Add used_memory column to pg_autopreped_statement view

Author: knizhnik

doc/src/sgml/autoprepare.sgml

@@ -55,8 +55,8 @@
   <para>
     It is possible to inspect autoprepared queries in the backend using
     <literal>pg_autoprepared_statements</literal> view. It shows original text of the
-    query, types of the extracted parameters (replacing literals) and
-    query execution counter.
+    query, types of the extracted parameters (replacing literals),
+    query execution counter and used memory.
   </para>
 
  </chapter>

src/backend/tcop/postgres.c

@@ -216,8 +216,9 @@ typedef struct
 {
 	AutoprepareStatementKey key;
 	CachedPlanSource* plan;
-	dlist_node		  lru;		  /* double linked list to implement LRU */
-	int64			  exec_count; /* counter of execution of this query */
+	dlist_node		  lru;		   /* double linked list to implement LRU */
+	int64			  exec_count;  /* counter of execution of this query */
+	Size              used_memory; /* memory used by prepared statement */
 }  AutoprepareStatement;
 
 static AutoprepareStatement* autoprepare_stmt;
@@ -255,14 +256,6 @@ static int autoprepare_match_fn(const void *key1, const void *key2, Size keysize
 	return strcmp(ask1->query_string, ask2->query_string);
 }
 
-static Size
-get_memory_context_size(MemoryContext ctx)
-{
-	MemoryContextCounters counters = {0};
-	ctx->methods->stats(ctx, NULL, NULL, &counters);
-	return counters.totalspace;
-}
-
 /*
  * This set returning function reads all the autoprepared statements and
  * returns a set of (name, statement, prepare_time, param_types, from_sql).
@@ -295,13 +288,15 @@ pg_autoprepared_statement(PG_FUNCTION_ARGS)
 	 * build tupdesc for result tuples. This must match the definition of the
 	 * pg_prepared_statements view in system_views.sql
 	 */
-	tupdesc = CreateTemplateTupleDesc(3);
+	tupdesc = CreateTemplateTupleDesc(4);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "statement",
 					   TEXTOID, -1, 0);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "parameter_types",
 					   REGTYPEARRAYOID, -1, 0);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "exec_count",
 					   INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "used_memory",
+					   INT8OID, -1, 0);
 
 	/*
 	 * We put all the tuples into a tuplestore in one scan of the hashtable.
@@ -325,14 +320,15 @@ pg_autoprepared_statement(PG_FUNCTION_ARGS)
 		{
 			if (autoprep_stmt->plan != NULL)
 			{
-				Datum		values[3];
-				bool		nulls[3];
+				Datum		values[4];
+				bool		nulls[4];
 				MemSet(nulls, 0, sizeof(nulls));
 
 				values[0] = CStringGetTextDatum(autoprep_stmt->key.query_string);
 				values[1] = build_regtype_array(autoprep_stmt->key.param_types,
 												autoprep_stmt->key.num_params);
 				values[2] = Int64GetDatum(autoprep_stmt->exec_count);
+				values[3] = Int64GetDatum(autoprep_stmt->used_memory);
 
 				tuplestore_putvalues(tupstore, tupdesc, values, nulls);
 			}
@@ -1597,9 +1593,10 @@ exec_parse_message(const char *query_string,	/* string to execute */
 				{
 					/* Drop invalidated plan: it will be reconstructed later */
 					if (autoprepare_memory_limit)
-						autoprepare_used_memory -= get_memory_context_size(autoprepare_stmt->plan->context);
+						autoprepare_used_memory -= autoprepare_stmt->used_memory;
 					DropCachedPlan(autoprepare_stmt->plan);
 					autoprepare_stmt->plan = NULL;
+					autoprepare_stmt->used_memory = 0;
 				}
 				else
 				{
@@ -1612,6 +1609,7 @@ exec_parse_message(const char *query_string,	/* string to execute */
 				/* Initialize autoprepare hash entry */
 				autoprepare_cached_plans += 1;
 				autoprepare_stmt->plan = NULL;
+				autoprepare_stmt->used_memory = 0;
 				autoprepare_stmt->exec_count = 1;
 
