balancer/rls: Add cache metrics (#7495)

balancer/rls/balancer.go

@@ -79,6 +79,20 @@ var (
 	dataCachePurgeHook   = func() {}
 	resetBackoffHook     = func() {}
 
+	cacheEntriesMetric = estats.RegisterInt64Gauge(estats.MetricDescriptor{
+		Name:        "grpc.lb.rls.cache_entries",
+		Description: "EXPERIMENTAL. Number of entries in the RLS cache.",
+		Unit:        "entry",
+		Labels:      []string{"grpc.target", "grpc.lb.rls.server_target", "grpc.lb.rls.instance_uuid"},
+		Default:     false,
+	})
+	cacheSizeMetric = estats.RegisterInt64Gauge(estats.MetricDescriptor{
+		Name:        "grpc.lb.rls.cache_size",
+		Description: "EXPERIMENTAL. The current size of the RLS cache.",
+		Unit:        "By",
+		Labels:      []string{"grpc.target", "grpc.lb.rls.server_target", "grpc.lb.rls.instance_uuid"},
+		Default:     false,
+	})
 	defaultTargetPicksMetric = estats.RegisterInt64Count(estats.MetricDescriptor{
 		Name:        "grpc.lb.rls.default_target_picks",
 		Description: "EXPERIMENTAL. Number of LB picks sent to the default target.",
@@ -126,7 +140,7 @@ func (rlsBB) Build(cc balancer.ClientConn, opts balancer.BuildOptions) balancer.
 		updateCh:           buffer.NewUnbounded(),
 	}
 	lb.logger = internalgrpclog.NewPrefixLogger(logger, fmt.Sprintf("[rls-experimental-lb %p] ", lb))
-	lb.dataCache = newDataCache(maxCacheSize, lb.logger)
+	lb.dataCache = newDataCache(maxCacheSize, lb.logger, opts.MetricsRecorder, opts.Target.String())
 	lb.bg = balancergroup.New(balancergroup.Options{
 		CC:                      cc,
 		BuildOpts:               opts,
@@ -317,18 +331,17 @@ func (b *rlsBalancer) UpdateClientConnState(ccs balancer.ClientConnState) error
 	b.stateMu.Unlock()
 	<-done
 
+	// We cannot do cache operations above because `cacheMu` needs to be grabbed
+	// before `stateMu` if we are to hold both locks at the same time.
+	b.cacheMu.Lock()
+	b.dataCache.updateRLSServerTarget(newCfg.lookupService)
 	if resizeCache {
 		// If the new config changes reduces the size of the data cache, we
 		// might have to evict entries to get the cache size down to the newly
 		// specified size.
-		//
-		// And we cannot do this operation above (where we compute the
-		// `resizeCache` boolean) because `cacheMu` needs to be grabbed before
-		// `stateMu` if we are to hold both locks at the same time.
-		b.cacheMu.Lock()
 		b.dataCache.resize(newCfg.cacheSizeBytes)
-		b.cacheMu.Unlock()
 	}
+	b.cacheMu.Unlock()
 	return nil
 }
 

balancer/rls/cache.go

@@ -22,6 +22,8 @@ import (
 	"container/list"
 	"time"
 
+	"github.com/google/uuid"
+	estats "google.golang.org/grpc/experimental/stats"
 	"google.golang.org/grpc/internal/backoff"
 	internalgrpclog "google.golang.org/grpc/internal/grpclog"
 	"google.golang.org/grpc/internal/grpcsync"
@@ -163,22 +165,40 @@ func (l *lru) getLeastRecentlyUsed() cacheKey {
 //
 // It is not safe for concurrent access.
 type dataCache struct {
-	maxSize     int64 // Maximum allowed size.
-	currentSize int64 // Current size.
-	keys        *lru  // Cache keys maintained in lru order.
-	entries     map[cacheKey]*cacheEntry
-	logger      *internalgrpclog.PrefixLogger
-	shutdown    *grpcsync.Event
+	maxSize         int64 // Maximum allowed size.
+	currentSize     int64 // Current size.
+	keys            *lru  // Cache keys maintained in lru order.
+	entries         map[cacheKey]*cacheEntry
+	logger          *internalgrpclog.PrefixLogger
+	shutdown        *grpcsync.Event
+	rlsServerTarget string
+
+	// Read only after initialization.
+	grpcTarget      string
+	uuid            string
+	metricsRecorder estats.MetricsRecorder
 }
 
-func newDataCache(size int64, logger *internalgrpclog.PrefixLogger) *dataCache {
-	return &dataCache{
-		maxSize:  size,
-		keys:     newLRU(),
-		entries:  make(map[cacheKey]*cacheEntry),
-		logger:   logger,
-		shutdown: grpcsync.NewEvent(),
+func newDataCache(size int64, logger *internalgrpclog.PrefixLogger, metricsRecorder estats.MetricsRecorder, grpcTarget string) *dataCache {
+	dc := &dataCache{
+		maxSize:         size,
+		keys:            newLRU(),
+		entries:         make(map[cacheKey]*cacheEntry),
+		logger:          logger,
+		shutdown:        grpcsync.NewEvent(),
+		grpcTarget:      grpcTarget,
+		uuid:            uuid.New().String(),
+		metricsRecorder: metricsRecorder,
 	}
+	cacheSizeMetric.Record(dc.metricsRecorder, 0, grpcTarget, "", dc.uuid)
+	cacheEntriesMetric.Record(dc.metricsRecorder, 0, grpcTarget, "", dc.uuid)
+	return dc
+}
+
+// updateRLSServerTarget updates the RLS Server Target the RLS Balancer is
+// configured with.
+func (dc *dataCache) updateRLSServerTarget(rlsServerTarget string) {
+	dc.rlsServerTarget = rlsServerTarget
 }
 
