Re: Large table performance

Mark,

This behavior likely depends on how the data is loaded into the DBMS. If
the records you are fetching are distributed widely among the 3M records on
disk, then

On 1/12/07 4:31 PM, "Mark Dobbrow" <mdobbrow(at)yahoo(dot)com> wrote:

> Hello -
>
> I have a fairly large table (3 million records), and am fetching 10,000
> non-contigous records doing a simple select on an indexed column ie
>
> select grades from large_table where teacher_id = X
>
> This is a test database, so the number of records is always 10,000 and i have
> 300 different teacher ids.
>
> The problem is, sometimes fetching un-cached records takes 0.5 secs and
> sometimes (more often) is takes more like 10.0 seconds
>
> (fetching the same records for a given teacher_id a second time takes about
> 0.25 secs)
>
> Has anyone seen similar behavior or know what the solution might be?
>
> any help much appreciated,
> Mark
>
>
>
> ps. My shared_buffers is set at 5000 (kernal max), and work_mem=8192
>
>
>