Fix for 'triggered dynamic library load' bug.

This is fix for a very rare case when we don't load aqo as shared library during
startup perform 'CREATE EXTENSION aqo' command in the backend and the first
query in another backend is 'UPDATE aqo_queries...'. In this case AFTER UPDATE trigger
causes AQO _PG_init() routine call. All hooks will be initialized at the end of UPDATE
query execution. Thereby, ExecutorEnd hook will be called without the ExecutorStart.

Author: danolivo

aqo.c

@@ -98,7 +98,6 @@ _PG_init(void)
 	ExplainOnePlan_hook							= print_into_explain;
 
 	init_deactivated_queries_storage();
-
 	AQOMemoryContext = AllocSetContextCreate(TopMemoryContext, "AQOMemoryContext", ALLOCSET_DEFAULT_SIZES);
 }
 

postprocessing.c

@@ -45,7 +45,7 @@ static void update_query_stat_row(double *et, int *et_size,
 					  double cardinality_error,
 					  int64 *n_exec);
 static void StoreToQueryContext(QueryDesc *queryDesc);
-static void ExtractFromQueryContext(QueryDesc *queryDesc);
+static bool ExtractFromQueryContext(QueryDesc *queryDesc);
 static void RemoveFromQueryContext(QueryDesc *queryDesc);
 
 /*
@@ -408,7 +408,8 @@ learn_query_stat(QueryDesc *queryDesc)
 	QueryStat  *stat = NULL;
 	instr_time	endtime;
 
-	ExtractFromQueryContext(queryDesc);
+	if (!ExtractFromQueryContext(queryDesc))
+		goto end;
 
 	if (query_context.explain_only)
 	{
@@ -486,6 +487,7 @@ learn_query_stat(QueryDesc *queryDesc)
 	}
 	RemoveFromQueryContext(queryDesc);
 
+end:
 	if (prev_ExecutorEnd_hook)
 		prev_ExecutorEnd_hook(queryDesc);
 	else
@@ -495,7 +497,6 @@ learn_query_stat(QueryDesc *queryDesc)
 	 * standard_ExecutorEnd clears the queryDesc->planstate. After this point no
 	 * one operation with the plan can be made.
 	 */
-//	ExtractFromQueryContext(queryDesc);
 }
 
 /*
@@ -531,20 +532,27 @@ StoreToQueryContext(QueryDesc *queryDesc)
 /*
  * Restore AQO data, related to the query.
  */
-static void
+static bool
 ExtractFromQueryContext(QueryDesc *queryDesc)
 {
 	EphemeralNamedRelation	enr;
-	int	qcsize = sizeof(QueryContextData);
-	MemoryContext	oldCxt;
 
-	Assert(queryDesc->queryEnv != NULL);
+	/* This is a very rare case when we don't load aqo as shared library during
+	 * startup perform 'CREATE EXTENSION aqo' command in the backend and first
+	 * query in any another backend is 'UPDATE aqo_queries...'. In this case
+	 * ExecutorEnd hook will be executed without ExecutorStart hook.
+	 */
+	if (queryDesc->queryEnv == NULL)
+		return false;
 
-	oldCxt = MemoryContextSwitchTo(AQOMemoryContext);
 	enr = get_ENR(queryDesc->queryEnv, AQOPrivateData);
-	memcpy(&query_context, enr->reldata, qcsize);
 
-	MemoryContextSwitchTo(oldCxt);
+	if (enr == NULL)
+		return false;
+
+	memcpy(&query_context, enr->reldata, sizeof(QueryContextData));
+
+	return true;
 }
 
 static void