diff options
Diffstat (limited to 'doc/src/sgml/ref/explain.sgml')
| -rw-r--r-- | doc/src/sgml/ref/explain.sgml | 64 |
1 files changed, 53 insertions, 11 deletions
diff --git a/doc/src/sgml/ref/explain.sgml b/doc/src/sgml/ref/explain.sgml index cee2431599e..d3b5c979a29 100644 --- a/doc/src/sgml/ref/explain.sgml +++ b/doc/src/sgml/ref/explain.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/ref/explain.sgml,v 1.44 2008/11/14 10:22:47 petere Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/explain.sgml,v 1.45 2009/07/26 23:34:17 tgl Exp $ PostgreSQL documentation --> @@ -31,6 +31,7 @@ PostgreSQL documentation <refsynopsisdiv> <synopsis> +EXPLAIN [ ( { ANALYZE <replaceable class="parameter">boolean</replaceable> | VERBOSE <replaceable class="parameter">boolean</replaceable> | COSTS <replaceable class="parameter">boolean</replaceable> } [, ...] ) ] <replaceable class="parameter">statement</replaceable> EXPLAIN [ ANALYZE ] [ VERBOSE ] <replaceable class="parameter">statement</replaceable> </synopsis> </refsynopsisdiv> @@ -89,6 +90,14 @@ ROLLBACK; </programlisting> </para> </important> + + <para> + Only the <literal>ANALYZE</literal> and <literal>VERBOSE</literal> options + can be specified, and only in that order, without surrounding the option + list in parentheses. Prior to <productname>PostgreSQL</productname> 8.5, + the unparenthesized syntax was the only one supported. It is expected that + all new options will be supported only in the parenthesized syntax. + </para> </refsect1> <refsect1> @@ -99,7 +108,8 @@ ROLLBACK; <term><literal>ANALYZE</literal></term> <listitem> <para> - Carry out the command and show the actual run times. + Carry out the command and show the actual run times. This + parameter defaults to <command>FALSE</command>. </para> </listitem> </varlistentry> @@ -108,7 +118,33 @@ ROLLBACK; <term><literal>VERBOSE</literal></term> <listitem> <para> - Include the output column list for each node in the plan tree. + Include the output column list for each node in the plan tree. This + parameter defaults to <command>FALSE</command>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><literal>COSTS</literal></term> + <listitem> + <para> + 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 <command>TRUE</command>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><replaceable class="parameter">boolean</replaceable></term> + <listitem> + <para> + Specifies whether the selected option should be turned on or off. + You can write <literal>TRUE</literal>, <literal>ON</>, or + <literal>1</literal> to enable the option, and <literal>FALSE</literal>, + <literal>OFF</>, or <literal>0</literal> to disable it. The + <replaceable class="parameter">boolean</replaceable> value can also + be omitted, in which case <literal>TRUE</literal> is assumed. </para> </listitem> </varlistentry> @@ -150,14 +186,6 @@ ROLLBACK; </para> <para> - Genetic query optimization (<acronym>GEQO</acronym>) randomly tests - execution plans. Therefore, when the number of join relations - exceeds <xref linkend="guc-geqo-threshold"> causing genetic query - optimization to be used, the execution plan is likely to change - each time the statement is executed. - </para> - - <para> In order to measure the run-time cost of each node in the execution plan, the current implementation of <command>EXPLAIN ANALYZE</command> can add considerable profiling overhead to query @@ -202,6 +230,20 @@ EXPLAIN SELECT * FROM foo WHERE i = 4; </para> <para> + Here is the same plan with costs suppressed: + +<programlisting> +EXPLAIN (COSTS FALSE) SELECT * FROM foo WHERE i = 4; + + QUERY PLAN +---------------------------- + Index Scan using fi on foo + Index Cond: (i = 4) +(2 rows) +</programlisting> + </para> + + <para> Here is an example of a query plan for a query using an aggregate function: |