Provided by: postgresql-client-11_11.5-1_amd64 bug


       EXPLAIN - show the execution plan of a statement


       EXPLAIN [ ( option [, ...] ) ] statement
       EXPLAIN [ ANALYZE ] [ VERBOSE ] statement

       where option can be one of:

           ANALYZE [ boolean ]
           VERBOSE [ boolean ]
           COSTS [ boolean ]
           BUFFERS [ boolean ]
           TIMING [ boolean ]
           SUMMARY [ boolean ]
           FORMAT { TEXT | XML | JSON | YAML }


       This command displays the execution plan that the PostgreSQL planner generates for the
       supplied statement. The execution plan shows how the table(s) referenced by the statement
       will be scanned — by plain sequential scan, index scan, etc. — and if multiple tables are
       referenced, what join algorithms will be used to bring together the required rows from
       each input table.

       The most critical part of the display is the estimated statement execution cost, which is
       the planner's guess at how long it will take to run the statement (measured in cost units
       that are arbitrary, but conventionally mean disk page fetches). Actually two numbers are
       shown: the start-up cost before the first row can be returned, and the total cost to
       return all the rows. For most queries the total cost is what matters, but in contexts such
       as a subquery in EXISTS, the planner will choose the smallest start-up cost instead of the
       smallest total cost (since the executor will stop after getting one row, anyway). Also, if
       you limit the number of rows to return with a LIMIT clause, the planner makes an
       appropriate interpolation between the endpoint costs to estimate which plan is really the

       The ANALYZE option causes the statement to be actually executed, not only planned. Then
       actual run time statistics are added to the display, including the total elapsed time
       expended within each plan node (in milliseconds) and the total number of rows it actually
       returned. This is useful for seeing whether the planner's estimates are close to reality.

           Keep in mind that the statement is actually executed when the ANALYZE option is used.
           Although EXPLAIN will discard any output that a SELECT would return, other side
           effects of the statement will happen as usual. If you wish to use EXPLAIN ANALYZE on
           an INSERT, UPDATE, DELETE, CREATE TABLE AS, or EXECUTE statement without letting the
           command affect your data, use this approach:

               EXPLAIN ANALYZE ...;

       Only the ANALYZE and VERBOSE options can be specified, and only in that order, without
       surrounding the option list in parentheses. Prior to PostgreSQL 9.0, the unparenthesized
       syntax was the only one supported. It is expected that all new options will be supported
       only in the parenthesized syntax.


           Carry out the command and show actual run times and other statistics. This parameter
           defaults to FALSE.

           Display additional information regarding the plan. Specifically, include the output
           column list for each node in the plan tree, schema-qualify table and function names,
           always label variables in expressions with their range table alias, and always print
           the name of each trigger for which statistics are displayed. This parameter defaults
           to FALSE.

           Include information on the estimated startup and total cost of each plan node, as well
           as the estimated number of rows and the estimated width of each row. This parameter
           defaults to TRUE.

           Include information on buffer usage. Specifically, include the number of shared blocks
           hit, read, dirtied, and written, the number of local blocks hit, read, dirtied, and
           written, and the number of temp blocks read and written. A hit means that a read was
           avoided because the block was found already in cache when needed. Shared blocks
           contain data from regular tables and indexes; local blocks contain data from temporary
           tables and indexes; while temp blocks contain short-term working data used in sorts,
           hashes, Materialize plan nodes, and similar cases. The number of blocks dirtied
           indicates the number of previously unmodified blocks that were changed by this query;
           while the number of blocks written indicates the number of previously-dirtied blocks
           evicted from cache by this backend during query processing. The number of blocks shown
           for an upper-level node includes those used by all its child nodes. In text format,
           only non-zero values are printed. This parameter may only be used when ANALYZE is also
           enabled. It defaults to FALSE.

           Include actual startup time and time spent in each node in the output. The overhead of
           repeatedly reading the system clock can slow down the query significantly on some
           systems, so it may be useful to set this parameter to FALSE when only actual row
           counts, and not exact times, are needed. Run time of the entire statement is always
           measured, even when node-level timing is turned off with this option. This parameter
           may only be used when ANALYZE is also enabled. It defaults to TRUE.

           Include summary information (e.g., totaled timing information) after the query plan.
           Summary information is included by default when ANALYZE is used but otherwise is not
           included by default, but can be enabled using this option. Planning time in EXPLAIN
           EXECUTE includes the time required to fetch the plan from the cache and the time
           required for re-planning, if necessary.

           Specify the output format, which can be TEXT, XML, JSON, or YAML. Non-text output
           contains the same information as the text output format, but is easier for programs to
           parse. This parameter defaults to TEXT.

