fix: add client id to metrics to avoid collisions

google-cloud-spanner/src/main/java/com/google/cloud/spanner/MetricRegistryConstants.java

@@ -23,6 +23,8 @@
 class MetricRegistryConstants {
 
   // The label keys are used to uniquely identify timeseries.
+  private static final LabelKey CLIENT_ID =
+      LabelKey.create("client_id", "User defined database client id");
   private static final LabelKey DATABASE = LabelKey.create("database", "Target database");
   private static final LabelKey INSTANCE_ID =
       LabelKey.create("instance_id", "Name of the instance");
@@ -33,10 +35,10 @@ class MetricRegistryConstants {
   private static final LabelValue UNSET_LABEL = LabelValue.create(null);
 
   static final ImmutableList<LabelKey> SPANNER_LABEL_KEYS =
-      ImmutableList.of(DATABASE, INSTANCE_ID, LIBRARY_VERSION);
+      ImmutableList.of(CLIENT_ID, DATABASE, INSTANCE_ID, LIBRARY_VERSION);
 
   static final ImmutableList<LabelValue> SPANNER_DEFAULT_LABEL_VALUES =
-      ImmutableList.of(UNSET_LABEL, UNSET_LABEL, UNSET_LABEL);
+      ImmutableList.of(UNSET_LABEL, UNSET_LABEL, UNSET_LABEL, UNSET_LABEL);
 
   /** Unit to represent counts. */
   static final String COUNT = "1";

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerImpl.java

@@ -62,6 +62,24 @@ class SpannerImpl extends BaseService<SpannerOptions> implements Spanner {
   static final String QUERY = "CloudSpannerOperation.ExecuteStreamingQuery";
   static final String READ = "CloudSpannerOperation.ExecuteStreamingRead";
 
+  private static final Object CLIENT_ID_LOCK = new Object();
+
+  @GuardedBy("CLIENT_ID_LOCK")
+  private static final Map<DatabaseId, Long> CLIENT_IDS = new HashMap<>();
+
+  private static String nextDatabaseClientId(DatabaseId databaseId) {
+    synchronized (CLIENT_ID_LOCK) {
+      Long id = CLIENT_IDS.get(databaseId);
+      if (id == null) {
+        id = 1L;
+      } else {
+        id++;
+      }
+      CLIENT_IDS.put(databaseId, id);
+      return String.format("client-%d", id);
+    }
+  }
+
   private final SpannerRpc gapicRpc;
 
   @GuardedBy("this")
@@ -155,6 +173,7 @@ public DatabaseClient getDatabaseClient(DatabaseId db) {
       } else {
         List<LabelValue> labelValues =
             ImmutableList.of(
+                LabelValue.create(nextDatabaseClientId(db)),
                 LabelValue.create(db.getDatabase()),
                 LabelValue.create(db.getInstanceId().getName()),
                 LabelValue.create(GaxProperties.getLibraryVersion(getOptions().getClass())));

google-cloud-spanner/src/test/java/com/google/cloud/spanner/SessionPoolTest.java

@@ -1579,6 +1579,7 @@ public void testSessionMetrics() throws Exception {
     FakeMetricRegistry metricRegistry = new FakeMetricRegistry();
     List<LabelValue> labelValues =
         Arrays.asList(
+            LabelValue.create("client1"),
             LabelValue.create("database1"),
             LabelValue.create("instance1"),
             LabelValue.create("1.0.0"));