chore(spanner): generate client_hash metric attribute using FNV (#10983)

Author: rahul2393

spanner/metrics.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"hash/fnv"
 	"strings"
 
 	"log"
@@ -125,6 +126,47 @@ var (
 		return uuid.NewString() + "@" + strconv.FormatInt(int64(os.Getpid()), 10) + "@" + hostname, nil
 	}
 
+	// generateClientHash generates a 6-digit zero-padded lowercase hexadecimal hash
+	// using the 10 most significant bits of a 64-bit hash value.
+	//
+	// The primary purpose of this function is to generate a hash value for the `client_hash`
+	// resource label using `client_uid` metric field. The range of values is chosen to be small
+	// enough to keep the cardinality of the Resource targets under control. Note: If at later time
+	// the range needs to be increased, it can be done by increasing the value of `kPrefixLength` to
+	// up to 24 bits without changing the format of the returned value.
+	generateClientHash = func(clientUID string) string {
+		if clientUID == "" {
+			return "000000"
+		}
+
+		// Use FNV hash function to generate a 64-bit hash
+		hasher := fnv.New64()
+		hasher.Write([]byte(clientUID))
+		hashValue := hasher.Sum64()
+
+		// Extract the 10 most significant bits
+		// Shift right by 54 bits to get the 10 most significant bits
+		kPrefixLength := 10
+		tenMostSignificantBits := hashValue >> (64 - kPrefixLength)
+
+		// Format the result as a 6-digit zero-padded hexadecimal string
+		return fmt.Sprintf("%06x", tenMostSignificantBits)
+	}
+
+	detectClientLocation = func(ctx context.Context) string {
+		resource, err := gcp.NewDetector().Detect(ctx)
+		if err != nil {
+			return "global"
+		}
+		for _, attr := range resource.Attributes() {
+			if attr.Key == semconv.CloudRegionKey {
+				return attr.Value.AsString()
+			}
+		}
+		// If region is not found, return global
+		return "global"
+	}
+
 	exporterOpts = []option.ClientOption{}
 )
 
@@ -151,20 +193,6 @@ type builtinMetricsTracerFactory struct {
 	attemptCount       metric.Int64Counter     // Counter for the number of attempts.
 }
 
-func detectClientLocation(ctx context.Context) string {
-	resource, err := gcp.NewDetector().Detect(ctx)
-	if err != nil {
-		return "global"
-	}
-	for _, attr := range resource.Attributes() {
-		if attr.Key == semconv.CloudRegionKey {
-			return attr.Value.AsString()
-		}
-	}
-	// If region is not found, return global
-	return "global"
-}
-
 func newBuiltinMetricsTracerFactory(ctx context.Context, dbpath string, metricsProvider metric.MeterProvider) (*builtinMetricsTracerFactory, error) {
 	clientUID, err := generateClientUID()
 	if err != nil {
@@ -183,7 +211,7 @@ func newBuiltinMetricsTracerFactory(ctx context.Context, dbpath string, metricsP
 			attribute.String(metricLabelKeyDatabase, database),
 			attribute.String(metricLabelKeyClientUID, clientUID),
 			attribute.String(metricLabelKeyClientName, clientName),
-			attribute.String(monitoredResLabelKeyClientHash, "cloud_spanner_client_raw_metrics"),
+			attribute.String(monitoredResLabelKeyClientHash, generateClientHash(clientUID)),
 			// Skipping instance config until we have a way to get it
 			attribute.String(monitoredResLabelKeyInstanceConfig, "unknown"),
 			attribute.String(monitoredResLabelKeyLocation, detectClientLocation(ctx)),

spanner/metrics_test.go

@@ -18,6 +18,7 @@ package spanner
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"sort"
 	"testing"
@@ -41,21 +42,19 @@ func TestNewBuiltinMetricsTracerFactory(t *testing.T) {
 	os.Setenv("SPANNER_ENABLE_BUILTIN_METRICS", "true")
 	defer os.Unsetenv("SPANNER_ENABLE_BUILTIN_METRICS")
 	ctx := context.Background()
-	project := "test-project"
-	instance := "test-instance"
 	clientUID := "test-uid"
 	createSessionRPC := "Spanner.BatchCreateSessions"
 	if isMultiplexEnabled {
 		createSessionRPC = "Spanner.CreateSession"
 	}
 
