v16-0008-instrumentation-Optimize-ExecProcNodeInstr-instr.patch

From acf427d2935c3964d0916db06d3690b57b47dda4 Mon Sep 17 00:00:00 2001
From: Lukas Fittl <lukas@fittl.com>
Date: Sun, 5 Apr 2026 19:30:56 -0700
Subject: [PATCH v16 08/10] instrumentation: Optimize ExecProcNodeInstr
 instructions by inlining

For most queries, the bulk of the overhead of EXPLAIN ANALYZE happens in
ExecProcNodeInstr when starting/stopping instrumentation for that node.

Previously each ExecProcNodeInstr would check which instrumentation
options are active in the InstrStartNode/InstrStopNode calls, and do the
corresponding work (timers, instrumentation stack, etc.). These
conditionals being checked for each tuple being emitted add up, and cause
non-optimal set of instructions to be generated by the compiler.

Because we already have an existing mechanism to specify a function
pointer when instrumentation is enabled, we can instead create specialized
functions that are tailored to the instrumentation options enabled, and
avoid conditionals on subsequent ExecProcNodeInstr calls. This results in
the overhead for EXPLAIN (ANALYZE, TIMING OFF, BUFFERS OFF) for a stress
test with a large COUNT(*) that does many ExecProcNode calls from ~ 20% on
top of actual runtime to ~ 3%. When using BUFFERS ON the same query goes
from ~ 20% to ~ 10% on top of actual runtime.

Author: Lukas Fittl <lukas@fittl.com>
Reviewed-by: Zsolt Parragi <zsolt.parragi@percona.com>
Discussion: https://www.postgresql.org/message-id/flat/CAP53PkxFP7i7-wy98ZmEJ11edYq-RrPvJoa4kzGhBBjERA4Nyw%40mail.gmail.com#e8dfd018a07d7f8d41565a079d40c564

fix up execprocnode 2
---
 src/backend/executor/execProcnode.c |   2 +-
 src/backend/executor/instrument.c   | 164 +++++++++++++++++++++-------
 src/include/executor/instrument.h   |   3 +-
 3 files changed, 126 insertions(+), 43 deletions(-)

diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index 5ca8d91344b..357175ac2cb 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -465,7 +465,7 @@ ExecProcNodeFirst(PlanState *node)
 	 * have ExecProcNode() directly call the relevant function from now on.
 	 */
 	if (node->instrument)
-		node->ExecProcNode = ExecProcNodeInstr;
+		node->ExecProcNode = InstrNodeSetupExecProcNode(node->instrument);
 	else
 		node->ExecProcNode = node->ExecProcNodeReal;
 
diff --git a/src/backend/executor/instrument.c b/src/backend/executor/instrument.c
index 94d57e3bc40..0a42e800ce9 100644
--- a/src/backend/executor/instrument.c
+++ b/src/backend/executor/instrument.c
@@ -70,19 +70,25 @@ InstrInitOptions(Instrumentation *instr, int instrument_options)
 	instr->need_timer = (instrument_options & INSTRUMENT_TIMER) != 0;
 }
 
-inline void
-InstrStart(Instrumentation *instr)
+static inline void
+InstrStartTimer(Instrumentation *instr)
 {
-	if (instr->need_timer)
-	{
-		if (!INSTR_TIME_IS_ZERO(instr->starttime))
-			elog(ERROR, "InstrStart called twice in a row");
-		else
-			INSTR_TIME_SET_CURRENT_FAST(instr->starttime);
-	}
+	Assert(INSTR_TIME_IS_ZERO(instr->starttime));
 
-	if (instr->need_stack)
-		InstrPushStack(instr);
+	INSTR_TIME_SET_CURRENT_FAST(instr->starttime);
+}
+
+static inline void
+InstrStopTimer(Instrumentation *instr, instr_time *accum_time)
+{
+	instr_time	endtime;
+
+	Assert(!INSTR_TIME_IS_ZERO(instr->starttime));
+
+	INSTR_TIME_SET_CURRENT_FAST(endtime);
+	INSTR_TIME_ACCUM_DIFF(*accum_time, endtime, instr->starttime);
+
+	INSTR_TIME_SET_ZERO(instr->starttime);
 }
 
 /*
@@ -92,18 +98,13 @@ InstrStart(Instrumentation *instr)
 static inline void
 InstrStopCommon(Instrumentation *instr, instr_time *accum_time)
 {
-	instr_time	endtime;
-
 	/* update the time only if the timer was requested */
 	if (instr->need_timer)
 	{
 		if (INSTR_TIME_IS_ZERO(instr->starttime))
 			elog(ERROR, "InstrStop called without start");
 
-		INSTR_TIME_SET_CURRENT_FAST(endtime);
-		INSTR_TIME_ACCUM_DIFF(*accum_time, endtime, instr->starttime);
-
-		INSTR_TIME_SET_ZERO(instr->starttime);
+		InstrStopTimer(instr, accum_time);
 	}
 
 	/* pop the stack, unless InstrStopFinalize previously cleaned up */
@@ -111,6 +112,16 @@ InstrStopCommon(Instrumentation *instr, instr_time *accum_time)
 		InstrPopStack(instr);
 }
 
+void
+InstrStart(Instrumentation *instr)
+{
+	if (instr->need_timer)
+		InstrStartTimer(instr);
+
+	if (instr->need_stack)
+		InstrPushStack(instr);
+}
+
 void
 InstrStop(Instrumentation *instr)
 {
@@ -402,16 +413,15 @@ InstrInitNode(NodeInstrumentation *instr, int instrument_options, bool async_mod
 	instr->async_mode = async_mode;
 }
 
