Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) - Mailing list pgsql-performance
From | Adrian Klaver |
---|---|
Subject | Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) |
Date | |
Msg-id | 9d796f65-1c94-eb69-4828-04fe75d62885@aklaver.com Whole thread Raw |
In response to | Re: Explain plan changes - IN CLAUSE ( Passing direct values Vs INNERQuery ) (Amarendra Konda <amar.vijaya@gmail.com>) |
List | pgsql-performance |
On 5/7/20 10:49 AM, Amarendra Konda wrote: > Hi David, > > Thanks for the reply.This has optimized number of rows. Yeah, but your execution time has increased an order of magnitude. Not sure if that is what you want. > > Can you please explain, why it is getting more columns in output, even > though we have asked for only one column ? > > > EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS) SELECT > pa.process_activity_id AS pa_process_activity_id FROM process_activity > pa WHERE pa.app_id = '126502930200650' AND pa.created > '1970-01-01 > 00:00:00' AND EXISTS ( SELECT 1 FROM process_instance pi where > pi.app_id = pa.app_id AND pi.user_id = '137074931866340') ORDER BY > pa.process_instance_id,m.created limit 50; > > QUERY PLAN > > ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > ----------------- > Limit (cost=1.14..37.39 rows=50 width=24) (actual > time=821.283..891.629 rows=50 loops=1) > Output: pa.process_activity_id, pa.process_instance_id, pa.created > Buffers: shared hit=274950 > -> Nested Loop Semi Join (cost=1.14..266660108.78 rows=367790473 > width=24) (actual time=821.282..891.607 rows=50 loops=1) > Output: pa.process_activity_id, pa.process_instance_id, pa.created > Buffers: shared hit=274950 > -> Index Scan using > process_activity_process_instance_id_app_id_created_idx on > public.process_activity pa (cost=0.70..262062725.21 rows=367790473 > width=32) (actual time=821.253..891.517 rows=50 loops=1) > * 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, > m.process_activity_fragments, pa.created, pa.updated, pa.rule_id, > pa.marketing_reply_id, pa.delivered_at, pa.reply_fragments, > pa.status_fragment, pa.internal_meta, pa.interaction_id, > pa.do_not_translate, pa.should_translat > e, pa.in_reply_to* > Index Cond: ((m.app_id = '126502930200650'::bigint) AND > (m.created > '1970-01-01 00:00:00'::timestamp without time zone)) > Buffers: shared hit=274946 > -> Materialize (cost=0.43..2.66 rows=1 width=8) (actual > time=0.001..0.001 rows=1 loops=50) > Output: pi.app_id > Buffers: shared hit=4 > -> 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=0.020..0.020 rows=1 loops=1) > Output: pi.app_id > Index Cond: (pi.user_id = '137074931866340'::bigint) > Filter: (pi.app_id = '126502930200650'::bigint) > Buffers: shared hit=4 > Planning time: 0.297 ms > Execution time: 891.686 ms > (20 rows) > > On Thu, May 7, 2020 at 9:17 PM David G. Johnston > <david.g.johnston@gmail.com <mailto:david.g.johnston@gmail.com>> wrote: > > On Thu, May 7, 2020 at 7:40 AM Adrian Klaver > <adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>> wrote: > > 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): > > > What the OP seems to want is a semi-join: > > (not tested) > > SELECT pa.process_activity_id > FROM process_activity pa WHERE pa.app_id = '427380312000560' AND > pa.created > '1970-01-01 00:00:00' > ANDEXISTS ( > SELECT 1 FROM process_instance pi WHERE pi.app_id = pa.app_id AND > pi.user_id = '317079413683604' > ) > ORDER BY > pa.process_instance_id, > pa.created limit 50; > > I'm unsure exactly how this will impact the plan choice but it > should be an improvement, and in any case more correctly defines > what it is you are looking for. > > David J. > -- Adrian Klaver adrian.klaver@aklaver.com
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