On Sat, Jan 24, 2015 at 9:41 PM, Joe Van Dyk <j...@tanga.com> wrote:
> I have an events table that records page views and purchases (type = > 'viewed' or type='purchased'). I have a query that figures out "people who > bought/viewed this also bought/viewed that". > > It worked fine, taking about 0.1 seconds to complete, until a few hours > ago when it started taking hours to complete. Vacuum/analyze didn't help. > Turned out there was one session_id that had 400k rows in the system. > Deleting that made the query performant again. > > Is there anything I can do to make the query work better in cases like > that? Missing index, or better query? > > This is on 9.3.5. > > The below is reproduced at the following URL if it's not formatted > correctly in the email. > https://gist.githubusercontent.com/joevandyk/cb8f4afdb6c1b178c606/raw/9940bbe033ebd56d38caa46e33c1ddfd9df36eda/gistfile1.txt > > explain select > e1.product_id, > e2.site_id, > e2.product_id, > count(nullif(e2.type='viewed', false)) view_count, > count(nullif(e2.type='purchased', false)) purchase_count > from events e1 > join events e2 on e1.session_id = e2.session_id and e1.type = e2.type > where > e1.product_id = '82503' and > e1.product_id != e2.product_id > group by e1.product_id, e2.product_id, e2.site_id; > QUERY PLAN > ---------------------------------------------------------------------------------------------------------------------------- > GroupAggregate (cost=828395.67..945838.90 rows=22110 width=19) > -> Sort (cost=828395.67..840117.89 rows=4688885 width=19) > Sort Key: e1.product_id, e2.product_id, e2.site_id > -> Nested Loop (cost=11.85..20371.14 rows=4688885 width=19) > -> Bitmap Heap Scan on events e1 (cost=11.29..1404.31 > rows=369 width=49) > Recheck Cond: (product_id = '82503'::citext) > -> Bitmap Index Scan on events_product_id_site_id_idx > (cost=0.00..11.20 rows=369 width=0) > Index Cond: (product_id = '82503'::citext) > -> Index Scan using events_session_id_type_product_id_idx on > events e2 (cost=0.56..51.28 rows=12 width=51) > Index Cond: ((session_id = e1.session_id) AND (type = > e1.type)) > Filter: (e1.product_id <> product_id) > (11 rows) > > recommender_production=> \d events > Table "public.events" > Column | Type | Modifiers > -------------+--------------------------+----------------------------------------------------- > id | bigint | not null default > nextval('events_id_seq'::regclass) > user_id | citext | > session_id | citext | not null > product_id | citext | not null > site_id | citext | not null > type | text | not null > happened_at | timestamp with time zone | not null > created_at | timestamp with time zone | not null > Indexes: > "events_pkey" PRIMARY KEY, btree (id) > "events_product_id_site_id_idx" btree (product_id, site_id) > "events_session_id_type_product_id_idx" btree (session_id, type, > product_id) > Check constraints: > "events_session_id_check" CHECK (length(session_id::text) < 255) > "events_type_check" CHECK (type = ANY (ARRAY['purchased'::text, > 'viewed'::text])) > "events_user_id_check" CHECK (length(user_id::text) < 255) > > > > After removing the session with 400k events, I was able to do an explain analyze, here is one of them: http://explain.depesz.com/s/PFNk
