Re: Indexes not used in DELETE

From: Tom Lane
Subject: Re: Indexes not used in DELETE
Date: ,
Msg-id: 6572.1241737616@sss.pgh.pa.us
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In response to: Indexes not used in DELETE  (Viktor Rosenfeld <-berlin.de>)
Responses: Re: Indexes not used in DELETE  (Viktor Rosenfeld <-berlin.de>)
List: pgsql-performance

Viktor Rosenfeld <-berlin.de> writes:
>                             ->  Seq Scan on corpus toplevel (cost=0.00..1.39 rows=1 width=54)
>                                   Filter: (top_level AND (id = 25::numeric))

> Specifically, I'm wondering why the innermost scan on corpus
> (toplevel) does not use the index idx_corpus__toplevel

The cost estimate indicates that there are so few rows in corpus
that an indexscan would be a waste of time.

> and why the
> join between corpus (toplevel) and corpus (child) is not a merge join
> using the index corpus_pre_key to access the child table.

Same answer.  Populate the table and the plan will change.

            regards, tom lane


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