takes about 1.5 seconds.  On 8.2.3, it is taking
about 9 seconds.

I have played with different values of:
work_mem, temp_buffers, shared_buffers and effective_cache_size
and none of them make any difference.

I am running on redhat Linux 4   64bit.

Any ideas?

Glenn

Re: SELECT performance problem

From

Jeff Frost

Date:

20 February 2007, 22:41:52

On Tue, 20 Feb 2007, Glenn Sullivan wrote:

> I am updating from 7.4.5 to 8.2.3.  I have noticed a significant
> slowdown in simple searches such as
>    "select filename from vnmr_data where seqfil = 'sems';"
> This returns 12 rows out of 1 million items in the table.
> On 7.4.5, this takes about 1.5 seconds.  On 8.2.3, it is taking
> about 9 seconds.
>
> I have played with different values of:
> work_mem, temp_buffers, shared_buffers and effective_cache_size
> and none of them make any difference.
>
> I am running on redhat Linux 4   64bit.

Glenn,

Can you forward us the explain analyze output from 7.4.5 and 8.2.3 for the
query in question?

Also, is the hardware the same between 7.4.5 and 8.2.3?  If not, what is the
difference?

--
Jeff Frost, Owner     <jeff@frostconsultingllc.com>
Frost Consulting, LLC     http://www.frostconsultingllc.com/
Phone: 650-780-7908    FAX: 650-649-1954

Re: SELECT performance problem

From

"Dave Dutcher"

Date:

20 February 2007, 22:47:05

Did you run ANALYZE on your data after importing it into 8.2.3?  Is there an
index on the seqfil column?  If so, you should post the output of EXPLAIN
ANALYZE from both systems if possible.


> -----Original Message-----
> From: pgsql-performance-owner@postgresql.org
> [mailto:pgsql-performance-owner@postgresql.org] On Behalf Of
> Glenn Sullivan
> Sent: Tuesday, February 20, 2007 5:22 PM
> To: pgsql-performance@postgresql.org
> Subject: [PERFORM] SELECT performance problem
>
>
> I am updating from 7.4.5 to 8.2.3.  I have noticed a significant
> slowdown in simple searches such as
>      "select filename from vnmr_data where seqfil = 'sems';"
> This returns 12 rows out of 1 million items in the table.
> On 7.4.5, this takes about 1.5 seconds.  On 8.2.3, it is taking
> about 9 seconds.
>
> I have played with different values of:
> work_mem, temp_buffers, shared_buffers and effective_cache_size
> and none of them make any difference.
>
> I am running on redhat Linux 4   64bit.
>
> Any ideas?
>
> Glenn
>
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