Message-ID: <46E05E4D.3010003@p-dw.com>
Date: Thu, 06 Sep 2007 22:08:45 +0200
From: Patric <lists@p-dw.com>
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To: pgsql-performance@postgresql.org
Subject: Reasonable amount of indices
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Hi,
    I've a question about amount of indices.
   
    I explain my issue based on an example:
    Table which contains person information, one row per person.
    There will be lots of SELECTS doing search by special criteria, 
e.g.: Age, Gender.

    Now there will be 4 User groups which will select on the table:
    Group 1) Always doing reads on specific continents.
    Group 2) Always doing reads in specific country.
    Group 3) Always doing reads in specific region within a country.
    Group 4) Always doing reads in specific city.

    I 'm indexing the the important attributes. Would be about 5 to 6 
independent indexes.
    As there will be millions of rows, quite a lot of hits will be 
returned, I guess
    it will generate big bitmaps to calculate the intersection of the 
indices.

    Ok to prevent this from happening I'd wanted to create 4 Indexes per 
attribute, with
    special predicate, so users which only query for a country don't 
scan an index
    which indexed the entire globe:

    e.g ..
    CREATE index BlaBla_city on table tblusers(dtage) WHERE dtcity='London';
    CREATE index BlaBla_country on table tblusers(dtage) WHERE 
dtcountry='uk';
    CREATE index BlaBla_continent on table tblusers(dtage) WHERE 
dtcontinent='europe';
    etc.

    SELECT * FROM tblusers WHERE dtcontinent='europe' and age='23'
    would then postgres lead to use the special index made for europe.

    Now that I've 4 Indexes. an Insert or update will lead to some more 
overhead,  but which would be ok.

    My Question now is: Is it wise to do so, and create hundreds or 
maybe thousands of Indices
    which partition the table for the selections.

    Does postgres scale good on the selecton of indices or is the 
predicate for indices not
    layed out for such a usage?

    (PS: Don't want partition with method postgres offers..)

thanks in advance,
patric