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Re: PostgreSQL clustering VS MySQL clustering

From: Kevin Brown <kevin(at)sysexperts(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: PostgreSQL clustering VS MySQL clustering
Date: 2005-01-28 20:46:10
Message-ID: 20050128204610.GB31166@filer (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
PFC wrote:
> So, here is something annoying with the current approach : Updating rows  
> in a table bloats ALL indices, not just those whose indexed values have  
> been actually updated. So if you have a table with many indexed fields and  
> you often update some obscure timestamp field, all the indices will bloat,  
> which will of course be corrected by VACUUM, but vacuum will have extra  
> work to do.

The MVCC approach probably doesn't leave you with many choices here.
The index entries point directly to the rows in the table, and since
an update creates a new row (it's the equivalent of doing an insert
then a delete), all indexes have to be updated to reflect the location
of the new row.

Unless my understanding of how this works is completely off...

Kevin Brown					      kevin(at)sysexperts(dot)com

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