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EXPLAIN(7)		 PostgreSQL 17.5 Documentation		    EXPLAIN(7)

NAME
       EXPLAIN - show the execution plan of a statement

SYNOPSIS
       EXPLAIN [ ( option [, ...] ) ] statement

       where option can	be one of:

	   ANALYZE [ boolean ]
	   VERBOSE [ boolean ]
	   COSTS [ boolean ]
	   SETTINGS [ boolean ]
	   GENERIC_PLAN	[ boolean ]
	   BUFFERS [ boolean ]
	   SERIALIZE [ { NONE |	TEXT | BINARY }	]
	   WAL [ boolean ]
	   TIMING [ boolean ]
	   SUMMARY [ boolean ]
	   MEMORY [ boolean ]
	   FORMAT { TEXT | XML | JSON |	YAML }

DESCRIPTION
       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 cheapest.

       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.

	   Important

	   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, MERGE, CREATE TABLE AS, or EXECUTE
	   statement without letting the command affect	your data, use this
	   approach:

	       BEGIN;
	       EXPLAIN ANALYZE ...;
	       ROLLBACK;

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

       VERBOSE
	   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. The query
	   identifier will also	be displayed if	one has	been computed, see
	   compute_query_id for	more details. This parameter defaults to
	   FALSE.

       COSTS
	   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.

       SETTINGS
	   Include information on configuration	parameters. Specifically,
	   include options affecting query planning with value different from
	   the built-in	default	value. This parameter defaults to FALSE.

       GENERIC_PLAN
	   Allow the statement to contain parameter placeholders like $1, and
	   generate a generic plan that	does not depend	on the values of those
	   parameters. See PREPARE for details about generic plans and the
	   types of statement that support parameters. This parameter cannot
	   be used together with ANALYZE. It defaults to FALSE.

       BUFFERS
	   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, the	number of temp
	   blocks read and written, and	the time spent reading and writing
	   data	file blocks, local blocks and temporary	file blocks (in
	   milliseconds) if track_io_timing is enabled.	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
	   temporary 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 defaults to FALSE.

       SERIALIZE
	   Include information on the cost of serializing the query's output
	   data, that is converting it to text or binary format	to send	to the
	   client. This	can be a significant part of the time required for
	   regular execution of	the query, if the datatype output functions
	   are expensive or if TOASTed values must be fetched from out-of-line
	   storage.  EXPLAIN's default behavior, SERIALIZE NONE, does not
	   perform these conversions. If SERIALIZE TEXT	or SERIALIZE BINARY is
	   specified, the appropriate conversions are performed, and the time
	   spent doing so is measured (unless TIMING OFF is specified).	If the
	   BUFFERS option is also specified, then any buffer accesses involved
	   in the conversions are counted too. In no case, however, will
	   EXPLAIN actually send the resulting data to the client; hence
	   network transmission	costs cannot be	investigated this way.
	   Serialization may only be enabled when ANALYZE is also enabled. If
	   SERIALIZE is	written	without	an argument, TEXT is assumed.

       WAL
	   Include information on WAL record generation. Specifically, include
	   the number of records, number of full page images (fpi) and the
	   amount of WAL generated in bytes. In	text format, only non-zero
	   values are printed. This parameter may only be used when ANALYZE is
	   also	enabled. It defaults to	FALSE.

       TIMING
	   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.

       SUMMARY
	   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.

       MEMORY
	   Include information on memory consumption by	the query planning
	   phase. Specifically,	include	the precise amount of storage used by
	   planner in-memory structures, as well as total memory considering
	   allocation overhead.	This parameter defaults	to FALSE.

       FORMAT
	   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.

       boolean
	   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.

       statement
	   Any SELECT, INSERT, UPDATE, DELETE, MERGE, VALUES, EXECUTE,
	   DECLARE, CREATE TABLE AS, or	CREATE MATERIALIZED VIEW AS statement,
	   whose execution plan	you wish to see.

OUTPUTS
       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 provided.

NOTES
       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 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.

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

	   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:

	   EXPLAIN (FORMAT JSON) SELECT	* FROM foo;
		      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:

	   EXPLAIN (FORMAT YAML) SELECT	* FROM foo WHERE i='4';
		     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:

	   EXPLAIN (COSTS FALSE) SELECT	* FROM foo WHERE i = 4;

		   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 query:

	   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=10.77..10.87 rows=10 width=12)	(actual	time=0.043..0.044 rows=10 loops=1)
	      Group Key: foo
	      Batches: 1  Memory Usage:	24kB
	      ->  Index	Scan using test_pkey on	test  (cost=0.29..10.27	rows=99	width=8) (actual time=0.009..0.025 rows=99 loops=1)
		    Index Cond:	((id > 100) AND	(id < 200))
	    Planning Time: 0.244 ms
	    Execution Time: 0.073 ms
	   (7 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.

       Notice that the previous	example	showed a "custom" plan for the
       specific	parameter values given in EXECUTE. We might also wish to see
       the generic plan	for a parameterized query, which can be	done with
       GENERIC_PLAN:

	   EXPLAIN (GENERIC_PLAN)
	     SELECT sum(bar) FROM test
	       WHERE id	> $1 AND id < $2
	       GROUP BY	foo;

					     QUERY PLAN
	   -------------------------------------------------------------------------------
	    HashAggregate  (cost=26.79..26.89 rows=10 width=12)
	      Group Key: foo
	      ->  Index	Scan using test_pkey on	test  (cost=0.29..24.29	rows=500 width=8)
		    Index Cond:	((id > $1) AND (id < $2))
	   (4 rows)

       In this case the	parser correctly inferred that $1 and $2 should	have
       the same	data type as id, so the	lack of	parameter type information
       from PREPARE was	not a problem. In other	cases it might be necessary to
       explicitly specify types	for the	parameter symbols, which can be	done
       by casting them,	for example:

	   EXPLAIN (GENERIC_PLAN)
	     SELECT sum(bar) FROM test
	       WHERE id	> $1::integer AND id < $2::integer
	       GROUP BY	foo;

COMPATIBILITY
       There is	no EXPLAIN statement defined in	the SQL	standard.

       The following syntax was	used before PostgreSQL version 9.0 and is
       still supported:

	   EXPLAIN [ ANALYZE ] [ VERBOSE ] statement

       Note that in this syntax, the options must be specified in exactly the
       order shown.

SEE ALSO
       ANALYZE(7)

PostgreSQL 17.5			     2025			    EXPLAIN(7)

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