From: Tom Lane <tgl@sss.pgh.pa.us>
To: AlexK <alkuzo@gmail.com>
cc: pgsql-sql@postgresql.org
Subject: Re: Is there an upper limit on the size of an array if it is indexed?
In-reply-to: <1393273817988-5793380.post@n5.nabble.com>
References: <1393273817988-5793380.post@n5.nabble.com>
Comments: In-reply-to AlexK <alkuzo@gmail.com>
 message dated "Mon, 24 Feb 2014 12:30:18 -0800"
Date: Mon, 24 Feb 2014 15:39:55 -0500
Message-ID: <9198.1393274395@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-sql-owner@postgresql.org

AlexK <alkuzo@gmail.com> writes:
> I have created a unique index on an array of integers, and it works for a
> small test case:

> create table i(id int not null primary key,
> v int[] not null unique );

> insert into i(id, v) values(1, ARRAY[1,2]);

> -- fails
> insert into i(id, v) values(2, ARRAY[1,2]);
> -- succeeds
> insert into i(id, v) values(2, ARRAY[2,1]);

> Is there an upper limit on the size of an array being indexed? I am
> currently considering arrays of 2K-3K integers.

PG btrees have an item size limit of a couple of KB, so I don't think
this is going to work well for you.

Some people have gotten around that by using a unique index on a hash
value.  If you use something like MD5, the odds of a false collision
are probably low enough to tolerate.

			regards, tom lane


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