Message-ID: <1520330344.2601.15.camel@cybertec.at>
Subject: Re: GIST index (polygon, point)
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: ghiureai <isabella.ghiurea@nrc-cnrc.gc.ca>,
	"pgsql-performance@postgresql.org"
	 <pgsql-performance@postgresql.org>
Date: Tue, 06 Mar 2018 10:59:04 +0100
In-Reply-To: <f3102e7a-a1bd-026c-fbbc-9a50d9c7b68b@nrc-cnrc.gc.ca>
References: <f3102e7a-a1bd-026c-fbbc-9a50d9c7b68b@nrc-cnrc.gc.ca>
Organization: Cybertec
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ghiureai wrote:
> I have a short description bellow from Dev team regarding the behaviour of gist index on the polygon column, looking to get some  feedback  from you:
>
> ".... I was expecting the <@(point,polygon) and @>(polygon,point) to be indexable but they are not. see bellow query output ,
> the column is a polygon and the index is a gist index on the polygon column; my understanding of the above query is that it says which operators would cause that index to be used
>
> This SQL shows which operators are indexable:SELECT
>  pg_get_indexdef(ss.indexrelid, (ss.iopc).n, TRUE) AS index_col,
>  amop.amopopr::regoperator AS indexable_operator
> FROM pg_opclass opc, pg_amop amop,
>  (SELECT indexrelid, information_schema._pg_expandarray(indclass) AS iopc
>   FROM pg_index
>   WHERE indexrelid = 'caom2.Plane_energy_ib'::regclass) ss
> WHERE amop.amopfamily = opc.opcfamily AND opc.oid = (ss.iopc).x
> ORDER BY (ss.iopc).n, indexable_operator;
>
> We run  the SQL  in PG 9.5.3 and PG 10.2 we  the same result: only polygon vs polygon is indexable (except the last entry which is distance operator).
> The work around for us was to change interval-contains-value from polygon-contains-point (@> or <@ operator) to
> polygn-intersects-really-small-polygon (&&) in order to use the index, but I was quite surprised that contains operators are not indexable!
> Note that this is using the built in polygon and not pgsphere (spoly)"

That sounds about right.

You could use a single-point polygon like '((1,1))'::polygon
and the <@ or && operator.

Yours,
Laurenz Albe
-- 
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