           Specifies whether the selected option should be turned on or off. You can write TRUE,
           ON, or 1 to enable the option, and FALSE, OFF, or 0 to disable it. The boolean value
           can also be omitted, in which case TRUE is assumed.

           CREATE MATERIALIZED VIEW AS statement, whose execution plan you wish to see.


       The command's result is a textual description of the plan selected for the statement,
       optionally annotated with execution statistics.  Section 14.1 describes the information


       In order to allow the PostgreSQL query planner to make reasonably informed decisions when
       optimizing queries, the pg_statistic data should be up-to-date for all tables used in the
       query. Normally the autovacuum daemon will take care of that automatically. But if a table
       has recently had substantial changes in its contents, you might need to do a manual
       ANALYZE(7) rather than wait for autovacuum to catch up with the changes.

       In order to measure the run-time cost of each node in the execution plan, the current
       implementation of EXPLAIN ANALYZE adds profiling overhead to query execution. As a result,
       running EXPLAIN ANALYZE on a query can sometimes take significantly longer than executing
       the query normally. The amount of overhead depends on the nature of the query, as well as
       the platform being used. The worst case occurs for plan nodes that in themselves require
       very little time per execution, and on machines that have relatively slow operating system
       calls for obtaining the time of day.


       To show the plan for a simple query on a table with a single integer column and 10000

           EXPLAIN SELECT * FROM foo;

                                  QUERY PLAN
            Seq Scan on foo  (cost=0.00..155.00 rows=10000 width=4)
           (1 row)

       Here is the same query, with JSON output formatting:

                      QUERY PLAN
            [                             +
              {                           +
                "Plan": {                 +
                  "Node Type": "Seq Scan",+
                  "Relation Name": "foo", +
                  "Alias": "foo",         +
                  "Startup Cost": 0.00,   +
                  "Total Cost": 155.00,   +
                  "Plan Rows": 10000,     +
                  "Plan Width": 4         +
                }                         +
              }                           +
           (1 row)

       If there is an index and we use a query with an indexable WHERE condition, EXPLAIN might
       show a different plan:

           EXPLAIN SELECT * FROM foo WHERE i = 4;

                                    QUERY PLAN
            Index Scan using fi on foo  (cost=0.00..5.98 rows=1 width=4)
              Index Cond: (i = 4)
           (2 rows)

       Here is the same query, but in YAML format:

                     QUERY PLAN
            - Plan:                      +
                Node Type: "Index Scan"  +
                Scan Direction: "Forward"+
                Index Name: "fi"         +
                Relation Name: "foo"     +
                Alias: "foo"             +
                Startup Cost: 0.00       +
                Total Cost: 5.98         +
                Plan Rows: 1             +
                Plan Width: 4            +
                Index Cond: "(i = 4)"
           (1 row)

       XML format is left as an exercise for the reader.

       Here is the same plan with cost estimates suppressed:


                   QUERY PLAN
            Index Scan using fi on foo
              Index Cond: (i = 4)
           (2 rows)

       Here is an example of a query plan for a query using an aggregate function:

           EXPLAIN SELECT sum(i) FROM foo WHERE i < 10;

                                        QUERY PLAN
            Aggregate  (cost=23.93..23.93 rows=1 width=4)
              ->  Index Scan using fi on foo  (cost=0.00..23.92 rows=6 width=4)
                    Index Cond: (i < 10)
           (3 rows)

       Here is an example of using EXPLAIN EXECUTE to display the execution plan for a prepared

           PREPARE query(int, int) AS SELECT sum(bar) FROM test
               WHERE id > $1 AND id < $2
               GROUP BY foo;

           EXPLAIN ANALYZE EXECUTE query(100, 200);

                                                                  QUERY PLAN
            HashAggregate  (cost=9.54..9.54 rows=1 width=8) (actual time=0.156..0.161 rows=11 loops=1)
              Group Key: foo
              ->  Index Scan using test_pkey on test  (cost=0.29..9.29 rows=50 width=8) (actual time=0.039..0.091 rows=99 loops=1)
                    Index Cond: ((id > $1) AND (id < $2))
            Planning time: 0.197 ms
            Execution time: 0.225 ms
           (6 rows)

       Of course, the specific numbers shown here depend on the actual contents of the tables
       involved. Also note that the numbers, and even the selected query strategy, might vary
       between PostgreSQL releases due to planner improvements. In addition, the ANALYZE command
       uses random sampling to estimate data statistics; therefore, it is possible for cost
       estimates to change after a fresh run of ANALYZE, even if the actual distribution of data
       in the table has not changed.


       There is no EXPLAIN statement defined in the SQL standard.