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Re: Index scan is not working - Mailing list pgsql-general

From Kiran
Subject Re: Index scan is not working
Date
Msg-id CAJfd1U4P=pOS=XRK=2mKUuL2jhy+83y=jm=tBnPJr9viYyDMdQ@mail.gmail.com
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In response to Re: Index scan is not working  (Karsten Hilbert <Karsten.Hilbert@gmx.net>)
Responses Re: Index scan is not working  (Karsten Hilbert <Karsten.Hilbert@gmx.net>)
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Hi Karsten,

Thanks for the response.
I want to know whatever the Analyze output I am getting is normal for a table having few records or something is wrong.
Will the DB engine uses whatever the best way to execute a query irrespective of the indexing in this case?

At the moment the records in the table is very low but that column will be in thousands of rows in the near future. hence I wanted to confirm from the group am I doing something wrong here.

Also to_tsquery is casting to ::text. Is this normal ?

regards
Kiran



On Mon, Sep 19, 2016 at 2:33 PM, Karsten Hilbert <Karsten.Hilbert@gmx.net> wrote:
On Mon, Sep 19, 2016 at 02:10:50PM +0200, Kiran wrote:

> EXPLAIN ANALYZE select * from question where weighted_tsv @@
> to_tsquery('Hur&ofta');
>
> I get the following output
>
> "Bitmap Heap Scan on question  (cost=12.33..25.38 rows=10 width=731)
> (actual time=0.058..0.062 rows=3 loops=1)"
> "  Recheck Cond: (weighted_tsv @@ to_tsquery('Hur&ofta'::text))"
> "  Heap Blocks: exact=3"
> "  ->  Bitmap Index Scan on weighted_tsv_question_idx  (cost=0.00..12.33
> rows=10 width=0) (actual time=0.052..0.052 rows=3 loops=1)"
> "        Index Cond: (weighted_tsv @@ to_tsquery('Hur&ofta'::text))"
> "Planning time: 0.205 ms"
> "Execution time: 0.104 ms"
>
> Why the query is using the Bitmap ? Not the Index scan ?

You want PostgreSQL to use an index to try speed up a query
which takes 0.3 milliseconds to select 3 out of 10 rows ?

What is your exact workload that requires speedup of that
query ?

Karsten
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