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Re: selects from large tables

From: Rod Taylor <rbt(at)rbt(dot)ca>
To: Nikk Anderson <Nikk(dot)Anderson(at)parallel(dot)ltd(dot)uk>
Cc: "\"'Charles H(dot) \"Woloszynski'" <chw(at)clearmetrix(dot)com>,pgsql-performance(at)postgresql(dot)org
Subject: Re: selects from large tables
Date: 2002-11-20 15:31:05
Message-ID: 1037806265.87360.18.camel@jester (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, 2002-11-20 at 10:08, Nikk Anderson wrote:
> Hi, 
> 
> I tried a test cluster on a copy of our real data - all 10 million
> rows or so.  WOW!   The normal select performance improved
> drastically.  
> 
> Selecting 3 months worth of data was taking 146 seconds to retrieve. 
> After clustering it took 7.7 seconds!  We are now looking into ways we
> can automate clustering to keep the table up to date.  The cluster
> itself took around 2.5 hours.
> 
> As our backend systems are writing hundreds of rows of data in per
> minute into the table that needs clustering - will cluster handle
> locking the tables when dropping the old, and renaming the clustered
> data?  What happens to the data being added to the table while cluster
> is running? Our backend systems may have some problems if the table
> does not exist when it tries to insert, and we don't want to lose any
> data.

The table will be locked while cluster is running.  Meaning, any new
data will have to sit and wait.

Cluster won't buy much on a mostly clustered table.  But it's probably
worth it for you to do it when 20% of the tuples turnover (deleted,
updated, inserts, etc).


I'm a little curious to know when the last time you had run a VACUUM
FULL on that table was.

-- 
Rod Taylor <rbt(at)rbt(dot)ca>


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