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Re: Reducing stats collection overhead

From: Arjen van der Meijden <acm(at)tweakers(dot)net>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Reducing stats collection overhead
Date: 2007-07-31 05:16:10
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Lists: pgsql-hackers
On 31-7-2007 5:07 Alvaro Herrera wrote:
> Arjen van der Meijden wrote:
>> Afaik Tom hadn't finished his patch when I was testing things, so I don't 
>> know. But we're in the process of benchmarking a new system (dual quad-core 
>> Xeon) and we'll have a look at how it performs in the postgres 8.2dev we 
>> used before, the stable 8.2.4 and a fresh HEAD-checkout (which we'll call 
>> 8.3dev). I'll let you guys (or at least Tom) know how they compare in our 
>> benchmark.
> So, ahem, did it work? :-)

The machine turned out to have a faulty mainboard, so we had to 
concentrate on first figuring out why it was unstable and then whether 
the replacement mainboard did make it stable in a long durability 
test.... Of course that behaviour only appeared with mysql and not with 
postgresql, so we had to run our mysql-version of the benchmark a few 
hundred times, rather than testing various versions, untill the machine 
had to go in production.

So we haven't tested postgresql 8.3dev on that machine, sorry.

Best regards,


>> On 18-5-2007 15:12 Alvaro Herrera wrote:
>>> Tom Lane wrote:
>>>> Arjen van der Meijden told me that according to the
>>>> benchmark, HEAD is noticeably slower than 8.2.4, and I soon confirmed
>>>> here that for small SELECT queries issued as separate transactions,
>>>> there's a significant difference.  I think much of the difference stems
>>>> from the fact that we now have stats_row_level ON by default, and so
>>>> every transaction sends a stats message that wasn't there by default
>>>> in 8.2.  When you're doing a few thousand transactions per second
>>>> (not hard for small read-only queries) that adds up.
>>> So, did this patch make the performance problem go away?

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