Re: Join for the parent table will not leverage the index scan

Any help on this would be really helpful.

On Fri, 13 Aug, 2021, 5:53 pm Shrikant Bhende, <shrikantpostgresql(at)gmail(dot)com>
wrote:

>
> We have two tables, both have ~36 partitions.
> This is my first query, which attempts to join the parent tables on the
> columns that have been used to create multi-column indexes for all
> partitions (multi-column indexes defined on session_id, detail_id in that
> order):
>
>
> *PostgreSQL version : 10*-- *query*
>
> explain
>
> select * from dm_ci360.page_details pd
> inner join dm_ci360.page_details_ext pde
> on (pd.session_id = pde.session_id
> and pd.detail_id = pde.detail_id)
> where pd.session_dt >= now()::date-2;
>
> -- *plan*
>
> Hash Join (cost=36927955.75..100106605.07 rows=11 width=8355)
>
> Hash Cond: (((pd.session_id)::text = (pde.session_id)::text) AND
> ((pd.detail_id)::text = (pde.detail_id)::text))
>
> -> Append (cost=1297.33..571870.20 rows=630535 width=8130)
>
> -> Bitmap Heap Scan on page_details_null pd
> (cost=1297.33..240207.85 rows=69259 width=8220)
>
> Recheck Cond: (session_dt >= ((now())::date - 2))
>
> -> Bitmap Index Scan on page_details_null_session_dt_idx
> (cost=0.00..1280.02 rows=69259 width=0)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m3_session_dt_idx on
> page_details_m3 pd_1 (cost=0.44..4.71 rows=1 width=8216)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m2_session_dt_idx on
> page_details_m2 pd_2 (cost=0.43..102.79 rows=621 width=8253)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m1_session_dt_idx on
> page_details_m1 pd_3 (cost=0.44..4.55 rows=1 width=8281)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_5_session_dt_idx on
> page_details_5 pd_4 (cost=0.57..51622.53 rows=196574 width=8202)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Bitmap Heap Scan on page_details_31 pd_5
> (cost=982.61..194857.98 rows=52391 width=7721)
>
> Recheck Cond: (session_dt >= ((now())::date - 2))
>
> -> Bitmap Index Scan on page_details_31_session_dt_idx1
> (cost=0.00..969.51 rows=52391 width=0)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_49_session_dt_idx on
> page_details_49 pd_6 (cost=0.45..10991.08 rows=50039 width=7721)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_52_session_dt_idx on
> page_details_52 pd_7 (cost=0.44..2337.94 rows=10222 width=8297)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_59_session_dt_idx on
> page_details_59 pd_8 (cost=0.57..24790.17 rows=50148 width=8276)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_60_session_dt_idx on
> page_details_60 pd_9 (cost=0.44..7292.41 rows=4259 width=8263)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_61_session_dt_idx on
> page_details_61 pd_10 (cost=0.43..309.10 rows=704 width=8182)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_63_session_dt_idx on
> page_details_63 pd_11 (cost=0.43..13.20 rows=25 width=8250)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_64_session_dt_idx on
> page_details_64 pd_12 (cost=0.44..5.41 rows=1 width=8314)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_66_session_dt_idx on
> page_details_66 pd_13 (cost=0.42..4.49 rows=1 width=8277)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_67_session_dt_idx on
> page_details_67 pd_14 (cost=0.42..58.62 rows=325 width=8227)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_68_session_dt_idx on
> page_details_68 pd_15 (cost=0.42..35.20 rows=111 width=8259)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_78_session_dt_idx on
