Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) - Mailing list pgsql-performance
From | Adrian Klaver |
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Subject | Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) |
Date | |
Msg-id | 92fe033c-0221-30e3-1143-de8b0c8d923b@aklaver.com Whole thread Raw |
In response to | Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) (Amarendra Konda <amar.vijaya@gmail.com>) |
Responses |
Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery )
("David G. Johnston" <david.g.johnston@gmail.com>)
Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) ("David G. Johnston" <david.g.johnston@gmail.com>) Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) (Amarendra Konda <amar.vijaya@gmail.com>) Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) (Amarendra Konda <amar.vijaya@gmail.com>) |
List | pgsql-performance |
On 5/7/20 4:19 AM, Amarendra Konda wrote: > Hi, > > PostgreSQL version : PostgreSQL 9.6.2 on x86_64-pc-linux-gnu, compiled > by gcc (GCC) 4.8.3 20140911 (Red Hat 4.8.3-9), 64-bit > > We have noticed huge difference interms of execution plan ( response > time) , When we pass the direct values Vs inner query to IN clause. > > High level details of the use case are as follows > > * As part of the SQL there are 2 tables named Process_instance > (master) and Process_activity ( child) > * Wanted to fetch TOP 50 rows from Process_activity table for the > given values of the Process_instance. > * When we used Inner Join / Inner query ( query1) between parent > table and child table , LIMIT is not really taking in to account. > Instead it is fetching more rows and columns that required, and > finally limiting the result It is doing what you told it to do which is SELECT all process_instance_i's for user_id='317079413683604' and app_id = '427380312000560' and then filtering further. I am going to guess that if you run the inner query alone you will find it returns ~23496 rows. You might have better results if you an actual join between process_activity and process_instance. Something like below(obviously not tested): SELECT pa.process_activity_id FROM process_activity pa JOIN process_instance pi ON pa.process_instance_id = pi.process_instance_id WHERE pa.app_id = '427380312000560' AND pa.created > '1970-01-01 00:00:00' AND pi.user_id = '317079413683604' ORDER BY pa.process_instance_id, pa.created LIMIT 50; The second query is not equivalent as you are not filtering on user_id and you are filtering on only three process_instance_id's. > * > > > *Query1* > > web_1=> EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS) SELECT > pa.process_activity_id FROM process_activity pa WHERE pa.app_id = > '427380312000560' AND pa.created > '1970-01-01 00:00:00' AND > pa.process_instance_id in *_(SELECT pi.process_instance_id FROM > process_instance pi WHERE pi.user_id = '317079413683604' AND pi.app_id = > '427380312000560')_* ORDER BY pa.process_instance_id,pa.created limit 50; > > > QUERY PLAN > > ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ > Limit (cost=1071.47..1071.55 rows=31 width=24) (actual > time=85.958..85.991 rows=50 loops=1) > Output: pa.process_activity_id, pa.process_instance_id, pa.created > Buffers: shared hit=43065 > -> Sort (cost=1071.47..1071.55 rows=31 width=24) (actual > time=85.956..85.971 rows=50 loops=1) > Output: pa.process_activity_id, pa.process_instance_id, pa.created > Sort Key: pa.process_instance_id, pa.created > Sort Method: top-N heapsort Memory: 28kB > Buffers: shared hit=43065 > -> Nested Loop (cost=1.14..1070.70 rows=31 width=24) (actual > time=0.031..72.183 rows=46992 loops=1) > Output: pa.process_activity_id, pa.process_instance_id, > pa.created > Buffers: shared hit=43065 > -> Index Scan using fki_conv_konotor_user_user_id on > public.process_instance pi (cost=0.43..2.66 rows=1 width=8) (actual > time=0.010..0.013 rows=2 loops=1) > Output: pi.process_instance_id > Index Cond: (pi.user_id = '317079413683604'::bigint) > Filter: (pi.app_id = '427380312000560'::bigint) > Buffers: shared hit=5 > -> Index Scan using > process_activity_process_instance_id_app_id_created_idx on > public.process_activity pa (cost=0.70..1053.80 rows=1425 width=24) > (actual time=0.015..20.702 rows=*23496* loops=2) > * Output: pa.process_activity_id, pa.process_activity_type, > pa.voice_url, pa.process_activity_user_id, pa.app_id, > pa.process_instance_id, pa.alias, pa.read_by_user, pa.source, > pa.label_category_id, pa.label_id, pa.csat_response_id, > pa.process_activity_fragments, pa.created, pa.updated, pa.rule_id, pa.market > ing_reply_id, pa.delivered_at, pa.reply_fragments, pa.status_fragment, > pa.internal_meta, pa.interaction_id, pa.do_not_translate, > pa.should_translate, pa.in_reply_to* > Index Cond: ((pa.process_instance_id = > pi.process_instance_id) AND (pa.app_id = '427380312000560'::bigint) AND > (pa.created > '1970-01-01 00:00:00'::timestamp without time zone)) > Buffers: shared hit=43060 > Planning time: 0.499 ms > Execution time: 86.040 ms > (22 rows) > > *_Query 2_* > > web_1=> EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS) SELECT > pa.process_activity_id AS m_process_activity_id FROM process_activity m > WHERE pa.app_id = '427380312000560' AND pa.created > '1970-01-01 > 00:00:00' AND pa.process_instance_id in > (*240117466018927,325820556706970,433008275197305*) ORDER BY > pa.process_instance_id,pa.created limit 50; > > QUERY PLAN > --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > Limit (cost=0.70..37.66 rows=50 width=24) (actual time=0.023..0.094 > rows=50 loops=1) > Output: process_activity_id, process_instance_id, created > Buffers: shared hit=50 > -> Index Scan using > process_activity_process_instance_id_app_id_created_idx on > public.process_activity pa (cost=0.70..3124.97 rows=4226 width=24) > (actual time=0.022..0.079 *rows=50* loops=1) > Output: process_activity_id, process_instance_id, created > Index Cond: ((pa.process_instance_id = ANY > ('{140117466018927,225820556706970,233008275197305}'::bigint[])) AND > (pa.app_id = '427380312000560'::bigint) AND (pa.created > '1970-01-01 > 00:00:00'::timestamp without time zone)) > Buffers: shared hit=50 > Planning time: 0.167 ms > Execution time: 0.137 ms > (9 rows) > > > Can someone explain > > * Why It is fetching more columns and more rows, incase of inner query ? > * Is there any option to really limit values with INNER JOIN, INNER > query ? If yes, can you please share information on this ? > > Thanks in advance for your time and suggestions. > > Regards, Amar -- Adrian Klaver adrian.klaver@aklaver.com
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