ERROR: could not open segment 1 of relation 1663/743352/743420 (target block 6407642): No such file or directory

Hi guys,

We upgraded from 8.3.5 to 8.3.9 yesterday, after an extended period of
testing, to 8.3.10 today in hope of fixing it, and we're getting the following
error on occasion.

ERROR: could not open segment 1 of relation 1663/743352/743420 (target block
2171336): No such file or directory
CONTEXT: SQL statement "SELECT day FROM min_stats WHERE day<= $1 AND
unique_ip=-1 ORDER BY day DESC LIMIT 1"
PL/pgSQL function "update_unique_ips" line 13 at SQL statement

update_unique_ips() is called once per minute, but we get anywhere from one
error per minute, to one error per hour.

Relation 743420 in database 743352 is 441270272 bytes long and growing by a
few thousand bytes here and there.
Obviously, as we've gone from 8.3.9 to 8.3.10, we're restarted postgres a few
times. We have also REINDEXd each table, the database, dropped and re-created
all the indexes.
I've even pg_dump'd the database, and loaded it into a fresh database. The
relation numbers changed, but the 1663 bit remained the same.

Best I can tell it's this bit of code from the beginning of
update_unique_ips() that's doing it, but it seems completely innocuous to me.

CREATE FUNCTION update_unique_ips() RETURNS timestamp without time zone
AS $$

DECLARE
last_day timestamp;
day_for_update timestamp;

BEGIN
-- declare last_day
SELECT INTO last_day day-interval '30 min' as day
FROM min_stats
ORDER BY day DESC
LIMIT 1;

SELECT INTO day_for_update day
FROM min_stats
WHERE day<=last_day AND unique_ip=-1
ORDER BY day DESC
LIMIT 1;

Could anyone help us out here please?
Thanks

--
Mike Williams