Added RBM keystore impl

Signed-off-by: Peter Alfonsi <[email protected]>

plugins/cache-ehcache/src/main/java/org/opensearch/cache/keystore/KeyStoreStats.java

@@ -0,0 +1,44 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.cache.keystore;
+
+import org.opensearch.common.metrics.CounterMetric;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * A stats holder for use in KeyLookupStore implementations.
+ * Getters should be exposed by the KeyLookupStore which uses it.
+ */
+public class KeyStoreStats {
+    // Number of entries
+    protected CounterMetric size;
+    // Memory cap in bytes
+    protected long memSizeCapInBytes;
+    // Number of add attempts
+    protected CounterMetric numAddAttempts;
+    // Number of collisions
+    protected CounterMetric numCollisions;
+    // True if the store is at capacity
+    protected AtomicBoolean atCapacity;
+    // Number of removal attempts
+    protected CounterMetric numRemovalAttempts;
+    // Number of successful removal attempts
+    protected CounterMetric numSuccessfulRemovals;
+
+    protected KeyStoreStats(long memSizeCapInBytes) {
+        this.size = new CounterMetric();
+        this.numAddAttempts = new CounterMetric();
+        this.numCollisions = new CounterMetric();
+        this.memSizeCapInBytes = memSizeCapInBytes;
+        this.atCapacity = new AtomicBoolean(false);
+        this.numRemovalAttempts = new CounterMetric();
+        this.numSuccessfulRemovals = new CounterMetric();
+    }
+}