Re: performance impact of index
From: Bricklen <Xbricklen_at_yahoo.comX>
Date: Mon, 24 May 2004 17:47:34 GMT
Message-ID: <Wyqsc.575006$oR5.410422_at_pd7tw3no>
> I your schema is purely read-only, you can create as much indexes as you
> want. But bitmapped indexes are only useful when the cardinality is
> relatively low (about 1.000 distinct values max).
> In other cases (more than one thousand distinct values for the column),
> it can be better to use b-tree indexes, but don't forget that the
> storage needed is much bigger.
> You can alos deal with function-based indexes if you want.
> .
Date: Mon, 24 May 2004 17:47:34 GMT
Message-ID: <Wyqsc.575006$oR5.410422_at_pd7tw3no>
mrFarenheit wrote:
>>
> I your schema is purely read-only, you can create as much indexes as you
> want. But bitmapped indexes are only useful when the cardinality is
> relatively low (about 1.000 distinct values max).
> In other cases (more than one thousand distinct values for the column),
> it can be better to use b-tree indexes, but don't forget that the
> storage needed is much bigger.
> You can alos deal with function-based indexes if you want.
> .
[Quoted] Would you mind proving your statement "bitmapped indexes are only useful when the cardinality is relatively low (about 1.000 distinct values max)"?
I'd be interested to see how you came up with that number, and the ratios you've used for it. Received on Mon May 24 2004 - 19:47:34 CEST