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Re: strange performance regression between 7.4 and 8.1



I would just like to note here that this is an example of inefficient strategy.

We could all agree (up to a certain economical point) that Alex saved the most expensive one thousand dollars of his life.

I don't know the financial status nor the size of your organization, but I'm sure that you have selected the path that has cost you more.

In the future, an investment on memory for a (let's say) rather small database should be your first attempt.

Yours,
Rodrigo Madera

On 3/6/07, Alex Deucher <alexdeucher@xxxxxxxxx> wrote:
On 3/6/07, Ron <rjpeace@xxxxxxxxxxxxx> wrote:
> At 10:25 AM 3/6/2007, Alex Deucher wrote:
> >On 3/5/07, Guido Neitzer < lists@xxxxxxxxxxx> wrote:
> >>On 05.03.2007, at 19:56, Alex Deucher wrote:
> >>
> >> > Yes, I started setting that up this afternoon.  I'm going to test that
> >> > tomorrow and post the results.
> >>
> >>Good - that may or may not give some insight in the actual
> >>bottleneck. You never know but it seems to be one of the easiest to
> >>find out ...
> >
> >Well, the SAN appears to be the limiting factor.  I set up the DB on
> >the local scsi discs (software RAID 1) and performance is excellent
> >(better than the old server).  Thanks for everyone's help.
> >
> >Alex
>
> What kind of SAN is it and how many + what kind of HDs are in it?
> Assuming the answers are reasonable...
>

It's a Hitachi WMS/Tagmastore.  105 hitachi SATA drives; 4 Gbps FC.

> Profile the table IO pattern your workload generates and start
> allocating RAID sets to tables or groups of tables based on IO pattern.
>
> For any table or group of tables that has a significant level of
> write IO, say >= ~25% of the IO mix, try RAID 5 or 6 first, but be
> prepared to go RAID 10 if performance is not acceptable.
>

Right now it's designed for max capacity: big RAID 5 groups.  I expect
I'll probably need RAID 10 for decent performance.

> Don't believe any of the standard "lore" regarding what tables to put
> where or what tables to give dedicated spindles to.
> Profile, benchmark, and only then start allocating dedicated resources.
> For instance, I've seen situations where putting pg_xlog on its own
> spindles was !not! the right thing to do.
>

Right.  Thanks for the advice.  I'll post my results when I get around
to testing some new SAN configurations.

Alex

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