diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/auto-explain.sgml | 77 |
1 files changed, 44 insertions, 33 deletions
diff --git a/doc/src/sgml/auto-explain.sgml b/doc/src/sgml/auto-explain.sgml index 334996b0e66..d527208271f 100644 --- a/doc/src/sgml/auto-explain.sgml +++ b/doc/src/sgml/auto-explain.sgml @@ -81,6 +81,8 @@ LOAD 'auto_explain'; When this parameter is on, per-plan-node timing occurs for all statements executed, whether or not they run long enough to actually get logged. This can have an extremely negative impact on performance. + Turning off <varname>auto_explain.log_timing</varname> ameliorates the + performance cost, at the price of obtaining less information. </para> </note> </listitem> @@ -88,16 +90,19 @@ LOAD 'auto_explain'; <varlistentry> <term> - <varname>auto_explain.log_verbose</varname> (<type>boolean</type>) + <varname>auto_explain.log_buffers</varname> (<type>boolean</type>) <indexterm> - <primary><varname>auto_explain.log_verbose</> configuration parameter</primary> + <primary><varname>auto_explain.log_buffers</> configuration parameter</primary> </indexterm> </term> <listitem> <para> - <varname>auto_explain.log_verbose</varname> causes <command>EXPLAIN VERBOSE</> - output, rather than just <command>EXPLAIN</> output, to be printed - when an execution plan is logged. This parameter is off by default. + <varname>auto_explain.log_buffers</varname> controls whether buffer + usage statistics are printed when an execution plan is logged; it's + equivalent to the <literal>BUFFERS</> option of <command>EXPLAIN</>. + This parameter has no effect + unless <varname>auto_explain.log_analyze</varname> is enabled. + This parameter is off by default. Only superusers can change this setting. </para> </listitem> @@ -105,19 +110,24 @@ LOAD 'auto_explain'; <varlistentry> <term> - <varname>auto_explain.log_buffers</varname> (<type>boolean</type>) + <varname>auto_explain.log_timing</varname> (<type>boolean</type>) <indexterm> - <primary><varname>auto_explain.log_buffers</> configuration parameter</primary> + <primary><varname>auto_explain.log_timing</> configuration parameter</primary> </indexterm> </term> <listitem> <para> - <varname>auto_explain.log_buffers</varname> causes <command>EXPLAIN - (ANALYZE, BUFFERS)</> output, rather than just <command>EXPLAIN</> - output, to be printed when an execution plan is logged. This parameter is - off by default. Only superusers can change this setting. This - parameter has no effect unless <varname>auto_explain.log_analyze</> - parameter is set. + <varname>auto_explain.log_timing</varname> controls whether per-node + timing information is printed when an execution plan is logged; it's + equivalent to the <literal>TIMING</> option of <command>EXPLAIN</>. + The overhead of repeatedly reading the system clock can slow down + queries significantly on some systems, so it may be useful to set this + parameter to off when only actual row counts, and not exact times, are + needed. + This parameter has no effect + unless <varname>auto_explain.log_analyze</varname> is enabled. + This parameter is on by default. + Only superusers can change this setting. </para> </listitem> </varlistentry> @@ -133,26 +143,27 @@ LOAD 'auto_explain'; <para> <varname>auto_explain.log_triggers</varname> causes trigger execution statistics to be included when an execution plan is logged. - This parameter is off by default. Only superusers can change this - setting. This parameter has no effect unless - <varname>auto_explain.log_analyze</> parameter is set. + This parameter has no effect + unless <varname>auto_explain.log_analyze</varname> is enabled. + This parameter is off by default. + Only superusers can change this setting. </para> </listitem> </varlistentry> <varlistentry> <term> - <varname>auto_explain.log_format</varname> (<type>enum</type>) + <varname>auto_explain.log_verbose</varname> (<type>boolean</type>) <indexterm> - <primary><varname>auto_explain.log_format</> configuration parameter</primary> + <primary><varname>auto_explain.log_verbose</> configuration parameter</primary> </indexterm> </term> <listitem> <para> - <varname>auto_explain.log_format</varname> selects the - <command>EXPLAIN</> output format to be used. - The allowed values are <literal>text</literal>, <literal>xml</literal>, - <literal>json</literal>, and <literal>yaml</literal>. The default is text. + <varname>auto_explain.log_verbose</varname> controls whether verbose + details are printed when an execution plan is logged; it's + equivalent to the <literal>VERBOSE</> option of <command>EXPLAIN</>. + This parameter is off by default. Only superusers can change this setting. </para> </listitem> @@ -160,25 +171,22 @@ LOAD 'auto_explain'; <varlistentry> <term> - <varname>auto_explain.log_timing</varname> (<type>boolean</type>) + <varname>auto_explain.log_format</varname> (<type>enum</type>) <indexterm> - <primary><varname>auto_explain.log_timing</> configuration parameter</primary> + <primary><varname>auto_explain.log_format</> configuration parameter</primary> </indexterm> </term> <listitem> <para> - <varname>auto_explain.log_timing</varname> causes <command>EXPLAIN - (ANALYZE, TIMING off)</> output, rather than just <command>EXPLAIN (ANALYZE)</> - 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 off when only actual row counts, and not exact times, are needed. - This parameter is only effective when <varname>auto_explain.log_analyze</varname> - is also enabled. This parameter is on by default. + <varname>auto_explain.log_format</varname> selects the + <command>EXPLAIN</> output format to be used. + The allowed values are <literal>text</literal>, <literal>xml</literal>, + <literal>json</literal>, and <literal>yaml</literal>. The default is text. Only superusers can change this setting. </para> </listitem> </varlistentry> - + <varlistentry> <term> <varname>auto_explain.log_nested_statements</varname> (<type>boolean</type>) @@ -198,7 +206,9 @@ LOAD 'auto_explain'; </variablelist> <para> - These parameters must be set in <filename>postgresql.conf</>. + In ordinary usage, these parameters are set + in <filename>postgresql.conf</>, although superusers can alter them + on-the-fly within their own sessions. Typical usage might be: </para> @@ -216,6 +226,7 @@ auto_explain.log_min_duration = '3s' <programlisting> postgres=# LOAD 'auto_explain'; postgres=# SET auto_explain.log_min_duration = 0; +postgres=# SET auto_explain.log_analyze = true; postgres=# SELECT count(*) FROM pg_class, pg_index WHERE oid = indrelid AND indisunique; |