Re: testing HS/SR - 1 vs 2 performance

Hi Simon,

In another thread you mentioned you were lacking information from me:

On Tue, May 4, 2010 17:10, Simon Riggs wrote:
>
> There is no evidence that Erik's strange performance has anything to do
> with HS; it hasn't been seen elsewhere and he didn't respond to
> questions about the test setup to provide background. The profile didn't
> fit any software problem I can see.
>

I'm sorry if I missed requests for things that where not already mentioned.

Let me repeat: OS: Centos 5.4 2 quadcores: Intel(R) Xeon(R) CPU X5482 @ 3.20GHz Areca 1280ML primary and standby db
bothon a 12 disk array (sata 7200rpm, Seagat Barracuda ES.2)
 

It goes without saying (I hope) that apart from the pgbench tests
and a few ssh sessions (myself), the machine was idle.

It would be interesting if anyone repeated these simple tests and produced
evidence that these non-HS.

(Unfortunately, I have at the moment not much time for more testing)


thanks,

Erik Rijkers



On Sun, April 25, 2010 21:07, Simon Riggs wrote:
> On Sun, 2010-04-25 at 20:25 +0200, Erik Rijkers wrote:
>
>> Sorry if it's too much data, but to me at least it was illuminating;
>> I now understand the effects of the different parameters better.
>
> That's great, many thanks.
>
> A few observations
>
> * Standby performance is actually slightly above normal running. This is
> credible because of the way snapshots are now taken. We don't need to
> scan the procarray looking for write transactions, since we know
> everything is read only. So we scan just the knownassignedxids, which if
> no activity from primary will be zero-length, so snapshots will actually
> get taken much faster in this case on standby. The snapshot performance
> on standby is O(n) where n is the number of write transactions
> "currently" on primary (transfer delays blur the word "currently").
>
> * The results for scale factor < 100 are fine, and the results for >100
> with few connections get thrown out by long transaction times. With
> larger numbers of connections the wait problems seem to go away. Looks
> like Erik (and possibly Hot Standby in general) has an I/O problem,
> though "from what" is not yet determined. It could be just hardware, or
> might be hardware plus other factors.
>
> --
>  Simon Riggs           www.2ndQuadrant.com
>
>