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Index not used on group by

From: Andrey Repko <repko(at)sart(dot)must-ipra(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Index not used on group by
Date: 2005-09-27 09:14:31
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Hello all,

    I have table ma_data, that contain above 300000 rows.
   This table has primary key id, and field alias_id.
   I create index (btree)on this field.
   Set statistic:

 ALTER TABLE "public"."ma_data"

   So, when I do something like
     SELECT alias_id FROM ma_data GROUP BY alias_id
   and have (with seq_scan off):
   Group  (cost=0.00..1140280.63 rows=32 width=4) (actual time=0.159..2640.090 rows=32 loops=1)
      ->  Index Scan using reference_9_fk on ma_data  (cost=0.00..1139526.57 rows=301624 width=4) (actual time=0.120..1471.128 rows=301624 loops=1)
    Total runtime: 2640.407 ms
   (3 rows)

   As I understand there are some problems with visibility of records,
   but some others DBMS used indexes without problems(for example
   FireBird)? Or maybe some another information be helpful for me and

С наилучшими пожеланиями,
  Репко Андрей Владимирович       mailto:repko(at)sart(dot)must-ipra(dot)com


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Next:From: Ahmad FajarDate: 2005-09-27 09:39:55
Subject: Re: Query seem to slow if table have more than 200 million rows
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Subject: Re: [PERFORM] A Better External Sort?

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