> page_details_78 pd_16 (cost=0.44..1738.10 rows=4608 width=8263)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_98_session_dt_idx on
> page_details_98 pd_17 (cost=0.44..2157.31 rows=7136 width=8225)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_101_session_dt_idx on
> page_details_101 pd_18 (cost=0.44..2956.03 rows=9241 width=8205)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_130_session_dt_idx on
> page_details_130 pd_19 (cost=0.44..1683.53 rows=19656 width=8199)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m100_session_dt_idx on
> page_details_m100 pd_20 (cost=0.43..4.96 rows=1 width=8225)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m4_session_dt_idx on
> page_details_m4 pd_21 (cost=0.43..659.89 rows=6097 width=8195)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_134_session_dt_idx on
> page_details_134 pd_22 (cost=0.45..4666.25 rows=50409 width=8176)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_58_session_dt_idx on
> page_details_58 pd_23 (cost=0.43..7.05 rows=1 width=8362)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_69_session_dt_idx on
> page_details_69 pd_24 (cost=0.43..125.03 rows=348 width=8268)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_100_session_dt_idx on
> page_details_100 pd_25 (cost=0.43..381.13 rows=466 width=8195)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_114_session_dt_idx on
> page_details_114 pd_26 (cost=0.43..7.80 rows=1 width=8183)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m5_session_dt_idx on
> page_details_m5 pd_27 (cost=0.57..4505.18 rows=50872 width=8225)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_32_session_dt_idx on
> page_details_32 pd_28 (cost=0.43..8.44 rows=1 width=8807)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_23_session_dt_idx on
> page_details_23 pd_29 (cost=0.29..7.47 rows=1 width=9327)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m6_session_dt_idx on
> page_details_m6 pd_30 (cost=0.44..769.32 rows=7135 width=7814)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m7_session_dt_idx on
> page_details_m7 pd_31 (cost=0.44..11400.50 rows=14694 width=8203)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_m8_session_dt_idx on
> page_details_m8 pd_32 (cost=0.44..6568.86 rows=8045 width=8200)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_144_session_dt_idx on
> page_details_144 pd_33 (cost=0.29..21.16 rows=162 width=8189)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_143_session_dt_idx on
> page_details_143 pd_34 (cost=0.43..1477.00 rows=16135 width=8197)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_145_session_dt_idx on
> page_details_145 pd_35 (cost=0.29..87.17 rows=844 width=8226)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Hash (cost=16117516.77..16117516.77 rows=449927377 width=226)
>
> -> Append (cost=0.00..16117516.77 rows=449927377 width=226)
>
> -> Seq Scan on page_details_ext_null pde
> (cost=0.00..1467668.52 rows=40845752 width=226)
>
> -> Seq Scan on page_details_ext_m3 pde_1
> (cost=0.00..347732.32 rows=9980132 width=226)
>
> -> Seq Scan on page_details_ext_m2 pde_2
> (cost=0.00..26146.27 rows=715527 width=226)
>
> -> Seq Scan on page_details_ext_m1 pde_3
> (cost=0.00..180093.08 rows=4793908 width=226)
>
> -> Seq Scan on page_details_ext_5 pde_4
> (cost=0.00..3056150.08 rows=82652608 width=226)
>
> -> Seq Scan on page_details_ext_31 pde_5
> (cost=0.00..4177416.08 rows=124953208 width=226)
>
> -> Seq Scan on page_details_ext_49 pde_6
