Extend EXPLAIN to support output in XML or JSON format.

There are probably still some adjustments to be made in the details
of the output, but this gets the basic structure in place.

Robert Haas

contrib/auto_explain/auto_explain.c

@@ -6,7 +6,7 @@
  * Copyright (c) 2008-2009, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/contrib/auto_explain/auto_explain.c,v 1.6 2009/07/26 23:34:17 tgl Exp $
+ *	  $PostgreSQL: pgsql/contrib/auto_explain/auto_explain.c,v 1.7 2009/08/10 05:46:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -22,8 +22,16 @@ PG_MODULE_MAGIC;
 static int	auto_explain_log_min_duration = -1; /* msec or -1 */
 static bool auto_explain_log_analyze = false;
 static bool auto_explain_log_verbose = false;
+static int	auto_explain_log_format = EXPLAIN_FORMAT_TEXT;
 static bool auto_explain_log_nested_statements = false;
 
+static const struct config_enum_entry format_options[] = {
+        {"text", EXPLAIN_FORMAT_TEXT, false},
+        {"xml", EXPLAIN_FORMAT_XML, false},
+        {"json", EXPLAIN_FORMAT_JSON, false},
+        {NULL, 0, false}
+};
+
 /* Current nesting depth of ExecutorRun calls */
 static int	nesting_level = 0;
 
@@ -84,6 +92,17 @@ _PG_init(void)
 							 NULL,
 							 NULL);
 
+	DefineCustomEnumVariable("auto_explain.log_format",
+							 "EXPLAIN format to be used for plan logging.",
+							 NULL,
+							 &auto_explain_log_format,
+							 EXPLAIN_FORMAT_TEXT,
+							 format_options,
+							 PGC_SUSET,
+							 0,
+							 NULL,
+							 NULL);
+
 	DefineCustomBoolVariable("auto_explain.log_nested_statements",
 							 "Log nested statements.",
 							 NULL,
@@ -201,6 +220,7 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
 			ExplainInitState(&es);
 			es.analyze = (queryDesc->doInstrument && auto_explain_log_analyze);
 			es.verbose = auto_explain_log_verbose;
+			es.format = auto_explain_log_format;
 
 			ExplainPrintPlan(&es, queryDesc);
 

doc/src/sgml/auto-explain.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/auto-explain.sgml,v 1.3 2009/01/02 01:16:02 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/auto-explain.sgml,v 1.4 2009/08/10 05:46:50 tgl Exp $ -->
 
 <sect1 id="auto-explain">
  <title>auto_explain</title>
@@ -102,6 +102,24 @@ LOAD 'auto_explain';
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term>
+     <varname>auto_explain.log_format</varname> (<type>enum</type>)
+    </term>
+    <indexterm>
+     <primary><varname>auto_explain.log_format</> configuration parameter</primary>
+    </indexterm>
+    <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>,
+      and <literal>json</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>)

doc/src/sgml/ref/explain.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/explain.sgml,v 1.45 2009/07/26 23:34:17 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/explain.sgml,v 1.46 2009/08/10 05:46:50 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -31,7 +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 <replaceable class="parameter">boolean</replaceable> | VERBOSE <replaceable class="parameter">boolean</replaceable> | COSTS <replaceable class="parameter">boolean</replaceable> | FORMAT { TEXT | XML | JSON } } [, ...] ) ] <replaceable class="parameter">statement</replaceable>
 EXPLAIN [ ANALYZE ] [ VERBOSE ] <replaceable class="parameter">statement</replaceable>
 </synopsis>
  </refsynopsisdiv>
@@ -109,7 +109,7 @@ ROLLBACK;
     <listitem>
      <para>
       Carry out the command and show the actual run times.  This
-      parameter defaults to <command>FALSE</command>.
+      parameter defaults to <literal>FALSE</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -118,8 +118,12 @@ ROLLBACK;
     <term><literal>VERBOSE</literal></term>
     <listitem>
      <para>
-      Include the output column list for each node in the plan tree.  This
-      parameter defaults to <command>FALSE</command>.
+      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
+      <literal>FALSE</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -130,7 +134,19 @@ ROLLBACK;
      <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>.
+      width of each row.  This parameter defaults to <literal>TRUE</literal>.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>FORMAT</literal></term>
+    <listitem>
+     <para>
+      Specify the output format, which can be TEXT, XML, or JSON.
+      XML or JSON output contains the same information as the text output
+      format, but is easier for programs to parse.  This parameter defaults to
+      <literal>TEXT</literal>.
      </para>
     </listitem>
    </varlistentry>