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ERROR: cache lookup failed for function 0

From: "David E(dot) Wheeler" <david(at)kineticode(dot)com>
To: pgsql-bugs(at)postgresql(dot)org
Subject: ERROR: cache lookup failed for function 0
Date: 2008-10-22 19:33:59
Message-ID: C43141E7-2EC6-491B-8CE2-A569AE53576B@kineticode.com (view raw or flat)
Thread:
Lists: pgsql-bugs
Howdy,

I ran into this error on 8.2 a while ago, and just figured out what  
was causing it. Here's a quick example on 8.2:

BEGIN;

-- Compare name[]s more or less like 8.3 does.
CREATE OR REPLACE FUNCTION namearray_text(name[])
RETURNS TEXT AS 'SELECT textin(array_out($1));'
LANGUAGE sql IMMUTABLE STRICT;

CREATE CAST (name[] AS text) WITH FUNCTION namearray_text(name[]) AS  
IMPLICIT;

CREATE OR REPLACE FUNCTION namearray_eq( name[], name[] )
RETURNS bool
AS 'SELECT $1::text = $2::text;'
LANGUAGE sql IMMUTABLE STRICT;

CREATE OPERATOR = (
     LEFTARG    = name[],
     RIGHTARG   = name[],
     NEGATOR    = <>,
     PROCEDURE  = namearray_eq
);

SELECT '{foo}'::name[] <> '{bar}'::name[];

ROLLBACK;

If you comment out the NEGATOR line, the error is changed to the more  
useful

   ERROR:  operator is not unique: name[] <> name[]

I'm assuming that, if you did this for 8.3 (which has name[]  
comparison operators in core, so it'd have to be an operator with some  
other type), you'd get the same useless error.

Ideally, in the situation where a NEGATOR (or commutator, too?) is  
specified but has not actually been defined, you'd get an error such as:

   ERROR:  operator not defined: name[] <> name[]

Thanks,

David

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