Understand the Query Plan to Optimize Performance with EXPLAIN and ...

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Understand the Query Plan to
Optimize Performance with
EXPLAIN and EXPLAIN ANALYZE
Jeevan Chalke
3rd Dec 2020

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.2
Agenda
• Brief on optimizer/planner
• Paths and Plan
• E...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.3
• Statistics
• ANALYZE table
• Creates different paths
•...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.4
Paths and Plan
• Costs
• cpu_tuple_cost (0.01)
• cpu_ope...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.5
# create table mytab1(a int, b int, c int);
# create tab...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.6
# EXPLAIN select * from mytab1;
QUERY PLAN
-------------...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.7
# EXPLAIN select * from mytab1 where a < 800000;
QUERY P...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.8
# create index myidx1 on mytab1(a);
# EXPLAIN select * f...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.9
• Gives the EXPLAIN plan
• Executes the query; discards ...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.10
# EXPLAIN (ANALYZE) select * from mytab1 where a < 8000...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.11
# set enable_seqscan to on;
# EXPLAIN (ANALYZE) select ...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.12
# EXPLAIN (ANALYZE) select a from mytab1 where a > 8000...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.13
# create index myidx2 on mytab1(c);
# EXPLAIN (COSTS OF...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.14
# EXPLAIN (ANALYZE, SETTINGS, COSTS OFF)
select a, x fr...

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# EXPLAIN (COSTS OFF) select a from mytab1 t1 where a i...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.16
Merge Join Hash Join Nested Loop Join
• Sorts, and then...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.17
# EXPLAIN (ANALYZE, BUFFERS) select * from mytab1 t1 wh...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.18
# set work_mem to '32MB';
# EXPLAIN (ANALYZE, BUFFERS) ...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.19
# EXPLAIN (ANALYZE, TIMING OFF) select * from mytab1 t1...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.20
# create table mytab3(x int, y int);
# insert into myta...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.21
# EXPLAIN (ANALYZE, VERBOSE, SUMMARY OFF) select x from...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.22
# EXPLAIN (ANALYZE, VERBOSE)
select count(*) from mytab...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.23
# EXPLAIN VERBOSE select count(*) from mytab3 t1 group ...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.24
# EXPLAIN (ANALYZE, COSTS OFF) select min(b) from mytab...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.25
# EXPLAIN (ANALYZE, COSTS OFF) select max(a) from mytab...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.26
# create table pagg_tab (a int, b int, c text, d int) p...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.27
# EXPLAIN (ANALYZE, COSTS OFF)
select * from pagg_tab;
...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.28
# EXPLAIN (COSTS OFF) select t1.c, count(*) from pagg_t...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.29
# EXPLAIN (ANALYZE, VERBOSE, COSTS OFF)
select count(*)...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.30
# EXPLAIN (ANALYZE, VERBOSE, WAL, COSTS OFF)
insert int...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.31
Explain and Explain Analyze Options
• ANALYZE [ boolean...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.32
Format
# EXPLAIN (FORMAT JSON, verbose off, analyze,
su...

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.33
• EXPLAIN
• https://www.postgresql.org/docs/13/sql-expl...

Who is EDB?

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.35

© Copyright EnterpriseDB Corporation, 2020. All rights reserved.36

Questions?

Thank You !

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