 				/* Copy query text and parameter type info to CacheMemoryContext */
@@ -1629,7 +1627,7 @@ exec_parse_message(const char *query_string,	/* string to execute */
 					if (victim->plan)
 					{
 						if (autoprepare_memory_limit)
-							autoprepare_used_memory -= get_memory_context_size(victim->plan->context);
+							autoprepare_used_memory -= victim->used_memory;
 						DropCachedPlan(victim->plan);
 					}
 					hash_search(autoprepare_hash, victim, HASH_REMOVE, NULL);
@@ -1795,7 +1793,11 @@ exec_parse_message(const char *query_string,	/* string to execute */
 	{
 		SaveCachedPlan(psrc);
 		if (autoprepare_stmt)
+		{
 			autoprepare_stmt->plan = psrc;
+			autoprepare_stmt->used_memory = CachedPlanMemoryUsage(autoprepare_stmt->plan);
+			autoprepare_used_memory += autoprepare_stmt->used_memory;
+		}
 		else
 			/*
 			 * We just save the CachedPlanSource into unnamed_stmt_psrc.

src/backend/utils/cache/plancache.c

@@ -2022,3 +2022,39 @@ ResetPlanCache(void)
 		cexpr->is_valid = false;
 	}
 }
+
+/*
+ * CachedPlanMemUsage: Return memory used by the CachedPlanSource
+ *
+ * Returns the malloced memory used by the two MemoryContexts in
+ * CachedPlanSource and (if available) the MemoryContext in the generic plan.
+ * Does not care for the free memory in those MemoryContexts because it is very
+ * unlikely that it is reused for anythink else anymore and can be considered
+ * dead memory anyway. Also the size of the CachedPlanSource struct is added.
+ *
+ * This function is used only for the pg_prepared_statements view to allow
+ * client applications to monitor memory used by prepared statements and to
+ * selects candidates for eviction in memory contraint environments with
+ * automatic preparation of often called queries.
+ */
+Size
+CachedPlanMemoryUsage(CachedPlanSource *plan)
+{
+	MemoryContextCounters counters;
+	MemoryContext context;
+
+	counters.totalspace = 0;
+
+	context = plan->context;
+	context->methods->stats(context,NULL,NULL,&counters);
+
+	context = plan->query_context;
+	context->methods->stats(context,NULL,NULL,&counters);
+
+	if( plan->gplan ) {
+		context = plan->gplan->context;
+		context->methods->stats(context,NULL,NULL,&counters);
+	}
+
+	return counters.totalspace;
+}

src/include/catalog/pg_proc.dat

@@ -7611,9 +7611,9 @@
 { oid => '4035', descr => 'get the autoprepared statements for this session',
   proname => 'pg_autoprepared_statement', prorows => '1000', proretset => 't',
   provolatile => 's', proparallel => 'r', prorettype => 'record',
-  proargtypes => '', proallargtypes => '{text,_regtype,int8}',
-  proargmodes => '{o,o,o}',
-  proargnames => '{statement,parameter_types,exec_count}',
+  proargtypes => '', proallargtypes => '{text,_regtype,int8,int8}',
+  proargmodes => '{o,o,o,o}',
+  proargnames => '{statement,parameter_types,exec_count,used_memory}',
   prosrc => 'pg_autoprepared_statement' },
 { oid => '2511', descr => 'get the open cursors for this session',
   proname => 'pg_cursor', prorows => '1000', proretset => 't',

src/include/utils/plancache.h

@@ -222,4 +222,6 @@ extern void ReleaseCachedPlan(CachedPlan *plan, bool useResOwner);
 extern CachedExpression *GetCachedExpression(Node *expr);
 extern void FreeCachedExpression(CachedExpression *cexpr);
 
+extern Size CachedPlanMemoryUsage(CachedPlanSource *plansource);
+
 #endif							/* PLANCACHE_H */