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Thread: [BUGS] "could not open relation with OID XXX" when using recreated index insql function

[BUGS] "could not open relation with OID XXX" when using recreated index insql function

From
Krystian Szladewski
Date:
Hi guys,

I think I found a bug in sql (not plpgsql) functions. 
This is the error I’m getting:

ERROR:  XX000: could not open relation with OID 13053550
CONTEXT:  SQL function "fail" statement 3
LOCATION:  relation_open, heapam.c:1130

It happens when I try to recreate an index and use it afterwards (both within the function).

My postgres version:
PostgreSQL 9.6.2 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.2 20140120 (Red Hat 4.8.2-16), 64-bit

Here is some sql to reproduce it:

BEGIN;

CREATE TABLE test_1 (
    test_id     BIGINT PRIMARY KEY,
    other_id    BIGINT NOT NULL
);
CREATE INDEX test_1_other_idx ON test_1(other_id);

— Make sure query planner uses the index scan
SET enable_seqscan=off;

CREATE OR REPLACE FUNCTION fail() RETURNS bigint
LANGUAGE sql AS
$$
    -- Re-create the index
    DROP INDEX IF EXISTS test_1_other_idx;
    CREATE INDEX test_1_other_idx ON test_1(other_id);

    -- Fail!
    SELECT test_id FROM test_1 WHERE other_id = 1000;
$$;

SELECT fail();

ROLLBACK;


If you modify this function to use plpgsql, it won’t fail anymore:

CREATE OR REPLACE FUNCTION ok() RETURNS bigint
LANGUAGE plpgsql AS
$$
    BEGIN

    -- Re-create the index
    DROP INDEX IF EXISTS test_1_other_idx;
    CREATE INDEX test_1_other_idx ON test_1(other_id);

    RETURN (SELECT test_id FROM test_1 WHERE other_id = 1);

    END
$$;

SELECT ok();


It also works fine when you paste contents of fail() function into psql session.


Best Regards,
Krystian Szladewski


Re: [BUGS] "could not open relation with OID XXX" when using recreated index in sql function

From
Tom Lane
Date:
Krystian Szladewski <krystian.szladewski@adspert.de> writes:
> CREATE OR REPLACE FUNCTION fail() RETURNS bigint
> LANGUAGE sql AS
> $$
>     -- Re-create the index
>     DROP INDEX IF EXISTS test_1_other_idx;
>     CREATE INDEX test_1_other_idx ON test_1(other_id);

>     -- Fail!
>     SELECT test_id FROM test_1 WHERE other_id = 1000;
> $$;

Yeah, this is unsurprising per the NOTE here:
https://www.postgresql.org/docs/current/static/xfunc-sql.html
       Note: The entire body of a SQL function is parsed before any of it       is executed. While a SQL function can
containcommands that alter       the system catalogs (e.g., CREATE TABLE), the effects of such       commands will not
bevisible during parse analysis of later       commands in the function. Thus, for example, CREATE TABLE foo
(...);INSERT INTO foo VALUES(...); will not work as desired if       packaged up into a single SQL function, since foo
won'texist yet       when the INSERT command is parsed. It's recommended to use       PL/PgSQL instead of a SQL
functionin this type of situation.
 

(I see that this NOTE only talks about parse analysis, but actually
the planning is done in one fell swoop as well, which is what leads to
your problem.)

At some point somebody will probably rewrite the SQL function executor
to fix this, and get rid of some of its other unpleasant properties
like not using the plancache; but it hasn't been high priority.
        regards, tom lane


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