[Tiered Cache] Use ConcurrentHashMap explicitly in IndicesRequestCache

server/src/internalClusterTest/java/org/opensearch/indices/IndicesRequestCacheIT.java

@@ -1168,7 +1168,7 @@ public void testCacheCleanupAfterIndexDeletion() throws Exception {
         }, cacheCleanIntervalInMillis * 2, TimeUnit.MILLISECONDS);
     }
 
-    // when staleness threshold is lower than staleness, it should clean the cache from all indices having stale keys
+    // when staleness threshold is lower than staleness, it should clean cache from all indices having stale keys
     public void testStaleKeysCleanupWithMultipleIndices() throws Exception {
         int cacheCleanIntervalInMillis = 10;
         String node = internalCluster().startNode(

server/src/main/java/org/opensearch/indices/IndicesRequestCache.java

@@ -81,6 +81,7 @@
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -506,15 +507,15 @@ public int hashCode() {
      * */
     class IndicesRequestCacheCleanupManager implements Closeable {
         private final Set<CleanupKey> keysToClean;
-        private final ConcurrentMap<ShardId, ConcurrentMap<String, Integer>> cleanupKeyToCountMap;
+        private final ConcurrentHashMap<ShardId, ConcurrentHashMap<String, Integer>> cleanupKeyToCountMap;
         private final AtomicInteger staleKeysCount;
         private volatile double stalenessThreshold;
         private final IndicesRequestCacheCleaner cacheCleaner;
 
         IndicesRequestCacheCleanupManager(ThreadPool threadpool, TimeValue cleanInterval, double stalenessThreshold) {
             this.stalenessThreshold = stalenessThreshold;
             this.keysToClean = ConcurrentCollections.newConcurrentSet();
-            this.cleanupKeyToCountMap = ConcurrentCollections.newConcurrentMap();
+            this.cleanupKeyToCountMap = new ConcurrentHashMap<>();
             this.staleKeysCount = new AtomicInteger(0);
             this.cacheCleaner = new IndicesRequestCacheCleaner(this, threadpool, cleanInterval);
             threadpool.schedule(cacheCleaner, cleanInterval, ThreadPool.Names.SAME);
@@ -572,8 +573,7 @@ private void updateStaleCountOnCacheInsert(CleanupKey cleanupKey) {
 
         // pkg-private for testing
         void addToCleanupKeyToCountMap(ShardId shardId, String readerCacheKeyId) {
-            cleanupKeyToCountMap.computeIfAbsent(shardId, k -> ConcurrentCollections.newConcurrentMap())
-                .merge(readerCacheKeyId, 1, Integer::sum);
+            cleanupKeyToCountMap.computeIfAbsent(shardId, k -> new ConcurrentHashMap<>()).merge(readerCacheKeyId, 1, Integer::sum);
         }
 
         /**
@@ -831,7 +831,7 @@ public void close() {
         }
 
         // for testing
-        ConcurrentMap<ShardId, ConcurrentMap<String, Integer>> getCleanupKeyToCountMap() {
+        ConcurrentHashMap<ShardId, ConcurrentHashMap<String, Integer>> getCleanupKeyToCountMap() {
             return cleanupKeyToCountMap;
         }
 

server/src/test/java/org/opensearch/indices/IndicesRequestCacheTests.java

@@ -101,7 +101,6 @@
 import java.util.Optional;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -491,7 +490,8 @@ public void testStaleCount_OnRemovalNotificationOfStaleKey_DecrementsStaleCount(
             indexShard.hashCode()
         );
         // test the mapping
-        ConcurrentMap<ShardId, ConcurrentMap<String, Integer>> cleanupKeyToCountMap = cache.cacheCleanupManager.getCleanupKeyToCountMap();
+        ConcurrentHashMap<ShardId, ConcurrentHashMap<String, Integer>> cleanupKeyToCountMap = cache.cacheCleanupManager
+            .getCleanupKeyToCountMap();
         // shard id should exist
         assertTrue(cleanupKeyToCountMap.containsKey(shardId));
         // reader CacheKeyId should NOT exist
@@ -554,7 +554,8 @@ public void testStaleCount_OnRemovalNotificationOfNonStaleKey_DoesNotDecrementsS
         );
 
