Add metrics for cache instance count

atlasdb-client/src/main/java/com/palantir/atlasdb/AtlasDbMetricNames.java

@@ -106,4 +106,5 @@ private CellFilterMetrics() {
     public static final String LW_CACHE_RATIO_USED = "lockWatchCacheRatioUsed";
     public static final String LW_EVENT_CACHE_FALLBACK_COUNT = "lockWatchEventCacheFallbackCount";
     public static final String LW_VALUE_CACHE_FALLBACK_COUNT = "lockWatchValueCacheFallbackCount";
+    public static final String LW_TRANSACTION_CACHE_INSTANCE_COUNT = "lockWatchTransactionCacheInstanceCount";
 }

atlasdb-impl-shared/src/main/java/com/palantir/atlasdb/keyvalue/api/cache/CacheMetrics.java

@@ -17,6 +17,7 @@
 package com.palantir.atlasdb.keyvalue.api.cache;
 
 import com.codahale.metrics.Counter;
+import com.codahale.metrics.Gauge;
 import com.palantir.atlasdb.AtlasDbMetricNames;
 import com.palantir.atlasdb.util.CurrentValueMetric;
 import com.palantir.atlasdb.util.MetricsManager;
@@ -112,4 +113,9 @@ public void setMaximumCacheSize(long maximumCacheSize) {
                 AtlasDbMetricNames.LW_CACHE_RATIO_USED,
                 () -> () -> cacheSize.getCount() / (double) maximumCacheSize);
     }
+
+    public void setTransactionCacheInstanceCountGauge(Gauge<Integer> getCacheMapCount) {
+        metricsManager.registerOrGetGauge(
+                CacheMetrics.class, AtlasDbMetricNames.LW_TRANSACTION_CACHE_INSTANCE_COUNT, () -> getCacheMapCount);
+    }
 }

atlasdb-impl-shared/src/main/java/com/palantir/atlasdb/keyvalue/api/cache/CacheStoreImpl.java

@@ -51,6 +51,7 @@ final class CacheStoreImpl implements CacheStore {
         this.maxCacheCount = maxCacheCount;
         this.cacheMap = new ConcurrentHashMap<>();
         this.validationProbability = validationProbability;
+        metrics.setTransactionCacheInstanceCountGauge(cacheMap::size);
     }
 
     @Override

atlasdb-impl-shared/src/test/java/com/palantir/atlasdb/keyvalue/api/cache/CacheStoreImplTest.java

@@ -19,14 +19,17 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 
+import com.codahale.metrics.Gauge;
 import com.google.common.collect.ImmutableSet;
 import com.palantir.atlasdb.keyvalue.api.watch.Sequence;
 import com.palantir.atlasdb.keyvalue.api.watch.StartTimestamp;
 import com.palantir.atlasdb.transaction.api.TransactionFailedRetriableException;
 import io.vavr.collection.HashMap;
 import io.vavr.collection.HashSet;
 import org.junit.Test;
+import org.mockito.ArgumentCaptor;
 
 public final class CacheStoreImplTest {
     private static final StartTimestamp TIMESTAMP_1 = StartTimestamp.of(1L);
@@ -49,6 +52,7 @@ public void updatesToSnapshotStoreReflectedInCacheStore() {
                 ValueCacheSnapshotImpl.of(HashMap.empty(), HashSet.empty(), ImmutableSet.of()));
         cacheStore.createCache(TIMESTAMP_2);
         assertThat(cacheStore.getCache(TIMESTAMP_2)).isExactlyInstanceOf(ValidatingTransactionScopedCache.class);
+        assertThat(getTransactionCacheInstanceCount()).isEqualTo(1);
     }
 
     @Test
@@ -66,6 +70,7 @@ public void multipleCallsToGetReturnsTheSameCache() {
         TransactionScopedCache cache2 = cacheStore.getCache(TIMESTAMP_2);
 
         assertThat(cacheStore.getCache(TIMESTAMP_1)).isEqualTo(cache1).isNotEqualTo(cache2);
+        assertThat(getTransactionCacheInstanceCount()).isEqualTo(2);
     }
 
     @Test
@@ -85,6 +90,7 @@ public void cachesExceedingMaximumCountThrows() {
                 .isExactlyInstanceOf(TransactionFailedRetriableException.class)
                 .hasMessage("Exceeded maximum concurrent caches; transaction can be retried, but with caching "
                         + "disabled");
+        assertThat(getTransactionCacheInstanceCount()).isEqualTo(2);
     }
 
     @Test
@@ -99,6 +105,7 @@ public void getCacheDoesNotPersistAnything() {
         assertThat(cacheStore.getCache(TIMESTAMP_1)).isExactlyInstanceOf(NoOpTransactionScopedCache.class);
         cacheStore.createCache(TIMESTAMP_1);
         assertThat(cacheStore.getCache(TIMESTAMP_1)).isExactlyInstanceOf(ValidatingTransactionScopedCache.class);
+        assertThat(getTransactionCacheInstanceCount()).isEqualTo(1);
     }
 
     @Test
@@ -110,5 +117,13 @@ public void noOpCachesAreNotStored() {
         cacheStore.createCache(TIMESTAMP_2);
         assertThat(cacheStore.getCache(TIMESTAMP_1)).isExactlyInstanceOf(NoOpTransactionScopedCache.class);
         assertThat(cacheStore.getCache(TIMESTAMP_2)).isExactlyInstanceOf(NoOpTransactionScopedCache.class);
+        assertThat(getTransactionCacheInstanceCount()).isEqualTo(0);
+    }
+
+    @SuppressWarnings("unchecked")
+    private int getTransactionCacheInstanceCount() {
+        ArgumentCaptor<Gauge<Integer>> cacheInstanceCount = ArgumentCaptor.forClass(Gauge.class);
+        verify(metrics).setTransactionCacheInstanceCountGauge(cacheInstanceCount.capture());
+        return cacheInstanceCount.getValue().getValue();
     }
 }

changelog/@unreleased/pr-5631.v2.yml

@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+  description: Add metric for tracking the count of transaction caches stored in the transaction map, connected to memory leaks such as PDS-185998 and PDS-209612
+  links:
+  - https://github.com/palantir/atlasdb/pull/5631