-/* Entry to a plan node */
-inline void
+/* Entry to a plan node. If you modify this, check InstrNodeSetupExecProcNode. */
+void
 InstrStartNode(NodeInstrumentation *instr)
 {
 	InstrStart(&instr->instr);
 }
 
-
-/* Exit from a plan node */
-inline void
+/* Exit from a plan node. If you modify this, check InstrNodeSetupExecProcNode. */
+void
 InstrStopNode(NodeInstrumentation *instr, double nTuples)
 {
 	double		save_tuplecount = instr->tuplecount;
@@ -445,25 +455,6 @@ InstrStopNode(NodeInstrumentation *instr, double nTuples)
 	}
 }
 
-/*
- * ExecProcNode wrapper that performs instrumentation calls.  By keeping
- * this a separate function, we avoid overhead in the normal case where
- * no instrumentation is wanted.
- */
-TupleTableSlot *
-ExecProcNodeInstr(PlanState *node)
-{
-	TupleTableSlot *result;
-
-	InstrStartNode(node->instrument);
-
-	result = node->ExecProcNodeReal(node);
-
-	InstrStopNode(node->instrument, TupIsNull(result) ? 0.0 : 1.0);
-
-	return result;
-}
-
 /* Update tuple count */
 void
 InstrUpdateTupleCount(NodeInstrumentation *instr, double nTuples)
@@ -518,6 +509,97 @@ InstrAggNode(NodeInstrumentation *dst, NodeInstrumentation *add)
 		InstrAccumStack(&dst->instr, &add->instr);
 }
 
+/*
+ * Specialized handling of instrumented ExecProcNode
+ *
+ * These functions are equivalent to running ExecProcNodeReal wrapped in
+ * InstrStartNode and InstrStopNode, but avoid the conditionals in the hot path
+ * by checking the instrumentation options when the ExecProcNode pointer gets
+ * first set, and then using a special-purpose function for each. This results
+ * in a more optimized set of compiled instructions.
+ */
+
+/* Simplified pop: restore saved state instead of re-deriving from array */
+static inline void
+InstrPopStackTo(Instrumentation *prev)
+{
+	Assert(instr_stack.stack_size > 0);
+	Assert(instr_stack.stack_size > 1 ? instr_stack.entries[instr_stack.stack_size - 2] == prev : &instr_top == prev);
+	instr_stack.entries[instr_stack.stack_size - 1]->on_stack = false;
+	instr_stack.stack_size--;
+	instr_stack.current = prev;
+}
+
+static pg_attribute_always_inline TupleTableSlot *
+ExecProcNodeInstr(PlanState *node, bool need_timer, bool need_stack)
+{
+	NodeInstrumentation *instr = node->instrument;
+	Instrumentation *prev = instr_stack.current;
+	TupleTableSlot *result;
+
+	if (need_stack)
+		InstrPushStack(&instr->instr);
+	if (need_timer)
+		InstrStartTimer(&instr->instr);
+
+	result = node->ExecProcNodeReal(node);
+
+	if (need_timer)
+		InstrStopTimer(&instr->instr, &instr->counter);
+	if (need_stack)
+		InstrPopStackTo(prev);
+
+	instr->running = true;
+	if (!TupIsNull(result))
+		instr->tuplecount += 1.0;
+
+	return result;
+}
+
+static TupleTableSlot *
+ExecProcNodeInstrFull(PlanState *node)
+{
+	return ExecProcNodeInstr(node, true, true);
+}
+
+static TupleTableSlot *
+ExecProcNodeInstrRowsStackOnly(PlanState *node)
+{
+	return ExecProcNodeInstr(node, false, true);
+}
+
+static TupleTableSlot *
+ExecProcNodeInstrRowsTimerOnly(PlanState *node)
+{
+	return ExecProcNodeInstr(node, true, false);
+}
+
+static TupleTableSlot *
+ExecProcNodeInstrRowsOnly(PlanState *node)
+{
+	return ExecProcNodeInstr(node, false, false);
+}
+
+/*
+ * Returns an ExecProcNode wrapper that performs instrumentation calls,
+ * tailored to the instrumentation options enabled for the node.
+ */
+ExecProcNodeMtd
+InstrNodeSetupExecProcNode(NodeInstrumentation *instr)
+{
+	bool		need_timer = instr->instr.need_timer;
+	bool		need_stack = instr->instr.need_stack;
+
+	if (need_timer && need_stack)
+		return ExecProcNodeInstrFull;
+	else if (need_stack)
+		return ExecProcNodeInstrRowsStackOnly;
+	else if (need_timer)
+		return ExecProcNodeInstrRowsTimerOnly;
+	else
+		return ExecProcNodeInstrRowsOnly;
+}
+
 /* Trigger instrumentation handling */
 TriggerInstrumentation *
 InstrAllocTrigger(QueryInstrumentation *qinstr, int instrument_options, int n)
diff --git a/src/include/executor/instrument.h b/src/include/executor/instrument.h
index 72df21334ff..bd481afd0de 100644
--- a/src/include/executor/instrument.h
+++ b/src/include/executor/instrument.h
@@ -302,7 +302,8 @@ extern void InstrAggNode(NodeInstrumentation *dst, NodeInstrumentation *add);
 
 typedef struct TupleTableSlot TupleTableSlot;
 typedef struct PlanState PlanState;
-extern TupleTableSlot *ExecProcNodeInstr(PlanState *node);
+typedef TupleTableSlot *(*ExecProcNodeMtd) (PlanState *pstate);
+extern ExecProcNodeMtd InstrNodeSetupExecProcNode(NodeInstrumentation *instr);
 
 extern TriggerInstrumentation *InstrAllocTrigger(QueryInstrumentation *qinstr,
 												 int instrument_options, int n);
-- 
2.47.1