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Re: Seq scans status update

From: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Seq scans status update
Date: 2007-05-22 15:06:11
Message-ID: 465306E3.60902@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-patches
Not yet, there's still one issue that needs fixing.

Bruce Momjian wrote:
> Great.  Based on this, do you have a patch that is ready to apply.
> 
> ---------------------------------------------------------------------------
> 
> Heikki Linnakangas wrote:
>> Heikki Linnakangas wrote:
>>> In any case, I'd like to see more test results before we make a 
>>> decision. I'm running tests with DBT-2 and a seq scan running in the 
>>> background to see if the cache-spoiling effect shows up. I'm also trying 
>>> to get hold of some bigger hardware to run on. Running these tests takes 
>>> some calendar time, but the hard work has already been done. I'm going 
>>> to start reviewing Jeff's synchronized scans patch now.
>> Here are the results of the DBT-2 tests:
>>
>> http://community.enterprisedb.com/seqscan/imola/
>>
>> In each of these tests, at the end of rampup a script is started that 
>> issues a "SELECT COUNT(*) FROM stock" in a loop, with 2 minute delay 
>> between end of previous query and start of next one.
>>
>> The patch makes the seq scans go significantly faster. In the 1 hour 
>> test period, the patched tests perform roughly 30-100% as many selects 
>> as unpatched tests.
>>
>> With 100 and 105 warehouses, it also significantly reduces the impact of 
>> the seq scan on other queries; response times are lower with the patch. 
>> With 120 warehouses the reduction of impact is not as clear, but when 
>> you plot the response times it's still there (the plots on the "response 
>> times charts"-page are useless because they're overwhelmed by the 
>> checkpoint spike).
>>
>> -- 
>>    Heikki Linnakangas
>>    EnterpriseDB   http://www.enterprisedb.com
>>
>> ---------------------------(end of broadcast)---------------------------
>> TIP 5: don't forget to increase your free space map settings
> 


-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

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