Add EXPLAIN (MEMORY) to report planner memory consumption

This adds a new "Memory:" line under the "Planning:" group (which
currently only has "Buffers:") when the MEMORY option is specified.

In order to make the reporting reasonably accurate, we create a separate
memory context for planner activities, to be used only when this option
is given.  The total amount of memory allocated by that context is
reported as "allocated"; we subtract memory in the context's freelists
from that and report that result as "used".  We use
MemoryContextStatsInternal() to obtain the quantities.

The code structure to show buffer usage during planning was not in
amazing shape, so I (Álvaro) modified the patch a bit to clean that up
in passing.

Author: Ashutosh Bapat
Reviewed-by: David Rowley, Andrey Lepikhov, Jian He, Andy Fan
Discussion: https://www.postgresql.org/message-id/CAExHW5sZA=5LJ_ZPpRO-w09ck8z9p7eaYAqq3Ks9GDfhrxeWBw@mail.gmail.com

Author: alvherre

contrib/auto_explain/auto_explain.c

@@ -396,6 +396,8 @@ explain_ExecutorEnd(QueryDesc *queryDesc)
 			es->wal = (es->analyze && auto_explain_log_wal);
 			es->timing = (es->analyze && auto_explain_log_timing);
 			es->summary = es->analyze;
+			/* No support for MEMORY */
+			/* es->memory = false; */
 			es->format = auto_explain_log_format;
 			es->settings = auto_explain_log_settings;
 

doc/src/sgml/ref/explain.sgml

@@ -44,6 +44,7 @@ EXPLAIN [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] <rep
     WAL [ <replaceable class="parameter">boolean</replaceable> ]
     TIMING [ <replaceable class="parameter">boolean</replaceable> ]
     SUMMARY [ <replaceable class="parameter">boolean</replaceable> ]
+    MEMORY [ <replaceable class="parameter">boolean</replaceable> ]
     FORMAT { TEXT | XML | JSON | YAML }
 </synopsis>
  </refsynopsisdiv>
@@ -250,6 +251,19 @@ ROLLBACK;
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>MEMORY</literal></term>
+    <listitem>
+     <para>
+      Include information on memory consumption by the query planning phase.
+      Specifically, include the precise amount of storage used by planner
+      in-memory structures, as well as total memory considering allocation
+      overhead.
+      This parameter defaults to <literal>FALSE</literal>.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>FORMAT</literal></term>
     <listitem>

src/backend/commands/explain.c

@@ -119,9 +119,11 @@ static void show_instrumentation_count(const char *qlabel, int which,
 static void show_foreignscan_info(ForeignScanState *fsstate, ExplainState *es);
 static void show_eval_params(Bitmapset *bms_params, ExplainState *es);
 static const char *explain_get_index_name(Oid indexId);
-static void show_buffer_usage(ExplainState *es, const BufferUsage *usage,
-							  bool planning);
+static bool peek_buffer_usage(ExplainState *es, const BufferUsage *usage);
+static void show_buffer_usage(ExplainState *es, const BufferUsage *usage);
 static void show_wal_usage(ExplainState *es, const WalUsage *usage);
+static void show_memory_counters(ExplainState *es,
+								 const MemoryContextCounters *mem_counters);
 static void ExplainIndexScanDetails(Oid indexid, ScanDirection indexorderdir,
 									ExplainState *es);
 static void ExplainScanTarget(Scan *plan, ExplainState *es);
@@ -202,6 +204,8 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
 			summary_set = true;
 			es->summary = defGetBoolean(opt);
 		}
+		else if (strcmp(opt->defname, "memory") == 0)
+			es->memory = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "format") == 0)
 		{
 			char	   *p = defGetString(opt);
@@ -397,6 +401,25 @@ ExplainOneQuery(Query *query, int cursorOptions,
 					planduration;
 		BufferUsage bufusage_start,
 					bufusage;
+		MemoryContextCounters mem_counters;
+		MemoryContext planner_ctx = NULL;
+		MemoryContext saved_ctx = NULL;
+
+		if (es->memory)
+		{
+			/*
+			 * Create a new memory context to measure planner's memory
+			 * consumption accurately.  Note that if the planner were to be
+			 * modified to use a different memory context type, here we would
+			 * be changing that to AllocSet, which might be undesirable.
+			 * However, we don't have a way to create a context of the same
+			 * type as another, so we pray and hope that this is OK.
+			 */
+			planner_ctx = AllocSetContextCreate(CurrentMemoryContext,
+												"explain analyze planner context",
+												ALLOCSET_DEFAULT_SIZES);
+			saved_ctx = MemoryContextSwitchTo(planner_ctx);
+		}
 