 // resize changes the maximum allowed size of the data cache.
@@ -319,6 +339,7 @@ func (dc *dataCache) updateEntrySize(entry *cacheEntry, newSize int64) {
 	dc.currentSize -= entry.size
 	entry.size = newSize
 	dc.currentSize += entry.size
+	cacheSizeMetric.Record(dc.metricsRecorder, dc.currentSize, dc.grpcTarget, dc.rlsServerTarget, dc.uuid)
 }
 
 func (dc *dataCache) getEntry(key cacheKey) *cacheEntry {
@@ -351,6 +372,8 @@ func (dc *dataCache) deleteAndCleanup(key cacheKey, entry *cacheEntry) {
 	delete(dc.entries, key)
 	dc.currentSize -= entry.size
 	dc.keys.removeEntry(key)
+	cacheSizeMetric.Record(dc.metricsRecorder, dc.currentSize, dc.grpcTarget, dc.rlsServerTarget, dc.uuid)
+	cacheEntriesMetric.Record(dc.metricsRecorder, int64(len(dc.entries)), dc.grpcTarget, dc.rlsServerTarget, dc.uuid)
 }
 
 func (dc *dataCache) stop() {

balancer/rls/cache_test.go

@@ -25,6 +25,7 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-cmp/cmp/cmpopts"
 	"google.golang.org/grpc/internal/backoff"
+	"google.golang.org/grpc/internal/testutils/stats"
 )
 
 var (
@@ -119,7 +120,7 @@ func (s) TestLRU_BasicOperations(t *testing.T) {
 
 func (s) TestDataCache_BasicOperations(t *testing.T) {
 	initCacheEntries()
-	dc := newDataCache(5, nil)
+	dc := newDataCache(5, nil, &stats.NoopMetricsRecorder{}, "")
 	for i, k := range cacheKeys {
 		dc.addEntry(k, cacheEntries[i])
 	}
@@ -133,7 +134,7 @@ func (s) TestDataCache_BasicOperations(t *testing.T) {
 
 func (s) TestDataCache_AddForcesResize(t *testing.T) {
 	initCacheEntries()
-	dc := newDataCache(1, nil)
+	dc := newDataCache(1, nil, &stats.NoopMetricsRecorder{}, "")
 
 	// The first entry in cacheEntries has a minimum expiry time in the future.
 	// This entry would stop the resize operation since we do not evict entries
@@ -162,7 +163,7 @@ func (s) TestDataCache_AddForcesResize(t *testing.T) {
 
 func (s) TestDataCache_Resize(t *testing.T) {
 	initCacheEntries()
-	dc := newDataCache(5, nil)
+	dc := newDataCache(5, nil, &stats.NoopMetricsRecorder{}, "")
 	for i, k := range cacheKeys {
 		dc.addEntry(k, cacheEntries[i])
 	}
@@ -193,7 +194,7 @@ func (s) TestDataCache_Resize(t *testing.T) {
 
 func (s) TestDataCache_EvictExpiredEntries(t *testing.T) {
 	initCacheEntries()
-	dc := newDataCache(5, nil)
+	dc := newDataCache(5, nil, &stats.NoopMetricsRecorder{}, "")
 	for i, k := range cacheKeys {
 		dc.addEntry(k, cacheEntries[i])
 	}
@@ -220,7 +221,7 @@ func (s) TestDataCache_ResetBackoffState(t *testing.T) {
 	}
 
 	initCacheEntries()
-	dc := newDataCache(5, nil)
+	dc := newDataCache(5, nil, &stats.NoopMetricsRecorder{}, "")
 	for i, k := range cacheKeys {
 		dc.addEntry(k, cacheEntries[i])
 	}

internal/testutils/stats/test_metrics_recorder.go

@@ -242,3 +242,17 @@ func (r *TestMetricsRecorder) TagConn(ctx context.Context, _ *stats.ConnTagInfo)
 }
 
 func (r *TestMetricsRecorder) HandleConn(context.Context, stats.ConnStats) {}
+
+// NoopMetricsRecorder is a noop MetricsRecorder to be used in tests to prevent
+// nil panics.
+type NoopMetricsRecorder struct{}
+
+func (r *NoopMetricsRecorder) RecordInt64Count(*estats.Int64CountHandle, int64, ...string) {}
+
+func (r *NoopMetricsRecorder) RecordFloat64Count(*estats.Float64CountHandle, float64, ...string) {}
+
+func (r *NoopMetricsRecorder) RecordInt64Histo(*estats.Int64HistoHandle, int64, ...string) {}
+
+func (r *NoopMetricsRecorder) RecordFloat64Histo(*estats.Float64HistoHandle, float64, ...string) {}
+
+func (r *NoopMetricsRecorder) RecordInt64Gauge(*estats.Int64GaugeHandle, int64, ...string) {}