Problem with inserts from subselects

I'm using postgres 7.3.x (the default installed on Fedora Core 1) and
I'm running into a serious
bug in the insert performance.

When I try a query like this...

<snip>

INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size)
(
select tmp.session, tmp.sent, tmp.data_row, tmp.direction_id, i.id,
tmp.price, tmp.size
FROM table_b tmp
INNER JOIN table_c i ON i.symbol_id = tmp.symbol_id AND i.route_id =
tmp.route_id
LIMIT 10
);

</snip>

the performance is really slow, that query takes about 10 seconds to
run. If I raise the limit to 100, it takes
10 times longer, etc.... It is basically so slow that we can't use our
database at all. However, if I just run the
inner select, like this....

<snip>
select tmp.session, tmp.sent, tmp.data_row, tmp.direction_id, i.id,
tmp.price, tmp.size
FROM table_b tmp
INNER JOIN table_c i ON i.symbol_id = tmp.symbol_id AND i.route_id =
tmp.route_id
LIMIT 10
</snip>

The result returns basically instantly, in less than half a second.

If I just insert the data by hand....

<snip>
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820183, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820184, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820185, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820186, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820187, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820188, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820189, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820190, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820191, 1, 852, 1.0, 10);
INSERT INTO table_a (session, sent, data_row, direction_id, instrument,
price, size) VALUES (1, NOW(), 820192, 1, 852, 1.0, 10);
</snip>

then it's fast again. The above query finishes all ten inserts in less
than half a second.

So it seems that the problem only occurs when inserting data from a
select clause, what's going on? And more importantly, how can I
fix it?

-Tyler
tjw19(at)columbia(dot)edu