         // test the mapping
-        ConcurrentMap<ShardId, ConcurrentMap<String, Integer>> cleanupKeyToCountMap = cache.cacheCleanupManager.getCleanupKeyToCountMap();
+        ConcurrentHashMap<ShardId, ConcurrentHashMap<String, Integer>> cleanupKeyToCountMap = cache.cacheCleanupManager
+            .getCleanupKeyToCountMap();
         // shard id should exist
         assertTrue(cleanupKeyToCountMap.containsKey(shardId));
         // reader CacheKeyId should NOT exist
@@ -722,7 +723,8 @@ public void testCleanupKeyToCountMapAreSetAppropriately() throws Exception {
         cache.getOrCompute(getEntity(indexShard), getLoader(reader), reader, getTermBytes());
         assertEquals(1, cache.count());
         // test the mappings
-        ConcurrentMap<ShardId, ConcurrentMap<String, Integer>> cleanupKeyToCountMap = cache.cacheCleanupManager.getCleanupKeyToCountMap();
+        ConcurrentHashMap<ShardId, ConcurrentHashMap<String, Integer>> cleanupKeyToCountMap = cache.cacheCleanupManager
+            .getCleanupKeyToCountMap();
         assertEquals(1, (int) cleanupKeyToCountMap.get(shardId).get(getReaderCacheKeyId(reader)));
 
         cache.getOrCompute(getEntity(indexShard), getLoader(secondReader), secondReader, getTermBytes());
@@ -796,15 +798,15 @@ public void testCleanupKeyToCountMapAreSetAppropriately() throws Exception {
     }
 
     // test adding to cleanupKeyToCountMap with multiple threads
-    public void testAddToCleanupKeyToCountMap() throws Exception {
+    public void testAddingToCleanupKeyToCountMapWorksAppropriatelyWithMultipleThreads() throws Exception {
         threadPool = getThreadPool();
         Settings settings = Settings.builder().put(INDICES_REQUEST_CACHE_STALENESS_THRESHOLD_SETTING.getKey(), "51%").build();
         cache = getIndicesRequestCache(settings);
 
         int numberOfThreads = 10;
         int numberOfIterations = 1000;
         Phaser phaser = new Phaser(numberOfThreads + 1); // +1 for the main thread
-        AtomicBoolean exceptionDetected = new AtomicBoolean(false);
+        AtomicBoolean concurrentModificationExceptionDetected = new AtomicBoolean(false);
 
         ExecutorService executorService = Executors.newFixedThreadPool(numberOfThreads);
 
@@ -817,7 +819,7 @@ public void testAddToCleanupKeyToCountMap() throws Exception {
                     }
                 } catch (ConcurrentModificationException e) {
                     logger.error("ConcurrentModificationException detected in thread : " + e.getMessage());
-                    exceptionDetected.set(true); // Set flag if exception is detected
+                    concurrentModificationExceptionDetected.set(true); // Set flag if exception is detected
                 }
             });
         }
@@ -836,13 +838,17 @@ public void testAddToCleanupKeyToCountMap() throws Exception {
                 }
             } catch (ConcurrentModificationException e) {
                 logger.error("ConcurrentModificationException detected in main thread : " + e.getMessage());
-                exceptionDetected.set(true); // Set flag if exception is detected
+                concurrentModificationExceptionDetected.set(true); // Set flag if exception is detected
             }
         });
 
         executorService.shutdown();
-        executorService.awaitTermination(60, TimeUnit.SECONDS);
-        assertFalse(exceptionDetected.get());
+        assertTrue(executorService.awaitTermination(60, TimeUnit.SECONDS));
+        assertEquals(
+            numberOfThreads * numberOfIterations,
+            cache.cacheCleanupManager.getCleanupKeyToCountMap().get(indexShard.shardId()).size()
+        );
+        assertFalse(concurrentModificationExceptionDetected.get());
     }
 
     private IndicesRequestCache getIndicesRequestCache(Settings settings) {