Re: Indexing columns with low cardinality: persistent bitmap indexes?

Jaime-

Porque no utiliza Bitmap?

*Saludos Cordiales desde EEUU*
Martin
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> Date: Mon, 12 Jan 2009 16:20:40 -0500
> From: jcasanov(at)systemguards(dot)com(dot)ec
> To: regmeplease(at)gmail(dot)com
> Subject: Re: [GENERAL] Indexing columns with low cardinality: persistent bitmap indexes?
> CC: pgsql-general(at)postgresql(dot)org; bruno(dot)lavoie(at)gmail(dot)com
>
> On Mon, Jan 12, 2009 at 4:16 PM, Reg Me Please <regmeplease(at)gmail(dot)com> wrote:
> > On Monday 12 January 2009 21:38:02 Bruno Lavoie wrote:
> >> Hello,
> >>
> >> I have a column with a small number of distinct values, indexing this
> >> one with a standard BTree is useless. How do I can index this column
> >> efficiently? I searched and it seems that pg doesn't support the
> >> creation of persistent bitmap indexes... Is that feature planned in next
> >> releases of pg?
> >>
> >> Thanks
> >> Bruno Lavoie
> >
> > I would try partial indexes, as many as the distinct values.
> > I'm not sure this would help, though.
> >
>
> you should create partial indexes only on those values that are a
> lower fraction on the table
> ie: if you have
>
> value "fraction of the table that has this value"
> 1 5%
> 2 3%
> 3 20%
> 4 25%
> 5 47%
>
> then only partial indexes on values 1 and 2 are of some value
>
> --
> Atentamente,
> Jaime Casanova
> Soporte y capacitación de PostgreSQL
> Asesoría y desarrollo de sistemas
> Guayaquil - Ecuador
> Cel. +59387171157
>
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