Some infrastructure changes for the upcoming auto-explain contrib module:

* Refactor explain.c slightly to export a convenient-to-use subroutine
for printing EXPLAIN results.

* Provide hooks for plugins to get control at ExecutorStart and ExecutorEnd
as well as ExecutorRun.

* Add some minimal support for tracking the total runtime of ExecutorRun.
This code won't actually do anything unless a plugin prods it to.

* Change the API of the DefineCustomXXXVariable functions to allow nonzero
"flags" to be specified for a custom GUC variable.  While at it, also make
the "bootstrap" default value for custom GUCs be explicitly specified as a
parameter to these functions.  This is to eliminate confusion over where the
default comes from, as has been expressed in the past by some users of the
custom-variable facility.

* Refactor GUC code a bit to ensure that a custom variable gets initialized to
something valid (like its default value) even if the placeholder value was
invalid.

Author: tglsfdc

src/backend/commands/explain.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.180 2008/10/06 20:29:38 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.181 2008/11/19 01:10:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -224,7 +224,6 @@ ExplainOnePlan(PlannedStmt *plannedstmt, ParamListInfo params,
 	QueryDesc  *queryDesc;
 	instr_time	starttime;
 	double		totaltime = 0;
-	ExplainState *es;
 	StringInfoData buf;
 	int			eflags;
 
@@ -265,17 +264,9 @@ ExplainOnePlan(PlannedStmt *plannedstmt, ParamListInfo params,
 		totaltime += elapsed_time(&starttime);
 	}
 
-	es = (ExplainState *) palloc0(sizeof(ExplainState));
-
-	es->printTList = stmt->verbose;
-	es->printAnalyze = stmt->analyze;
-	es->pstmt = queryDesc->plannedstmt;
-	es->rtable = queryDesc->plannedstmt->rtable;
-
+	/* Create textual dump of plan tree */
 	initStringInfo(&buf);
-	explain_outNode(&buf,
-					queryDesc->plannedstmt->planTree, queryDesc->planstate,
-					NULL, 0, es);
+	ExplainPrintPlan(&buf, queryDesc, stmt->analyze, stmt->verbose);
 
 	/*
 	 * If we ran the command, run any AFTER triggers it queued.  (Note this
@@ -290,7 +281,7 @@ ExplainOnePlan(PlannedStmt *plannedstmt, ParamListInfo params,
 	}
 
 	/* Print info about runtime of triggers */
-	if (es->printAnalyze)
+	if (stmt->analyze)
 	{
 		ResultRelInfo *rInfo;
 		bool		show_relname;
@@ -335,7 +326,34 @@ ExplainOnePlan(PlannedStmt *plannedstmt, ParamListInfo params,
 	do_text_output_multiline(tstate, buf.data);
 
 	pfree(buf.data);
-	pfree(es);
+}
+
+/*
+ * ExplainPrintPlan -
+ *	  convert a QueryDesc's plan tree to text and append it to 'str'
+ *
+ * 'analyze' means to include runtime instrumentation results
+ * 'verbose' means a verbose printout (currently, it shows targetlists)
+ *
+ * NB: will not work on utility statements
+ */
+void
+ExplainPrintPlan(StringInfo str, QueryDesc *queryDesc,
+				 bool analyze, bool verbose)
+{
+	ExplainState	es;
+
+	Assert(queryDesc->plannedstmt != NULL);
+
+	memset(&es, 0, sizeof(es));
+	es.printTList = verbose;
+	es.printAnalyze = analyze;
+	es.pstmt = queryDesc->plannedstmt;
+	es.rtable = queryDesc->plannedstmt->rtable;
+
+	explain_outNode(str,
+					queryDesc->plannedstmt->planTree, queryDesc->planstate,
+					NULL, 0, &es);
 }
 
 /*

src/backend/executor/execMain.c

@@ -26,7 +26,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.317 2008/11/16 17:34:28 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execMain.c,v 1.318 2008/11/19 01:10:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -60,8 +60,10 @@
 #include "utils/tqual.h"
 
