Re: Query performance

On Sat, Jan 24, 2015 at 10:12 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
wrote:

> Hi
>
> this plan looks well
>
> Regards
>
> Pavel
>

Here's one that's not quite as well: http://explain.depesz.com/s/SgT

Joe

>
> 2015-01-25 6:45 GMT+01:00 Joe Van Dyk <joe(at)tanga(dot)com>:
>
>> Oops, didn't run vacuum analyze after deleting the events. Here is
>> another 'explain analyze': http://explain.depesz.com/s/AviN
>>
>> On Sat, Jan 24, 2015 at 9:43 PM, Joe Van Dyk <joe(at)tanga(dot)com> wrote:
>>
>>> On Sat, Jan 24, 2015 at 9:41 PM, Joe Van Dyk <joe(at)tanga(dot)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
>>>
>>
>>
>