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Re: bitmap indexes - performance

From: Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: bitmap indexes - performance
Date: 2010-07-02 08:30:09
Message-ID: 4C2DA391.5010502@catalyst.net.nz (view raw or flat)
Thread:
Lists: pgsql-hackers
On 02/07/10 13:31, Bruce Momjian wrote:
> Leonardo F wrote:
>    
>> I'm trying to find more docs that explain the "improvements" of
>> bitmap indexes in other products... but most of what I've found
>> talks about bitmapAND/OR.... which is something that is very
>> cool, but that postgres already does even with btree indexes...
>> or index creation time/size, which are, for the moment, the only
>> things that I'm pretty confident the patch would actually provide.
>>      
> I think a real limitation of on-disk bitmap indexes is that they are
> only feable for low cardinality columns, while btree handles all column
> types.
>
>    

I recall that for (some/most? of) those low cardinality cases, (on disk) 
bitmap indexes would perform better too. I think the size saving alone 
is a huge win for serious data warehousing situations. On the other hand 
problems I recall are possibly reduced UPDATE/DELETE performance and 
issues with CREATE INDEX CONCURRENTLY and also complications with VACUUM 
(altho these last two may have been sorted - I've lost touch with what 
was in the most recent patches).

regards

Mark

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