EXPLAIN

Synopsis

Use the EXPLAIN statement to show the execution plan for an statement. If the ANALYZE option is used, the statement will be executed, rather than just planned. In that case, execution information (rather than just the planner’s estimates) is added to the EXPLAIN result.

Syntax

  1. explain ::= EXPLAIN [ [ ANALYZE ] [ VERBOSE ] | ( option [ , ... ] ) ] 
  2.             statement
  4. option ::= ANALYZE [ boolean ]
  5.            | VERBOSE [ boolean ]
  6.            | COSTS [ boolean ]
  7.            | BUFFERS [ boolean ]
  8.            | TIMING [ boolean ]
  9.            | SUMMARY [ boolean ]
  10.            | FORMAT { TEXT | XML | JSON | YAML }

explain

EXPLAIN - 图1

option

EXPLAIN - 图2

Semantics

Where statement is the target statement (see more here).

ANALYZE

Execute the statement and show actual run times and other statistics.

Examples

Create a sample table.

  1. yugabyte=# CREATE TABLE sample(k1 int, k2 int, v1 int, v2 text, PRIMARY KEY (k1, k2));

Insert some rows.

  1. yugabyte=# INSERT INTO sample(k1, k2, v1, v2) VALUES (1, 2.0, 3, 'a'), (2, 3.0, 4, 'b'), (3, 4.0, 5, 'c');

Check the execution plan for simple select (condition will get pushed down).

  1. yugabyte=# EXPLAIN SELECT * FROM sample WHERE k1 = 1;

  1.                            QUERY PLAN

Foreign Scan on sample (cost=0.00..112.50 rows=1000 width=44)(1 row)

  • Check the execution plan for select with complex condition (second condition requires filtering).
  1. yugabyte=# EXPLAIN SELECT * FROM sample WHERE k1 = 2 and floor(k2 + 1.5) = v1;

  1.                        QUERY PLAN

Foreign Scan on sample (cost=0.00..125.00 rows=1000 width=44)Filter: (floor(((k2)::numeric + 1.5)) = (v1)::numeric)(2 rows)

Check execution with ANALYZE option.

  1. yugabyte=# EXPLAIN ANALYZE SELECT * FROM sample WHERE k1 = 2 and floor(k2 + 1.5) = v1;
  1. ----------------------------------------------------------------------------------------------------------
  2.  Foreign Scan on sample  (cost=0.00..125.00 rows=1000 width=44) (actual time=6.483..6.487 rows=1 loops=1)
  3.    Filter: (floor(((k2)::numeric + 1.5)) = (v1)::numeric)
  4.  Planning time: 2.390 ms
  5.  Execution time: 5.146 ms
  6. (4 rows)

See also