sql: add metrics for prepared statement memory usage

Add node-level metrics for memory used by prepared statements across all
sessions.

Assists: #72581

Epic: None

Release note (ui change): Add the following new metrics to track memory
usage of prepared statements in sessions:
- sql.mem.internal.session.prepared.current
- sql.mem.internal.session.prepared.max-avg
- sql.mem.internal.session.prepared.max-count
- sql.mem.internal.session.prepared.max-max
- sql.mem.internal.session.prepared.max-p50
- sql.mem.internal.session.prepared.max-p75
- sql.mem.internal.session.prepared.max-p90
- sql.mem.internal.session.prepared.max-p99
- sql.mem.internal.session.prepared.max-p99.9
- sql.mem.internal.session.prepared.max-p99.99
- sql.mem.internal.session.prepared.max-p99.999
- sql.mem.sql.session.prepared.current
- sql.mem.sql.session.prepared.max-avg
- sql.mem.sql.session.prepared.max-count
- sql.mem.sql.session.prepared.max-max
- sql.mem.sql.session.prepared.max-p50
- sql.mem.sql.session.prepared.max-p75
- sql.mem.sql.session.prepared.max-p90
- sql.mem.sql.session.prepared.max-p99
- sql.mem.sql.session.prepared.max-p99.9
- sql.mem.sql.session.prepared.max-p99.99
- sql.mem.sql.session.prepared.max-p99.999

pkg/sql/conn_executor.go

@@ -958,6 +958,13 @@ func (s *Server) newConnExecutor(
 		memMetrics.SessionMaxBytesHist,
 		-1 /* increment */, noteworthyMemoryUsageBytes, s.cfg.Settings,
 	)
+	sessionPreparedMon := mon.NewMonitor(
+		"session prepared statements",
+		mon.MemoryResource,
+		memMetrics.SessionPreparedCurBytesCount,
+		memMetrics.SessionPreparedMaxBytesHist,
+		-1 /* increment */, noteworthyMemoryUsageBytes, s.cfg.Settings,
+	)
 	// The txn monitor is started in txnState.resetForNewSQLTxn().
 	txnMon := mon.NewMonitor(
 		"txn",
@@ -975,6 +982,7 @@ func (s *Server) newConnExecutor(
 		clientComm:          clientComm,
 		mon:                 sessionRootMon,
 		sessionMon:          sessionMon,
+		sessionPreparedMon:  sessionPreparedMon,
 		sessionDataStack:    sdMutIterator.sds,
 		dataMutatorIterator: sdMutIterator,
 		state: txnState{
@@ -1205,10 +1213,12 @@ func (ex *connExecutor) close(ctx context.Context, closeType closeType) {
 
 	if closeType != panicClose {
 		ex.state.mon.Stop(ctx)
+		ex.sessionPreparedMon.Stop(ctx)
 		ex.sessionMon.Stop(ctx)
 		ex.mon.Stop(ctx)
 	} else {
 		ex.state.mon.EmergencyStop(ctx)
+		ex.sessionPreparedMon.EmergencyStop(ctx)
 		ex.sessionMon.EmergencyStop(ctx)
 		ex.mon.EmergencyStop(ctx)
 	}
@@ -1254,6 +1264,9 @@ type connExecutor struct {
 	// statistics for result sets (which escape transactions).
 	mon        *mon.BytesMonitor
 	sessionMon *mon.BytesMonitor
+
+	// sessionPreparedMon tracks memory usage by prepared statements.
+	sessionPreparedMon *mon.BytesMonitor
 	// memMetrics contains the metrics that statements executed on this connection
 	// will contribute to.
 	memMetrics MemoryMetrics
@@ -1812,6 +1825,7 @@ func (ex *connExecutor) activate(
 	// single threaded, and the point of buffering is just to avoid contention.
 	ex.mon.Start(ctx, parentMon, reserved)
 	ex.sessionMon.StartNoReserved(ctx, ex.mon)
+	ex.sessionPreparedMon.StartNoReserved(ctx, ex.sessionMon)
 
 	// Enable the trace if configured.
 	if traceSessionEventLogEnabled.Get(&ex.server.cfg.Settings.SV) {

pkg/sql/conn_executor_prepare.go

@@ -157,7 +157,7 @@ func (ex *connExecutor) prepare(
 ) (_ *PreparedStatement, retErr error) {
 
 	prepared := &PreparedStatement{
-		memAcc:   ex.sessionMon.MakeBoundAccount(),
+		memAcc:   ex.sessionPreparedMon.MakeBoundAccount(),
 		refCount: 1,
 
 		createdAt: timeutil.Now(),

pkg/sql/mem_metrics.go

@@ -34,6 +34,10 @@ type MemoryMetrics struct {
 	TxnCurBytesCount     *metric.Gauge
 	SessionMaxBytesHist  metric.IHistogram
 	SessionCurBytesCount *metric.Gauge
+
+	// For prepared statements.
+	SessionPreparedMaxBytesHist  metric.IHistogram
+	SessionPreparedCurBytesCount *metric.Gauge
 }
 
 // MetricStruct implements the metrics.Struct interface.
@@ -92,6 +96,8 @@ func MakeMemMetrics(endpoint string, histogramWindow time.Duration) MemoryMetric
 	MetaMemTxnCurBytes := makeMemMetricMetadata(prefix+".txn.current", "Current sql transaction memory usage for "+endpoint)
 	MetaMemMaxSessionBytes := makeMemMetricMetadata(prefix+".session.max", "Memory usage per sql session for "+endpoint)
 	MetaMemSessionCurBytes := makeMemMetricMetadata(prefix+".session.current", "Current sql session memory usage for "+endpoint)
+	MetaMemMaxSessionPreparedBytes := makeMemMetricMetadata(prefix+".session.prepared.max", "Memory usage by prepared statements per sql session for "+endpoint)
+	MetaMemSessionPreparedCurBytes := makeMemMetricMetadata(prefix+".session.prepared.current", "Current sql session memory usage by prepared statements for "+endpoint)
 	return MemoryMetrics{
 		BaseMemoryMetrics: base,
 		TxnMaxBytesHist: metric.NewHistogram(metric.HistogramOptions{
@@ -108,6 +114,12 @@ func MakeMemMetrics(endpoint string, histogramWindow time.Duration) MemoryMetric
 			SigFigs:  3,
 			Buckets:  metric.MemoryUsage64MBBuckets}),
 		SessionCurBytesCount: metric.NewGauge(MetaMemSessionCurBytes),
+		SessionPreparedMaxBytesHist: metric.NewHistogram(metric.HistogramOptions{
+			Metadata: MetaMemMaxSessionPreparedBytes,
+			Duration: histogramWindow,
+			MaxVal:   log10int64times1000,
+			SigFigs:  3,
+			Buckets:  metric.MemoryUsage64MBBuckets}),
+		SessionPreparedCurBytesCount: metric.NewGauge(MetaMemSessionPreparedCurBytes),
 	}
-
 }