Re: Simple Join

On Thursday 15 December 2005 00:52, you wrote:
> On Wed, 2005-12-14 at 17:47 -0500, Tom Lane wrote:
> > That plan looks perfectly fine to me. You could try forcing some other
> > choices by fooling with the planner enable switches (eg set
> > enable_seqscan = off) but I doubt you'll find much improvement. There
> > are too many rows being pulled from ordered_products to make an index
> > nestloop a good idea.
>
> Well, I'm no expert either, but if there was an index on
> ordered_products (paid, suspended_sub, id) it should be mergejoinable
> with the index on to_ship.ordered_product_id, right? Given the
> conditions on paid and suspended_sub.
>
> If you (Kevin) try adding such an index, ideally it would get used given
> that you're only pulling out a small fraction of the rows in to_ship.
> If it doesn't get used, then I had a similar issue with 8.0.3 where an
> index that was mergejoinable (only because of the restrictions in the
> where clause) wasn't getting picked up.

The following is already there:

CREATE INDEX ordered_product_id_index
ON to_ship
USING btree
(ordered_product_id);

That's why I emailed this list.

> Mitch
>
> Kevin Brown wrote:
> > CREATE TABLE to_ship
> > (
> > id int8 NOT NULL DEFAULT nextval(('to_ship_seq'::text)::regclass),
> > ordered_product_id int8 NOT NULL,
> > bounced int4 NOT NULL DEFAULT 0,
> > operator_id varchar(20) NOT NULL,
> > "timestamp" timestamptz NOT NULL DEFAULT ('now'::text)::timestamp(6)
> > with
> > time zone,
> > CONSTRAINT to_ship_pkey PRIMARY KEY (id),
> > CONSTRAINT to_ship_ordered_product_id_fkey FOREIGN KEY
> > (ordered_product_id)
> > REFERENCES ordered_products (id) ON UPDATE RESTRICT ON DELETE RESTRICT
> > )
> > WITHOUT OIDS;
> >
> > CREATE TABLE ordered_products
> > (
> > id int8 NOT NULL DEFAULT
> > nextval(('ordered_products_seq'::text)::regclass),
> > order_id int8 NOT NULL,
> > product_id int8 NOT NULL,
> > recipient_address_id int8 NOT NULL,
> > hide bool NOT NULL DEFAULT false,
> > renewal bool NOT NULL DEFAULT false,
> > "timestamp" timestamptz NOT NULL DEFAULT ('now'::text)::timestamp(6)
> > with
> > time zone,
> > operator_id varchar(20) NOT NULL,
> > suspended_sub bool NOT NULL DEFAULT false,
> > quantity int4 NOT NULL DEFAULT 1,
> > price_paid numeric NOT NULL,
> > tax_paid numeric NOT NULL DEFAULT 0,
> > shipping_paid numeric NOT NULL DEFAULT 0,
> > remaining_issue_obligation int4 NOT NULL DEFAULT 0,
> > parent_product_id int8,
> > delivery_method_id int8 NOT NULL,
> > paid bool NOT NULL DEFAULT false,
> > CONSTRAINT ordered_products_pkey PRIMARY KEY (id),
> > CONSTRAINT ordered_products_order_id_fkey FOREIGN KEY (order_id)
> > REFERENCES
> > orders (id) ON UPDATE RESTRICT ON DELETE RESTRICT,
> > CONSTRAINT ordered_products_parent_product_id_fkey FOREIGN KEY
> > (parent_product_id) REFERENCES ordered_products (id) ON UPDATE
> > RESTRICT ON
> > DELETE RESTRICT,
> > CONSTRAINT ordered_products_recipient_address_id_fkey FOREIGN KEY
> > (recipient_address_id) REFERENCES addresses (id) ON UPDATE RESTRICT ON
> > DELETE
> > RESTRICT
> > )
> > WITHOUT OIDS;
> >
> > === The two indexes that should matter ===
> > CREATE INDEX ordered_product_id_index
> > ON to_ship
> > USING btree
> > (ordered_product_id);
> >
> > CREATE INDEX paid_index
> > ON ordered_products
> > USING btree
> > (paid);
> >
> > ordered_products.id is a primary key, so it should have an implicit
> > index.