 
-/* Hook for plugins to get control in ExecutorRun() */
-ExecutorRun_hook_type ExecutorRun_hook = NULL;
+/* Hooks for plugins to get control in ExecutorStart/Run/End() */
+ExecutorStart_hook_type	ExecutorStart_hook = NULL;
+ExecutorRun_hook_type	ExecutorRun_hook = NULL;
+ExecutorEnd_hook_type	ExecutorEnd_hook = NULL;
 
 typedef struct evalPlanQual
 {
@@ -129,10 +131,24 @@ static void intorel_destroy(DestReceiver *self);
  *
  * NB: the CurrentMemoryContext when this is called will become the parent
  * of the per-query context used for this Executor invocation.
+ *
+ * We provide a function hook variable that lets loadable plugins
+ * get control when ExecutorStart is called.  Such a plugin would
+ * normally call standard_ExecutorStart().
+ *
  * ----------------------------------------------------------------
  */
 void
 ExecutorStart(QueryDesc *queryDesc, int eflags)
+{
+	if (ExecutorStart_hook)
+		(*ExecutorStart_hook) (queryDesc, eflags);
+	else
+		standard_ExecutorStart(queryDesc, eflags);
+}
+
+void
+standard_ExecutorStart(QueryDesc *queryDesc, int eflags)
 {
 	EState	   *estate;
 	MemoryContext oldcontext;
@@ -263,6 +279,10 @@ standard_ExecutorRun(QueryDesc *queryDesc,
 	 */
 	oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);
 
+	/* Allow instrumentation of ExecutorRun overall runtime */
+	if (queryDesc->totaltime)
+		InstrStartNode(queryDesc->totaltime);
+
 	/*
 	 * extract information from the query descriptor and the query feature.
 	 */
@@ -298,6 +318,9 @@ standard_ExecutorRun(QueryDesc *queryDesc,
 	if (sendTuples)
 		(*dest->rShutdown) (dest);
 
+	if (queryDesc->totaltime)
+		InstrStopNode(queryDesc->totaltime, estate->es_processed);
+
 	MemoryContextSwitchTo(oldcontext);
 }
 
@@ -306,10 +329,24 @@ standard_ExecutorRun(QueryDesc *queryDesc,
  *
  *		This routine must be called at the end of execution of any
  *		query plan
+ *
+ *		We provide a function hook variable that lets loadable plugins
+ *		get control when ExecutorEnd is called.  Such a plugin would
+ *		normally call standard_ExecutorEnd().
+ *
  * ----------------------------------------------------------------
  */
 void
 ExecutorEnd(QueryDesc *queryDesc)
+{
+	if (ExecutorEnd_hook)
+		(*ExecutorEnd_hook) (queryDesc);
+	else
+		standard_ExecutorEnd(queryDesc);
+}
+
+void
+standard_ExecutorEnd(QueryDesc *queryDesc)
 {
 	EState	   *estate;
 	MemoryContext oldcontext;
@@ -353,6 +390,7 @@ ExecutorEnd(QueryDesc *queryDesc)
 	queryDesc->tupDesc = NULL;
 	queryDesc->estate = NULL;
 	queryDesc->planstate = NULL;
+	queryDesc->totaltime = NULL;
 }
 
 /* ----------------------------------------------------------------

src/backend/tcop/pquery.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/tcop/pquery.c,v 1.124 2008/08/01 13:16:09 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/tcop/pquery.c,v 1.125 2008/11/19 01:10:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -82,6 +82,7 @@ CreateQueryDesc(PlannedStmt *plannedstmt,
 	qd->tupDesc = NULL;
 	qd->estate = NULL;
 	qd->planstate = NULL;
+	qd->totaltime = NULL;
 
 	return qd;
 }
@@ -110,6 +111,7 @@ CreateUtilityQueryDesc(Node *utilitystmt,
 	qd->tupDesc = NULL;
 	qd->estate = NULL;
 	qd->planstate = NULL;
+	qd->totaltime = NULL;
 
 	return qd;
 }