Re: Simple Join

On 12/14/05, Kevin Brown <blargity(at)gmail(dot)com> wrote:
> I'll just start by warning that I'm new-ish to postgresql.
>
> I'm running 8.1 installed from source on a Debian Sarge server. I have a
> simple query that I believe I've placed the indexes correctly for, and I
> still end up with a seq scan. It makes sense, kinda, but it should be able
> to use the index to gather the right values. I do have a production set of
> data inserted into the tables, so this is running realistically:
>

what hardware?

> dli=# explain analyze SELECT ordered_products.product_id
> dli-# FROM to_ship, ordered_products
> dli-# WHERE to_ship.ordered_product_id = ordered_products.id AND
> dli-# 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=6517.438..25123.115 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=393.206..15711.715 rows=611612 loops=1)
> -> Hash (cost=4954.79..4954.79 rows=21759 width=16) (actual
> time=6076.153..6076.153 rows=18042 loops=1)
> -> Index Scan using paid_index on ordered_products
> (cost=0.00..4954.79 rows=21759 width=16) (actual time=136.472..5966.275
> rows=18042 loops=1)
> Index Cond: (paid = true)
> Filter: (paid AND (NOT suspended_sub))
> Total runtime: 25136.190 ms
> (8 rows)
>

show the tables and the indexes for those tables

> This is running on just about the world's slowest server (with a laptop hard
> drive to boot), but how can I avoid the seq scan, or in general speed up this
> query?
>
> to_ship will have far less tuples than ordered_products, but it's still not
> small, as you can see.
>

--
regards,
Jaime Casanova
(DBA: DataBase Aniquilator ;)