 		if (es->buffers)
 			bufusage_start = pgBufferUsage;
@@ -408,6 +431,12 @@ ExplainOneQuery(Query *query, int cursorOptions,
 		INSTR_TIME_SET_CURRENT(planduration);
 		INSTR_TIME_SUBTRACT(planduration, planstart);
 
+		if (es->memory)
+		{
+			MemoryContextSwitchTo(saved_ctx);
+			MemoryContextMemConsumed(planner_ctx, &mem_counters);
+		}
+
 		/* calc differences of buffer counters. */
 		if (es->buffers)
 		{
@@ -417,7 +446,8 @@ ExplainOneQuery(Query *query, int cursorOptions,
 
 		/* run it (if needed) and produce output */
 		ExplainOnePlan(plan, into, es, queryString, params, queryEnv,
-					   &planduration, (es->buffers ? &bufusage : NULL));
+					   &planduration, (es->buffers ? &bufusage : NULL),
+					   es->memory ? &mem_counters : NULL);
 	}
 }
 
@@ -527,7 +557,8 @@ void
 ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 			   const char *queryString, ParamListInfo params,
 			   QueryEnvironment *queryEnv, const instr_time *planduration,
-			   const BufferUsage *bufusage)
+			   const BufferUsage *bufusage,
+			   const MemoryContextCounters *mem_counters)
 {
 	DestReceiver *dest;
 	QueryDesc  *queryDesc;
@@ -615,11 +646,27 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 	/* Create textual dump of plan tree */
 	ExplainPrintPlan(es, queryDesc);
 
-	/* Show buffer usage in planning */
-	if (bufusage)
+	/* Show buffer and/or memory usage in planning */
+	if (peek_buffer_usage(es, bufusage) || mem_counters)
 	{
 		ExplainOpenGroup("Planning", "Planning", true, es);
-		show_buffer_usage(es, bufusage, true);
+
+		if (es->format == EXPLAIN_FORMAT_TEXT)
+		{
+			ExplainIndentText(es);
+			appendStringInfoString(es->str, "Planning:\n");
+			es->indent++;
+		}
+
+		if (bufusage)
+			show_buffer_usage(es, bufusage);
+
+		if (mem_counters)
+			show_memory_counters(es, mem_counters);
+
+		if (es->format == EXPLAIN_FORMAT_TEXT)
+			es->indent--;
+
 		ExplainCloseGroup("Planning", "Planning", true, es);
 	}
 
@@ -2106,7 +2153,7 @@ ExplainNode(PlanState *planstate, List *ancestors,
 
 	/* Show buffer/WAL usage */
 	if (es->buffers && planstate->instrument)
-		show_buffer_usage(es, &planstate->instrument->bufusage, false);
+		show_buffer_usage(es, &planstate->instrument->bufusage);
 	if (es->wal && planstate->instrument)
 		show_wal_usage(es, &planstate->instrument->walusage);
 
@@ -2125,7 +2172,7 @@ ExplainNode(PlanState *planstate, List *ancestors,
 
 			ExplainOpenWorker(n, es);
 			if (es->buffers)
-				show_buffer_usage(es, &instrument->bufusage, false);
+				show_buffer_usage(es, &instrument->bufusage);
 			if (es->wal)
 				show_wal_usage(es, &instrument->walusage);
 			ExplainCloseWorker(n, es);
@@ -3545,10 +3592,52 @@ explain_get_index_name(Oid indexId)
 }
 
