Report-memory-used-for-planning-a-query-in-EXPLAIN-A.txt

From 1c5bdc574b9ab136ec29a2bd86b43fb484a57345 Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Date: Wed, 12 Jul 2023 14:34:14 +0530
Subject: [PATCH] Report memory used for planning a query in EXPLAIN ANALYZE

The memory used in the CurrentMemoryContext and its children is sampled
before and after calling pg_plan_query() from ExplainOneQuery(). The
difference in the two samples is reported as the memory consumed while
planning the query. This may not account for the memory allocated in
memory contexts which are not children of CurrentMemoryContext. These
contexts are usually other long lived contexts, e.g.
CacheMemoryContext, which are shared by all the queries run in a
session. The consumption in those can not be attributed only to a given
query and hence should not be reported any way.

The memory consumption is reported as "Planning Memory" property in
EXPLAIN ANALYZE output.

Ashutosh Bapat
---
 src/backend/commands/explain.c | 12 ++++++++++--
 src/backend/commands/prepare.c |  5 ++++-
 src/backend/utils/mmgr/mcxt.c  | 19 +++++++++++++++++++
 src/include/commands/explain.h |  3 ++-
 src/include/utils/memutils.h   |  1 +
 5 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index a3f1d53d7a..42fe11b3ce 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -471,6 +471,7 @@ standard_ExplainOneQuery(Query *query, int cursorOptions,
 	MemoryContextCounters mem_counters;
 	MemoryContext planner_ctx = NULL;
 	MemoryContext saved_ctx = NULL;
+	Size		mem_consumed;
 
 	if (es->memory)
 	{
@@ -491,12 +492,14 @@ standard_ExplainOneQuery(Query *query, int cursorOptions,
 	if (es->buffers)
 		bufusage_start = pgBufferUsage;
 	INSTR_TIME_SET_CURRENT(planstart);
+	mem_consumed = MemoryContextMemUsed(CurrentMemoryContext);
 
 	/* plan the query */
 	plan = pg_plan_query(query, queryString, cursorOptions, params);
 
 	INSTR_TIME_SET_CURRENT(planduration);
 	INSTR_TIME_SUBTRACT(planduration, planstart);
+	mem_consumed = MemoryContextMemUsed(CurrentMemoryContext) - mem_consumed;
 
 	if (es->memory)
 	{
@@ -514,7 +517,7 @@ standard_ExplainOneQuery(Query *query, int cursorOptions,
 	/* run it (if needed) and produce output */
 	ExplainOnePlan(plan, into, es, queryString, params, queryEnv,
 				   &planduration, (es->buffers ? &bufusage : NULL),
-				   es->memory ? &mem_counters : NULL);
+				   es->memory ? &mem_counters : NULL, &mem_consumed);
 }
 
 /*
@@ -638,7 +641,8 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 			   const char *queryString, ParamListInfo params,
 			   QueryEnvironment *queryEnv, const instr_time *planduration,
 			   const BufferUsage *bufusage,
-			   const MemoryContextCounters *mem_counters)
+			   const MemoryContextCounters *mem_counters,
+			   const Size *mem_consumed)
 {
 	DestReceiver *dest;
 	QueryDesc  *queryDesc;
@@ -769,6 +773,10 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 		double		plantime = INSTR_TIME_GET_DOUBLE(*planduration);
 
 		ExplainPropertyFloat("Planning Time", "ms", 1000.0 * plantime, 3, es);
+
+		if (mem_consumed)
+			ExplainPropertyUInteger("Planning Memory", "bytes",
+									(uint64) *mem_consumed, es);
 	}
 
 	/* Print info about runtime of triggers */
diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index a93f970a29..e5a49e825e 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -582,6 +582,7 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
 	MemoryContextCounters mem_counters;
 	MemoryContext planner_ctx = NULL;
 	MemoryContext saved_ctx = NULL;
+	Size		mem_consumed;
 
 	if (es->memory)
 	{
@@ -596,6 +597,7 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
 	if (es->buffers)
 		bufusage_start = pgBufferUsage;
 	INSTR_TIME_SET_CURRENT(planstart);
+	mem_consumed = MemoryContextMemUsed(CurrentMemoryContext);
 
 	/* Look it up in the hash table */
 	entry = FetchPreparedStatement(execstmt->name, true);
@@ -632,6 +634,7 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
 
 	INSTR_TIME_SET_CURRENT(planduration);
 	INSTR_TIME_SUBTRACT(planduration, planstart);
+	mem_consumed = MemoryContextMemUsed(CurrentMemoryContext) - mem_consumed;
 
 	if (es->memory)
 	{
@@ -656,7 +659,7 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, IntoClause *into, ExplainState *es,
 		if (pstmt->commandType != CMD_UTILITY)
 			ExplainOnePlan(pstmt, into, es, query_string, paramLI, pstate->p_queryEnv,
 						   &planduration, (es->buffers ? &bufusage : NULL),
-						   es->memory ? &mem_counters : NULL);
+						   es->memory ? &mem_counters : NULL, &mem_consumed);
 		else
 			ExplainOneUtility(pstmt->utilityStmt, into, es, pstate, paramLI);
 
diff --git a/src/backend/utils/mmgr/mcxt.c b/src/backend/utils/mmgr/mcxt.c
index 70d33226cb..e0a119a886 100644
--- a/src/backend/utils/mmgr/mcxt.c
+++ b/src/backend/utils/mmgr/mcxt.c
@@ -865,6 +865,25 @@ MemoryContextStatsDetail(MemoryContext context,
 	}
 }
 
+/*
+ * Compute the memory used in the given context and its children.
+ *
+ * XXX: Instead of this separate function we could modify
+ * MemoryContextStatsDetail() to report used memory and disable printing the
+ * detailed stats.
+ */
+extern Size
+MemoryContextMemUsed(MemoryContext context)
+{
+	MemoryContextCounters grand_totals;
+
+	memset(&grand_totals, 0, sizeof(grand_totals));
+
+	MemoryContextStatsInternal(context, 0, false, 100, &grand_totals, false);
+
+	return grand_totals.totalspace - grand_totals.freespace;
+}
+
 /*
  * MemoryContextStatsInternal
  *		One recursion level for MemoryContextStats
diff --git a/src/include/commands/explain.h b/src/include/commands/explain.h
index aa5872bc15..4fb267afef 100644
--- a/src/include/commands/explain.h
+++ b/src/include/commands/explain.h
@@ -108,7 +108,8 @@ extern void ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into,
 						   ParamListInfo params, QueryEnvironment *queryEnv,
 						   const instr_time *planduration,
 						   const BufferUsage *bufusage,
-						   const MemoryContextCounters *mem_counters);
+						   const MemoryContextCounters *mem_counters,
+						   const Size *mem_consumed);
 
 extern void ExplainPrintPlan(ExplainState *es, QueryDesc *queryDesc);
 extern void ExplainPrintTriggers(ExplainState *es, QueryDesc *queryDesc);
diff --git a/src/include/utils/memutils.h b/src/include/utils/memutils.h
index bf93433b78..9afb0bfb2a 100644
--- a/src/include/utils/memutils.h
+++ b/src/include/utils/memutils.h
@@ -92,6 +92,7 @@ extern void MemoryContextStatsDetail(MemoryContext context,
 									 bool print_to_stderr);
 extern void MemoryContextAllowInCriticalSection(MemoryContext context,
 												bool allow);
+extern Size MemoryContextMemUsed(MemoryContext context);
 
 #ifdef MEMORY_CONTEXT_CHECKING
 extern void MemoryContextCheck(MemoryContext context);
-- 
2.45.2.windows.1