Not sure what other options we have other than an EAV approach since we allow users to define their own attribute types (attribute type is in contacts_contactfield, attribute value is in values_value). Would you expect modelling that with a JSON column to perform better?
Thanks for the tips! On 23 February 2017 at 17:35, Pavel Stehule <pavel.steh...@gmail.com> wrote: > > > 2017-02-23 15:02 GMT+01:00 Rowan Seymour <rowanseym...@gmail.com>: > >> Hi Pavel. That suggestion gets me as far as LIMIT 694 with the fast plan >> then things get slow again. This is now what happens at LIMIT 695: >> >> Limit (cost=35945.78..50034.52 rows=695 width=88) (actual >> time=12852.580..12854.382 rows=695 loops=1) >> Buffers: shared hit=6 read=66689 >> -> Merge Join (cost=35945.78..56176.80 rows=998 width=88) (actual >> time=12852.577..12854.271 rows=695 loops=1) >> Merge Cond: (contacts_contact.id = contacts_contactgroup_contacts >> .contact_id) >> Buffers: shared hit=6 read=66689 >> -> Sort (cost=35944.53..35949.54 rows=2004 width=92) (actual >> time=12852.486..12852.577 rows=710 loops=1) >> Sort Key: contacts_contact.id >> Sort Method: quicksort Memory: 34327kB >> Buffers: shared hit=6 read=66677 >> -> Hash Join (cost=6816.19..35834.63 rows=2004 width=92) >> (actual time=721.293..12591.204 rows=200412 loops=1) >> Hash Cond: (contacts_contact.id = u0.contact_id) >> Buffers: shared hit=6 read=66677 >> -> Seq Scan on contacts_contact >> (cost=0.00..25266.00 rows=1000000 width=88) (actual time=0.003..267.258 >> rows=1000000 loops=1) >> Buffers: shared hit=1 read=15265 >> -> Hash (cost=6813.14..6813.14 rows=244 width=4) >> (actual time=714.373..714.373 rows=200412 loops=1) >> Buckets: 1024 Batches: 1 Memory Usage: 7046kB >> Buffers: shared hit=5 read=51412 >> -> HashAggregate (cost=6810.70..6813.14 >> rows=244 width=4) (actual time=561.099..644.822 rows=200412 loops=1) >> Buffers: shared hit=5 read=51412 >> -> Bitmap Heap Scan on values_value u0 >> (cost=60.98..6805.69 rows=2004 width=4) (actual time=75.410..364.976 >> rows=200412 loops=1) >> Recheck Cond: ((contact_field_id = >> 1) AND (upper(string_value) = 'F'::text)) >> Buffers: shared hit=5 read=51412 >> -> Bitmap Index Scan on >> values_value_field_string_value_contact (cost=0.00..60.47 rows=2004 >> width=0) (actual time=57.642..57.642 rows=200412 loops=1) >> Index Cond: >> ((contact_field_id = 1) AND (upper(string_value) = 'F'::text)) >> Buffers: shared hit=5 read=765 >> -> Index Only Scan Backward using >> contacts_contactgroup_contacts_contactgroup_id_0f909f73_uniq >> on contacts_contactgroup_contacts (cost=0.43..18967.29 rows=497992 >> width=4) (actual time=0.080..0.651 rows=1707 loops=1) >> Index Cond: (contactgroup_id = 1) >> Heap Fetches: 0 >> Buffers: shared read=12 >> Total runtime: 12863.938 ms >> >> https://explain.depesz.com/s/nfw1 >> >> Can you explain a bit more about what you mean about " dependency >> between contact_field_id = 1 and upper(string_value) = 'F'::text"? >> > > look to related node in plan > > > -> Hash (cost=6813.14..6813.14 rows=244 width=4) > (actual time=714.373..714.373 rows=200412 loops=1) > Buckets: 1024 Batches: 1 Memory Usage: 7046kB > Buffers: shared hit=5 read=51412 > -> HashAggregate (cost=6810.70..6813.14 > rows=244 width=4) (actual time=561.099..644.822 