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Re: Postgresql 8.0 beta 1 - strange cpu usage statistics and slow

From: Gaetano Mendola <mendola(at)bigfoot(dot)com>
To: Shelby Cain <alyandon(at)yahoo(dot)com>
Subject: Re: Postgresql 8.0 beta 1 - strange cpu usage statistics and slow
Date: 2004-08-19 20:57:58
Message-ID: 41251456.1030906@bigfoot.com (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers-win32
Shelby Cain wrote:

> I'm putting 8.0 through its paces and here are a few
> things I've noticed on the native win32 port running
> on my workstation (2.0g p4 w/256 megs of ram).
> 
> Here is the output of "vacuum verbose item":
> 
> ====================
> INFO:  vacuuming "public.item"
> INFO:  "item": removed 246381 row versions in 24044
> pages
> DETAIL:  CPU -1.-1612s/-1.99u sec elapsed 1434.79 sec.
> INFO:  "item": found 246381 removable, 492935
> nonremovable row versions in 50413 pages
> DETAIL:  0 dead row versions cannot be removed yet.
> There were 100991 unused item pointers.
> 0 pages are entirely empty.
> CPU 1081264882.-821s/0.02u sec elapsed 1682.87 sec.
> 
> Query returned successfully with no result in 1683460
> ms.
> ====================
> 
> As you can see the cpu statistics are obviously bogus
> although the elasped time is correct.
> 
> My other concern is the length of time that vacuum
> runs when cost based vacuuming is disabled.
> 
> Under 8.0, if I run an update statement (update item
> where set cost = cost + 0 where country = 'US' [causes
> an update w/o really changing data]) that updates half
> the rows in the table (~250k out of 500k - average
> tuple width is about 500 bytes) and then execute a
> regular vacuum it takes approximately 1400 seconds to
> complete.  A vacuum full performed immediately after
> takes on the order of 2000 seconds to complete.  

On Windows XP with 8.0beta1 I'm experiencing different
values instead, after updating 800K rows the plain vacuum
takes 200 seconds and the vacuum full immediately after
takes 620 seconds.

In both case the cpu usage was near zero.
I'm using a 2.2GHZ 1GB di RAM and I'm using 64MB to workmem.



Regards
Gaetano Mendola







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