> (cost=0.00..1034364.84 rows=28538484 width=226)
>
> -> Seq Scan on page_details_ext_52 pde_7
> (cost=0.00..575529.72 rows=16018272 width=226)
>
> -> Seq Scan on page_details_ext_59 pde_8
> (cost=0.00..1226617.78 rows=33054378 width=226)
>
> -> Seq Scan on page_details_ext_60 pde_9
> (cost=0.00..206925.60 rows=5920260 width=226)
>
> -> Seq Scan on page_details_ext_61 pde_10
> (cost=0.00..10599.63 rows=296463 width=226)
>
> -> Seq Scan on page_details_ext_63 pde_11
> (cost=0.00..32993.45 rows=898145 width=226)
>
> -> Seq Scan on page_details_ext_64 pde_12
> (cost=0.00..211220.00 rows=6212500 width=226)
>
> -> Seq Scan on page_details_ext_66 pde_13
> (cost=0.00..4888.44 rows=127544 width=226)
>
> -> Seq Scan on page_details_ext_67 pde_14
> (cost=0.00..5121.02 rows=135402 width=226)
>
> -> Seq Scan on page_details_ext_68 pde_15
> (cost=0.00..4284.18 rows=116218 width=226)
>
> -> Seq Scan on page_details_ext_78 pde_16
> (cost=0.00..135663.64 rows=3705564 width=226)
>
> -> Seq Scan on page_details_ext_98 pde_17
> (cost=0.00..232421.44 rows=6556944 width=226)
>
> -> Seq Scan on page_details_ext_101 pde_18
> (cost=0.00..189844.81 rows=5231481 width=226)
>
> -> Seq Scan on page_details_ext_130 pde_19
> (cost=0.00..318011.40 rows=8558640 width=226)
>
> -> Seq Scan on page_details_ext_m100 pde_20
> (cost=0.00..4914.04 rows=143504 width=226)
>
> -> Seq Scan on page_details_ext_m4 pde_21
> (cost=0.00..75878.68 rows=1994468 width=226)
>
> -> Seq Scan on page_details_ext_134 pde_22
> (cost=0.00..724264.36 rows=19192136 width=226)
>
> -> Seq Scan on page_details_ext_58 pde_23
> (cost=0.00..12171.94 rows=361394 width=331)
>
> -> Seq Scan on page_details_ext_69 pde_24
> (cost=0.00..6464.95 rows=173295 width=226)
>
> -> Seq Scan on page_details_ext_100 pde_25
> (cost=0.00..9217.39 rows=255239 width=226)
>
> -> Seq Scan on page_details_ext_114 pde_26
> (cost=0.00..11702.69 rows=358469 width=226)
>
> -> Seq Scan on page_details_ext_m5 pde_27
> (cost=0.00..1274434.84 rows=33330284 width=226)
>
> -> Seq Scan on page_details_ext_23 pde_28
> (cost=0.00..822.03 rows=25503 width=378)
>
> -> Seq Scan on page_details_ext_32 pde_29
> (cost=0.00..7011.56 rows=217756 width=378)
>
> -> Seq Scan on page_details_ext_m6 pde_30
> (cost=0.00..177039.58 rows=4616658 width=226)
>
> -> Seq Scan on page_details_ext_m7 pde_31
> (cost=0.00..188264.43 rows=5143643 width=226)
>
> -> Seq Scan on page_details_ext_m8 pde_32
> (cost=0.00..139185.56 rows=3799056 width=226)
>
> -> Seq Scan on page_details_ext_144 pde_33
> (cost=0.00..687.46 rows=16246 width=226)
>
> -> Seq Scan on page_details_ext_143 pde_34
> (cost=0.00..41053.82 rows=971482 width=226)
>
> -> Seq Scan on page_details_ext_145 pde_35
> (cost=0.00..711.14 rows=16814 width=226)
>
>
>
> The only place an index scan is used is to filter down page_details. In my
> second query,
> when explicitly joining single partitions an index scan is used to perform
> filtering, and the join as well:
>
> --*query*
>
> explain
>
> select * from dm_ci360.page_details_5 pd
> inner join dm_ci360.page_details_ext_5 pde
> on (pd.session_id = pde.session_id
> and pd.detail_id = pde.detail_id)
> where pd.session_dt >= now()::date-2;
>
>
> --*plan*
>
> Nested Loop (cost=1.27..1685980.38 rows=1 width=8428)
>
> -> Index Scan using page_details_5_session_dt_idx on page_details_5 pd
> (cost=0.57..51267.67 rows=196574 width=8202)
>
> Index Cond: (session_dt >= ((now())::date - 2))
>
> -> Index Scan using page_details_ext_5_session_id_detail_id_idx on
