From: ktm@rice.edu <ktm@rice.edu>
To: Michael Barker <mikeb01@gmail.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: Query doesn't use index on hstore column
Date: Thu, 4 Dec 2014 15:46:25 -0600
Message-ID: <20141204214625.GG20516@aart.rice.edu> (raw)
In-Reply-To: <CALwNKeTZyva2ev5dFDXs4PX01yk27Rk5-UCSYhCWh+jnyDTNNA@mail.gmail.com>
References: <CALwNKeTZyva2ev5dFDXs4PX01yk27Rk5-UCSYhCWh+jnyDTNNA@mail.gmail.com>
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On Fri, Dec 05, 2014 at 09:42:20AM +1300, Michael Barker wrote:
> 1) Created table with hstore column and btree index.
>
> barkerm=# \d audit
> Table "public.audit"
> Column | Type |
> Modifiers
> ---------------+-----------------------------+----------------------------------------------------
> id | integer | not null default
> nextval('audit_id_seq'::regclass)
> principal_id | integer |
> created_at | timestamp without time zone |
> root | character varying(255) |
> template_code | character(3) |
> attributes | hstore |
> args | character varying(255)[] |
> Indexes:
> "audit_pkey" PRIMARY KEY, btree (id)
> "audit_attributes_idx" btree (attributes)
>
> ...
> 5) Explain query using the attributes column in the where clause (uses Seq
> Scan).
>
> barkerm=# explain analyse select * from audit where attributes->'accountId'
> = '1879355460';
> QUERY PLAN
>
> ------------------------------------------------------------------------------------------------------------
> Seq Scan on audit (cost=0.00..35409.00 rows=5000 width=133) (actual
> time=114.314..218.821 rows=1 loops=1)
> Filter: ((attributes -> 'accountId'::text) = '1879355460'::text)
> Rows Removed by Filter: 999999
> Planning time: 0.074 ms
> Execution time: 218.843 ms
> (5 rows)
>
Hi Michael,
I think your index definitions need to be on the particular attribute from
attributes and not attributes itself. That works but it does not apply to
the query you show above. I think that the binary json type in 9.4 will
do what you want. I have not worked with it myself, just looked at the docs.
Regards,
Ken
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To: pgsql-performance@postgresql.org
Cc: ktm@rice.edu, mikeb01@gmail.com
Subject: Re: Query doesn't use index on hstore column
In-Reply-To: <20141204214625.GG20516@aart.rice.edu>
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