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Re: Bitmap indexes

From: PFC <lists(at)boutiquenumerique(dot)com>
To: "PostgreSQL Perfomance" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Bitmap indexes
Date: 2005-01-28 17:14:14
Message-ID: opslbot0keth1vuj@musicbox (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
> There's a great deal about this in the list archives (probably more in
> pgsql-hackers than in -performance).  Most of the current interest has
> to do with building in-memory bitmaps on the fly, as a way of decoupling
> index and heap scan processing.  Which is not quite what you're talking
> about but should be pretty effective for low-cardinality cases.  In
> particular it'd allow AND and OR combination of multiple indexes, which
> we do poorly or not at all at the moment.

	Is this called a star join ?

	It would also allow to access the data pages in a more sequential order  
if the rows are not required to be retrieved in index order, which would  
potentially be a large speedup for index scans concerning more than the  
usual very small percentage of rows in a table : if several rows to be  
retrieved are on the same page, it would visit this page only once.

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