 	wantClientAttributes := []attribute.KeyValue{
-		attribute.String(monitoredResLabelKeyProject, project),
-		attribute.String(monitoredResLabelKeyInstance, instance),
+		attribute.String(monitoredResLabelKeyProject, "[PROJECT]"),
+		attribute.String(monitoredResLabelKeyInstance, "[INSTANCE]"),
 		attribute.String(metricLabelKeyDatabase, "[DATABASE]"),
 		attribute.String(metricLabelKeyClientUID, clientUID),
 		attribute.String(metricLabelKeyClientName, clientName),
-		attribute.String(monitoredResLabelKeyClientHash, "cloud_spanner_client_raw_metrics"),
+		attribute.String(monitoredResLabelKeyClientHash, "0000ed"),
 		attribute.String(monitoredResLabelKeyInstanceConfig, "unknown"),
 		attribute.String(monitoredResLabelKeyLocation, "global"),
 	}
@@ -74,11 +73,16 @@ func TestNewBuiltinMetricsTracerFactory(t *testing.T) {
 
 	// return constant client UID instead of random, so that attributes can be compared
 	origGenerateClientUID := generateClientUID
+	origDetectClientLocation := detectClientLocation
 	generateClientUID = func() (string, error) {
 		return clientUID, nil
 	}
+	detectClientLocation = func(ctx context.Context) string {
+		return "global"
+	}
 	defer func() {
 		generateClientUID = origGenerateClientUID
+		detectClientLocation = origDetectClientLocation
 	}()
 
 	// Setup mock monitoring server
@@ -153,8 +157,7 @@ func TestNewBuiltinMetricsTracerFactory(t *testing.T) {
 				t.Errorf("builtinEnabled: got: %v, want: %v", client.metricsTracerFactory.enabled, test.wantBuiltinEnabled)
 			}
 
-			if diff := testutil.Diff(client.metricsTracerFactory.clientAttributes, wantClientAttributes,
-				cmpopts.IgnoreUnexported(attribute.KeyValue{}, attribute.Value{})); diff != "" {
+			if diff := testutil.Diff(client.metricsTracerFactory.clientAttributes, wantClientAttributes, cmpopts.EquateComparable(attribute.KeyValue{}, attribute.Value{})); diff != "" {
 				t.Errorf("clientAttributes: got=-, want=+ \n%v", diff)
 			}
 
@@ -235,3 +238,49 @@ func TestNewBuiltinMetricsTracerFactory(t *testing.T) {
 		})
 	}
 }
+
+// TestGenerateClientHash tests the generateClientHash function.
+func TestGenerateClientHash(t *testing.T) {
+	tests := []struct {
+		name             string
+		clientUID        string
+		expectedValue    string
+		expectedLength   int
+		expectedMaxValue int64
+	}{
+		{"Simple UID", "exampleUID", "00006b", 6, 0x3FF},
+		{"Empty UID", "", "000000", 6, 0x3FF},
+		{"Special Characters", "!@#$%^&*()", "000389", 6, 0x3FF},
+		{"Very Long UID", "aVeryLongUniqueIdentifierThatExceedsNormalLength", "000125", 6, 0x3FF},
+		{"Numeric UID", "1234567890", "00003e", 6, 0x3FF},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			hash := generateClientHash(tt.clientUID)
+			if hash != tt.expectedValue {
+				t.Errorf("expected hash value %s, got %s", tt.expectedValue, hash)
+			}
+			// Check if the hash length is 6
+			if len(hash) != tt.expectedLength {
+				t.Errorf("expected hash length %d, got %d", tt.expectedLength, len(hash))
+			}
+
+			// Check if the hash is in the range [000000, 0003ff]
+			hashValue, err := parseHex(hash)
+			if err != nil {
+				t.Errorf("failed to parse hash: %v", err)
+			}
+			if hashValue < 0 || hashValue > tt.expectedMaxValue {
+				t.Errorf("expected hash value in range [0, %d], got %d", tt.expectedMaxValue, hashValue)
+			}
+		})
+	}
+}
+
+// parseHex converts a hexadecimal string to an int64.
+func parseHex(hexStr string) (int64, error) {
+	var value int64
+	_, err := fmt.Sscanf(hexStr, "%x", &value)
+	return value, err
+}