Problem with index not being chosen inside PL/PgSQL function...

Hi all,

Thanks to those on this list who contribute their knowledge for our consumption! I have another question:

The problem I'm having is in one particular spot where I'm trying to run a "parametized" query inside a PL/PgSQL function. When I run the query directly, the planner correctly chooses to use an index. When I run the query with hard-coded values inside the function, the planner uses the index again. However, when I try to pass in one of the values as a parameter, the query suddenly takes 45+ seconds to run (and is obviously no longer using the query). Inside the function, I've tried using bound cursors, unbound cursors, and a direct query as shown in the test_unlock function below.

Here are the details:

EXPLAIN ANALYZE SELECT ah.* FROM alert ah WHERE ( (ah.replaced_by_id = '0') AND (ah.not_displayed_id = '7714598') );

"Index Scan using idx_acurr on alert ah (cost=0.00..4.44 rows=1 width=768) (actual time=61.100..61.100 rows=0 loops=1)"
" Index Cond: ((replaced_by_id = 0) AND (not_displayed_id = 7714598))"
"Total runtime: 61.459 ms"

CREATE OR REPLACE FUNCTION test_unlock ( id_locked alert.id%TYPE ) RETURNS alert.id%TYPE AS $test_unlock$
DECLARE
last_alert alert%ROWTYPE;
BEGIN
RAISE NOTICE 'Fetching data...';
SELECT ah.* INTO last_alert FROM alert ah where ( (ah.replaced_by_id = '0') AND (ah.not_displayed_id = id_locked ) );
RAISE NOTICE 'Data fetched...';

IF NOT FOUND THEN
RAISE NOTICE 'No locked out alert was found!';
ELSE
RAISE NOTICE 'Alert id % was found!', last_alert.id;
END IF;

RETURN last_alert.id;
END;
$test_unlock$ LANGUAGE plpgsql;

SELECT * FROM test_unlock( '7714598');

Using the function, I get a 45+ second delay between the "fetching" notice and the "fetched" notice. Is there some way I can help the planner out further? I ever tried adding an 'ORDER BY replaced_by_id, not_displayed_id" to help it "find" the index, but no luck there...

Thanks in advance for any help!

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