rows=200412 loops=1) > Buffers: shared hit=5 read=51412 > -> Bitmap Heap Scan on values_value u0 > (cost=60.98..6805.69 rows=2004 width=4) (actual time=75.410..364.976 > rows=200412 loops=1) > Recheck Cond: ((contact_field_id = > 1) AND (upper(string_value) = 'F'::text)) > Buffers: shared hit=5 read=51412 > > There is lot of significant differences between estimation (2004) and > reality (200412) - two orders - so the plan must be suboptimal > > I am looking to your schema - and it is variant on EAV table - this is > antippatern and for more then small returned rows it should be slow. > > Regards > > Pavel > > > >> Btw I created the index values_value_field_string_value_contact as >> >> CREATE INDEX values_value_field_string_value_contact >> ON values_value(contact_field_id, UPPER(string_value), contact_id DESC) >> WHERE contact_field_id IS NOT NULL; >> >> I'm not sure why it needs the contact_id column but without it the >> planner picks a slow approach for even smaller LIMIT values. >> >> >> On 23 February 2017 at 15:32, Pavel Stehule <pavel.steh...@gmail.com> >> wrote: >> >>> >>> >>> 2017-02-23 14:11 GMT+01:00 Rowan Seymour <rowanseym...@gmail.com>: >>> >>>> Hi guys >>>> >>>> I'm a bit stuck on a query that performs fantastically up to a certain >>>> limit value, after which the planner goes off in a completely different >>>> direction and performance gets dramatically worse. Am using Postgresql 9.3 >>>> >>>> You can see all the relevant schemas at http://pastebin.com/PNEqw2id >>>> and in the test database there are 1,000,000 records in contacts_contact, >>>> and about half of those will match the subquery on values_value. >>>> >>>> The query in question is: >>>> >>>> SELECT "contacts_contact".* FROM "contacts_contact" >>>> INNER JOIN "contacts_contactgroup_contacts" ON >>>> ("contacts_contact"."id" = "contacts_contactgroup_contact >>>> s"."contact_id") >>>> WHERE ("contacts_contactgroup_contacts"."contactgroup_id" = 1 >>>> AND "contacts_contact"."id" IN ( >>>> SELECT U0."contact_id" FROM "values_value" U0 WHERE >>>> (U0."contact_field_id" = 1 AND UPPER(U0."string_value"::text) = UPPER('F')) >>>> ) >>>> ) ORDER BY "contacts_contact"."id" DESC LIMIT 222; >>>> >>>> With that limit of 222, it performs like: >>>> >>>> Limit (cost=3.09..13256.36 rows=222 width=88) (actual >>>> time=0.122..3.358 rows=222 loops=1) >>>> Buffers: shared hit=708 read=63 >>>> -> Nested Loop (cost=3.09..59583.10 rows=998 width=88) (actual >>>> time=0.120..3.304 rows=222 loops=1) >>>> Buffers: shared hit=708 read=63 >>>> -> Merge Semi Join (cost=2.65..51687.89 rows=2004 width=92) >>>> (actual time=0.103..1.968 rows=227 loops=1) >>>> Merge Cond: (contacts_contact.id = u0.contact_id) >>>> Buffers: shared hit=24 read=63 >>>> -> Index Scan Backward using contacts_contact_pkey on >>>> contacts_contact (cost=0.42..41249.43 rows=1000000 width=88) (actual >>>> time=0.008..0.502 rows=1117 loops=1) >>>> Buffers: shared hit=22 read=2 >>>> -> Index Scan using values_value_field_string_value_contact >>>> on values_value u0 (cost=0.43..7934.72 rows=2004 width=4) (actual >>>> time=0.086..0.857 rows=227 loops=1) >>>> Index Cond: ((contact_field_id = 1) AND >>>> (upper(string_value) = 'F'::text)) >>>> Buffers: shared hit=2 read=61 >>>> -> Index Only Scan using >>>> contacts_contactgroup_contacts_contactgroup_id_0f909f73_uniq >>>> on contacts_contactgroup_contacts (cost=0.43..3.93 rows=1 width=4) (actual >>>> time=0.005..0.005 rows=1 loops=227) >>>> Index Cond: ((contactgroup_id = 1) AND (contact_id = >>>> contacts_contact.id)) >>>> Heap Fetches: 0 >>>> Buffers: shared hit=684 >>>> Total runtime: 3.488 ms >>>> >>>> https://explain.depesz.com/s/iPPJ >>>> >>>> But if increase the limit to 223 then it performs like: >>>> >>>> Limit (cost=8785.68..13306.24 rows=223 width=88) (actual >>>> time=2685.830..2686.534 rows=223 loops=1) >>>> Buffers: shared hit=767648 read=86530 >>>> -> Merge Join (cost=8785.68..29016.70 rows=998 width=88) (actual >>>> time=2685.828..2686.461 rows=223 loops=1) >>>> Merge Cond: (contacts_contact.id = >>>> contacts_contactgroup_contacts.contact_id) >>>> Buffers: shared hit=767648 read=86530 >>>> -> Sort (cost=8784.44..8789.45 rows=2004 width=92) (actual >>>> time=2685.742..2685.804 rows=228 loops=1) >>>> Sort Key: contacts_contact.id >>>> Sort Method: quicksort Memory: 34327kB >>>> Buffers: shared hit=767648 read=86524 >>>> -> Nested Loop (cost=6811.12..8674.53 rows=2004 >>>> width=92) (actual time=646.573..2417.291 rows=200412 loops=1) >>>> >>> >>> There is pretty bad estimation probably due dependency between >>> contact_field_id = 1 and upper(string_value) = 'F'::text >>> >>> The most simple solution is disable nested loop - set enable_nestloop to >>> off >>> >>> Regards >>> >>> Pavel >>> >>> >>>> Buffers: shared hit=767648 read=86524 >>>> -> HashAggregate (cost=6810.70..6813.14 rows=244 >>>> width=4) (actual time=646.532..766.200 rows=200412 loops=1) >>>> Buffers: shared read=51417 >>>> -> Bitmap Heap Scan on values_value u0 >>>> (cost=60.98..6805.69 rows=2004 width=4) (actual time=92.016..433.709 >>>> rows=200412 loops=1) >>>> Recheck Cond: ((contact_field_id = 1) >>>> AND (upper(string_value) = 'F'::text)) >>>> Buffers: shared read=51417 >>>> -> Bitmap Index Scan on >>>> values_value_field_string_value_contact (cost=0.00..60.47 rows=2004 >>>> width=0) (actual time=70.647..70.647 rows=200412 loops=1) >>>> Index Cond: ((contact_field_id = >>>> 1) AND (upper(string_value) = 'F'::text)) >>>> Buffers: shared read=770 >>>> -> Index Scan using contacts_contact_pkey on >>>> contacts_contact (cost=0.42..7.62 rows=1 width=88) (actual >>>> time=0.007..0.007 rows=1 loops=200412) >>>> Index Cond: (id = u0.contact_id) >>>> Buffers: shared hit=767648 read=35107 >>>> -> Index Only Scan Backward using >>>> contacts_contactgroup_contacts_contactgroup_id_0f909f73_uniq on >>>> contacts_contactgroup_contacts (cost=0.43..18967.29 rows=497992 width=4) >>>> (actual time=0.073..0.273 rows=550 loops=1) >>>> Index Cond: (contactgroup_id = 1) >>>> Heap Fetches: 0 >>>> Buffers: shared read=6 >>>> Total runtime: 2695.301 ms >>>> >>>> https://explain.depesz.com/s/gXS >>>> >>>> I've tried running ANALYZE but that actually reduced the limit at which >>>> things get worse. Any insight into the reasoning of the query planner would >>>> be much appreciated. >>>> >>>> Thanks >>>> >>>> -- >>>> *Rowan Seymour* | +260 964153686 <+260%2096%204153686> | @rowanseymour >>>> >>> >>> >> >> >> -- >> *Rowan Seymour* | +260 964153686 <+260%2096%204153686> | @rowanseymour >> > > -- *Rowan Seymour* | +260 964153686 | @rowanseymour