 /*
- * Show buffer usage details.
+ * Return whether show_buffer_usage would have anything to print, if given
+ * the same 'usage' data.  Note that when the format is anything other than
+ * text, we print even if the counters are all zeroes.
+ */
+static bool
+peek_buffer_usage(ExplainState *es, const BufferUsage *usage)
+{
+	bool		has_shared;
+	bool		has_local;
+	bool		has_temp;
+	bool		has_shared_timing;
+	bool		has_local_timing;
+	bool		has_temp_timing;
+
+	if (usage == NULL)
+		return false;
+
+	if (es->format != EXPLAIN_FORMAT_TEXT)
+		return true;
+
+	has_shared = (usage->shared_blks_hit > 0 ||
+				  usage->shared_blks_read > 0 ||
+				  usage->shared_blks_dirtied > 0 ||
+				  usage->shared_blks_written > 0);
+	has_local = (usage->local_blks_hit > 0 ||
+				 usage->local_blks_read > 0 ||
+				 usage->local_blks_dirtied > 0 ||
+				 usage->local_blks_written > 0);
+	has_temp = (usage->temp_blks_read > 0 ||
+				usage->temp_blks_written > 0);
+	has_shared_timing = (!INSTR_TIME_IS_ZERO(usage->shared_blk_read_time) ||
+						 !INSTR_TIME_IS_ZERO(usage->shared_blk_write_time));
+	has_local_timing = (!INSTR_TIME_IS_ZERO(usage->local_blk_read_time) ||
+						!INSTR_TIME_IS_ZERO(usage->local_blk_write_time));
+	has_temp_timing = (!INSTR_TIME_IS_ZERO(usage->temp_blk_read_time) ||
+					   !INSTR_TIME_IS_ZERO(usage->temp_blk_write_time));
+
+	return has_shared || has_local || has_temp || has_shared_timing ||
+		has_local_timing || has_temp_timing;
+}
+
+/*
+ * Show buffer usage details.  This better be sync with peek_buffer_usage.
  */
 static void
-show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
+show_buffer_usage(ExplainState *es, const BufferUsage *usage)
 {
 	if (es->format == EXPLAIN_FORMAT_TEXT)
 	{
@@ -3568,18 +3657,6 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
 										!INSTR_TIME_IS_ZERO(usage->local_blk_write_time));
 		bool		has_temp_timing = (!INSTR_TIME_IS_ZERO(usage->temp_blk_read_time) ||
 									   !INSTR_TIME_IS_ZERO(usage->temp_blk_write_time));
-		bool		show_planning = (planning && (has_shared ||
-												  has_local || has_temp ||
-												  has_shared_timing ||
-												  has_local_timing ||
-												  has_temp_timing));
-
-		if (show_planning)
-		{
-			ExplainIndentText(es);
-			appendStringInfoString(es->str, "Planning:\n");
-			es->indent++;
-		}
 
 		/* Show only positive counter values. */
 		if (has_shared || has_local || has_temp)
@@ -3678,9 +3755,6 @@ show_buffer_usage(ExplainState *es, const BufferUsage *usage, bool planning)
 			}
 			appendStringInfoChar(es->str, '\n');
 		}
-
-		if (show_planning)
-			es->indent--;
 	}
 	else
 	{
@@ -3766,6 +3840,32 @@ show_wal_usage(ExplainState *es, const WalUsage *usage)
 	}
 }
 
+/*
+ * Show memory usage details.
+ */
+static void
+show_memory_counters(ExplainState *es, const MemoryContextCounters *mem_counters)
+{
+	if (es->format == EXPLAIN_FORMAT_TEXT)
+	{
+		ExplainIndentText(es);
+		appendStringInfo(es->str,
+						 "Memory: used=%lld bytes  allocated=%lld bytes",
+						 (long long) (mem_counters->totalspace - mem_counters->freespace),
+						 (long long) mem_counters->totalspace);
+		appendStringInfoChar(es->str, '\n');
+	}
+	else
+	{
+		ExplainPropertyInteger("Memory Used", "bytes",
+							   mem_counters->totalspace - mem_counters->freespace,
+							   es);
+		ExplainPropertyInteger("Memory Allocated", "bytes",
+							   mem_counters->totalspace, es);
+	}
+}
+
+
 /*
  * Add some additional details about an IndexScan or IndexOnlyScan
  */