> page_details_ext_5 pde (cost=0.69..8.31 rows=1 width=226)
>
> Index Cond: (((session_id)::text = (pd.session_id)::text) AND
> ((detail_id)::text = (pd.detail_id)::text))
>
> I just cannot figure out why the join for the parent table will not
> leverage the index,
> but the join for a single partition will. We are running on Postgres 10,
> and the row counts for the tables can be found below:
>
> *Row Count*
> page_details -> ~413M
> page_details_ext -> ~450M
>
> *Table DDL*
>
> -- page_detailsCREATE TABLE dm_ci360.page_details ( dml_id int4 NULL, dml_ts timestamp NULL, dml_ts_utc timestamp NULL, dml_type varchar(1) NULL, dwh_job_id int4 NULL, ins_dwh_job_id int4 NULL, upd_dwh_job_id int4 NULL, deleted_flag varchar(1) NULL, processed_dttm timestamp NULL, valid_from_dttm timestamp(0) NULL, valid_to_dttm timestamp(0) NULL, ccd varchar(2000) NULL, client_id int4 NULL, detail_id varchar(32) NULL, session_id varchar(29) NULL, visit_id varchar(32) NULL, window_size_txt varchar(20) NULL, session_dt date NULL, page_url_txt varchar(1332) NULL, domain_nm varchar(165) NULL, bytes_sent_cnt int4 NULL, page_load_sec_cnt int8 NULL, page_complete_sec_cnt int8 NULL, protocol_nm varchar(8) NULL, page_desc varchar(1332) NULL, class1_id varchar(650) NULL, class2_id varchar(650) NULL, class3_id varchar(650) NULL, class4_id varchar(650) NULL, class5_id varchar(650) NULL, class6_id varchar(650) NULL, class7_id varchar(650) NULL, class8_id varchar(650) NULL, class9_id varchar(650) NULL, class10_id varchar(650) NULL, class11_id varchar(650) NULL, class12_id varchar(650) NULL, class13_id varchar(650) NULL, class14_id varchar(650) NULL, class15_id varchar(650) NULL, url_domain varchar(215) NULL, identity_id varchar(36) NULL, detail_dttm timestamp NULL, detail_dttm_tz timestamp NULL, load_dttm timestamp NULL, session_dt_tz date NULL, detail_id_hex varchar(32) NULL, visit_id_hex varchar(32) NULL, session_id_hex varchar(29) NULL)PARTITION BY LIST (client_id);CREATE TABLE dm_ci360.page_details_100 PARTITION OF dm_ci360.page_details FOR VALUES IN (100);CREATE INDEX page_details_100_detail_dttm_idx ON dm_ci360.page_details_100 USING btree (detail_dttm)CREATE INDEX page_details_100_identity_id_idx ON dm_ci360.page_details_100 USING btree (identity_id)CREATE INDEX page_details_100_session_dt_idx ON dm_ci360.page_details_100 USING btree (session_dt)CREATE INDEX page_details_100_session_id_detail_id_idx ON dm_ci360.page_details_100 USING btree (session_id, detail_id)-- page_details_extCREATE TABLE dm_ci360.page_details_ext ( dml_id int4 NULL, dml_ts timestamp NULL, dml_ts_utc timestamp NULL, dml_type varchar(1) NULL, dwh_job_id int4 NULL, ins_dwh_job_id int4 NULL, upd_dwh_job_id int4 NULL, deleted_flag varchar(1) NULL, processed_dttm timestamp NULL, valid_from_dttm timestamp(0) NULL, valid_to_dttm timestamp(0) NULL, ccd varchar(2000) NULL, client_id int4 NULL, detail_id varchar(32) NULL, session_id varchar(29) NULL, active_sec_spent_on_page_cnt int4 NULL, seconds_spent_on_page_cnt int4 NULL, load_dttm timestamp NULL, detail_id_hex varchar(32) NULL, session_id_hex varchar(29) NULL)PARTITION BY LIST (client_id);CREATE TABLE dm_ci360.page_details_ext_100 PARTITION OF dm_ci360.page_details_ext FOR VALUES IN (100);CREATE INDEX page_details_ext_100_session_id_detail_id_idx ON dm_ci360.page_details_ext_100 USING btree (session_id, detail_id)
>
> CREATE INDEX page_details_ext_100_session_id_detail_id_idx ON
> dm_ci360.page_details_ext_100 USING btree (session_id, detail_id)
>
>
> Thanks
>