Hi,
When I run the SQL below, I get an error on the third call to foo() : "ERROR:
could not open relation with OID 884693". I'm quite sure this OID belongs to
the TOAST table corresponding to the temporary table created by foo() during
the third call. The fourth call works fine again.
I suspect the third one fails because the data is too large (even when
compressed) to be stored without using toast. I can't reproduce the issue if
for example I use a long string of identical characters instead of "random"
ones. My guess would be that the TOAST table is still somehow referenced by the
result value, even though the table itself has been dropped by the time the
result value is used.
I have tested this myself on 8.4.4 and it has also been verified on a 9.1 by
someone on #postgresql.
Kind regards,
Matthijs Bomhoff
CREATE OR REPLACE FUNCTION foo(size_ INTEGER) RETURNS TEXT AS $EOF$
DECLARE
acc_ TEXT := '';
cur_rec_ RECORD;
BEGIN
EXECUTE 'CREATE TEMPORARY TABLE foo_tab(blob TEXT NOT NULL)';
-- Construct a string with random characters to prevent compression (with
high probability)
LOOP
EXIT WHEN length(acc_) >= size_;
acc_ := acc_ || chr(ceil(random()*64)::integer + 32);
END LOOP;
EXECUTE 'INSERT INTO foo_tab(blob) values (' || quote_literal(acc_) || ')';
EXECUTE 'SELECT * FROM foo_tab LIMIT 1' INTO cur_rec_;
EXECUTE 'DROP TABLE foo_tab';
RETURN cur_rec_.blob;
END
$EOF$ LANGUAGE plpgsql;
SELECT md5(foo(10));
SELECT md5(foo(20));
SELECT md5(foo(40000)); -- This one breaks on my 8.4.4
SELECT md5(foo(30)); -- And this one works fine again
DROP FUNCTION foo(INTEGER);
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