Kevin Brown wrote:
I only had two explicit indexes. One was on to_ship.ordered_product_id and
the other was on ordered_products.paid. ordered_products.id is a primary
key. This is on your query with an index added on suspended_sub:
dli=# explain analyze SELECT ordered_products.product_id
dli-# FROM to_ship INNER JOIN ordered_products
dli-# ON (to_ship.ordered_product_id = ordered_products.id
dli(# AND ordered_products.paid = TRUE AND
dli(# ordered_products.suspended_sub = FALSE);
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------
Hash Join (cost=5126.19..31528.40 rows=20591 width=8) (actual
time=4554.190..23519.618 rows=14367 loops=1)
Hash Cond: ("outer".ordered_product_id = "inner".id)
-> Seq Scan on to_ship (cost=0.00..11529.12 rows=611612 width=8) (actual
time=11.254..15192.042 rows=611612 loops=1)
-> Hash (cost=4954.79..4954.79 rows=21759 width=16) (actual
time=4494.900..4494.900 rows=18042 loops=1)
-> Index Scan using paid_index on ordered_products
(cost=0.00..4954.79 rows=21759 width=16) (actual time=72.431..4414.697
rows=18042 loops=1)
Index Cond: (paid = true)
Filter: (paid AND (NOT suspended_sub))
Total runtime: 23532.785 ms
(8 rows)
Well - that had no effect at all :-) You don't have and index on
to_ship.ordered_product_id do you? - try adding one (ANALYZE again), and
let use know what happens (you may want to play with SET
enable_seqscan=off as well).
And also, if you are only ever interested in paid = true and
suspended_sub = false, then you can recreate these indexes as partials -
e.g:
CREATE INDEX paid_index ON ordered_products (paid) WHERE paid = true;
CREATE INDEX suspended_sub_index ON ordered_products (suspended_sub)
WHERE suspended_sub = false;
So what's the best way to performance wiggle this info out of the db? The
list of values is only about 30 tuples long out of this query, so I was
figuring I could trigger on insert to to_ship to place the value into another
table if it didn't already exist. I'd rather the writing be slow than the
reading.
Yeah - all sort of horrible denormalizations are possible :-), hopefully
we can get the original query to work ok, and avoid the need to add code
or triggers to you app.