src/backend/commands/prepare.c

@@ -583,6 +583,19 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
 	instr_time	planduration;
 	BufferUsage bufusage_start,
 				bufusage;
+	MemoryContextCounters mem_counters;
+	MemoryContext planner_ctx = NULL;
+	MemoryContext saved_ctx = NULL;
+
+	if (es->memory)
+	{
+		/* See ExplainOneQuery about this */
+		Assert(IsA(CurrentMemoryContext, AllocSetContext));
+		planner_ctx = AllocSetContextCreate(CurrentMemoryContext,
+											"explain analyze planner context",
+											ALLOCSET_DEFAULT_SIZES);
+		saved_ctx = MemoryContextSwitchTo(planner_ctx);
+	}
 
 	if (es->buffers)
 		bufusage_start = pgBufferUsage;
@@ -624,6 +637,12 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
 	INSTR_TIME_SET_CURRENT(planduration);
 	INSTR_TIME_SUBTRACT(planduration, planstart);
 
+	if (es->memory)
+	{
+		MemoryContextSwitchTo(saved_ctx);
+		MemoryContextMemConsumed(planner_ctx, &mem_counters);
+	}
+
 	/* calc differences of buffer counters. */
 	if (es->buffers)
 	{
@@ -640,7 +659,8 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
 
 		if (pstmt->commandType != CMD_UTILITY)
 			ExplainOnePlan(pstmt, into, es, query_string, paramLI, queryEnv,
-						   &planduration, (es->buffers ? &bufusage : NULL));
+						   &planduration, (es->buffers ? &bufusage : NULL),
+						   es->memory ? &mem_counters : NULL);
 		else
 			ExplainOneUtility(pstmt->utilityStmt, into, es, query_string,
 							  paramLI, queryEnv);

src/backend/utils/mmgr/mcxt.c

@@ -687,6 +687,19 @@ MemoryContextMemAllocated(MemoryContext context, bool recurse)
 	return total;
 }
 
+/*
+ * Return the memory consumption statistics about the given context and its
+ * children.
+ */
+void
+MemoryContextMemConsumed(MemoryContext context,
+						 MemoryContextCounters *consumed)
+{
+	memset(consumed, 0, sizeof(*consumed));
+
+	MemoryContextStatsInternal(context, 0, false, 0, consumed, false);
+}
+
 /*
  * MemoryContextStats
  *		Print statistics about the named context and all its descendants.

src/include/commands/explain.h

@@ -45,6 +45,7 @@ typedef struct ExplainState
 	bool		wal;			/* print WAL usage */
 	bool		timing;			/* print detailed node timing */
 	bool		summary;		/* print total planning and execution timing */
+	bool		memory;			/* print planner's memory usage information */
 	bool		settings;		/* print modified settings */
 	bool		generic;		/* generate a generic plan */
 	ExplainFormat format;		/* output format */
@@ -92,7 +93,8 @@ extern void ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into,
 						   ExplainState *es, const char *queryString,
 						   ParamListInfo params, QueryEnvironment *queryEnv,
 						   const instr_time *planduration,
-						   const BufferUsage *bufusage);
+						   const BufferUsage *bufusage,
+						   const MemoryContextCounters *mem_counters);
 
 extern void ExplainPrintPlan(ExplainState *es, QueryDesc *queryDesc);
 extern void ExplainPrintTriggers(ExplainState *es, QueryDesc *queryDesc);

src/include/utils/memutils.h

@@ -84,6 +84,8 @@ extern Size GetMemoryChunkSpace(void *pointer);
 extern MemoryContext MemoryContextGetParent(MemoryContext context);
 extern bool MemoryContextIsEmpty(MemoryContext context);
 extern Size MemoryContextMemAllocated(MemoryContext context, bool recurse);
+extern void MemoryContextMemConsumed(MemoryContext context,
+									 MemoryContextCounters *consumed);
 extern void MemoryContextStats(MemoryContext context);
 extern void MemoryContextStatsDetail(MemoryContext context, int max_children,
 									 bool print_to_stderr);