[Backport 2.x] [Tiered Caching] Bug fix for IndicesRequestCache StaleKey management

CHANGELOG.md

@@ -65,6 +65,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Enabled mockTelemetryPlugin for IT and fixed OOM issues ([#13054](https://github.com/opensearch-project/OpenSearch/pull/13054))
 - Fix from and size parameter can be negative when searching ([#13047](https://github.com/opensearch-project/OpenSearch/pull/13047))
 - Fix implement mark() and markSupported() in class FilterStreamInput ([#13098](https://github.com/opensearch-project/OpenSearch/pull/13098))
+- Fix IndicesRequestCache Stale calculation ([#13070](https://github.com/opensearch-project/OpenSearch/pull/13070)]
 - Fix snapshot _status API to return correct status for partial snapshots ([#12812](https://github.com/opensearch-project/OpenSearch/pull/12812))
 - Improve the error messages for _stats with closed indices ([#13012](https://github.com/opensearch-project/OpenSearch/pull/13012))
 - Ignore BaseRestHandler unconsumed content check as it's always consumed. ([#13290](https://github.com/opensearch-project/OpenSearch/pull/13290))

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

@@ -47,6 +47,7 @@
 import org.opensearch.common.cache.LoadAwareCacheLoader;
 import org.opensearch.common.cache.RemovalListener;
 import org.opensearch.common.cache.RemovalNotification;
+import org.opensearch.common.cache.RemovalReason;
 import org.opensearch.common.cache.policy.CachedQueryResult;
 import org.opensearch.common.cache.serializer.BytesReferenceSerializer;
 import org.opensearch.common.cache.service.CacheService;
@@ -216,19 +217,16 @@ void clear(CacheEntity entity) {
     public void onRemoval(RemovalNotification<ICacheKey<Key>, BytesReference> notification) {
         // In case this event happens for an old shard, we can safely ignore this as we don't keep track for old
         // shards as part of request cache.
-
         // Pass a new removal notification containing Key rather than ICacheKey<Key> to the CacheEntity for backwards compatibility.
         Key key = notification.getKey().key;
         RemovalNotification<Key, BytesReference> newNotification = new RemovalNotification<>(
             key,
             notification.getValue(),
             notification.getRemovalReason()
         );
-
         cacheEntityLookup.apply(key.shardId).ifPresent(entity -> entity.onRemoval(newNotification));
-        cacheCleanupManager.updateCleanupKeyToCountMapOnCacheEviction(
-            new CleanupKey(cacheEntityLookup.apply(key.shardId).orElse(null), key.readerCacheKeyId)
-        );
+        CleanupKey cleanupKey = new CleanupKey(cacheEntityLookup.apply(key.shardId).orElse(null), key.readerCacheKeyId);
+        cacheCleanupManager.updateStaleCountOnEntryRemoval(cleanupKey, newNotification);
     }
 
     private ICacheKey<Key> getICacheKey(Key key) {
@@ -272,10 +270,11 @@ BytesReference getOrCompute(
                     OpenSearchDirectoryReader.addReaderCloseListener(reader, cleanupKey);
                 }
             }
-            cacheCleanupManager.updateCleanupKeyToCountMapOnCacheInsertion(cleanupKey);
+            cacheCleanupManager.updateStaleCountOnCacheInsert(cleanupKey);
         } else {
             cacheEntity.onHit();
         }
+
         return value;
     }
 
@@ -508,7 +507,7 @@ void enqueueCleanupKey(CleanupKey cleanupKey) {
          *
          * @param cleanupKey the CleanupKey to be updated in the map
          */
-        private void updateCleanupKeyToCountMapOnCacheInsertion(CleanupKey cleanupKey) {
+        private void updateStaleCountOnCacheInsert(CleanupKey cleanupKey) {
             if (stalenessThreshold == 0.0 || cleanupKey.entity == null) {
                 return;
             }
@@ -524,8 +523,29 @@ private void updateCleanupKeyToCountMapOnCacheInsertion(CleanupKey cleanupKey) {
             cleanupKeyToCountMap.computeIfAbsent(shardId, k -> new HashMap<>()).merge(cleanupKey.readerCacheKeyId, 1, Integer::sum);
         }
 
-        private void updateCleanupKeyToCountMapOnCacheEviction(CleanupKey cleanupKey) {
-            if (stalenessThreshold == 0.0 || cleanupKey.entity == null) {
+        /**
+         * Handles the eviction of a cache entry.
+         *
+         * <p>This method is called when an entry is evicted from the cache.
+         * We consider all removal notifications except with the reason Replaced
+         * {@link #incrementStaleKeysCount} would have removed the entries from the map and increment the {@link #staleKeysCount}
+         * Hence we decrement {@link #staleKeysCount} if we do not find the shardId or readerCacheKeyId in the map.
+         * Skip decrementing staleKeysCount if we find the shardId or readerCacheKeyId in the map since it would have not been accounted for in the staleKeysCount in
+         *
+         * @param cleanupKey   the CleanupKey that has been evicted from the cache
+         * @param notification RemovalNotification of the cache entry evicted
+         */
+        private void updateStaleCountOnEntryRemoval(CleanupKey cleanupKey, RemovalNotification<Key, BytesReference> notification) {
+            if (notification.getRemovalReason() == RemovalReason.REPLACED) {
+                // The reason of the notification is REPLACED when a cache entry's value is updated, since replacing an entry
+                // does not affect the staleness count, we skip such notifications.
+                return;
+            }
+            if (cleanupKey.entity == null) {
+                // entity will only be null when the shard is closed/deleted
+                // we would have accounted this in staleKeysCount when the closing/deletion of shard would have closed the associated
+                // readers
+                staleKeysCount.decrementAndGet();
                 return;
             }
             IndexShard indexShard = (IndexShard) cleanupKey.entity.getCacheIdentity();
@@ -535,23 +555,41 @@ private void updateCleanupKeyToCountMapOnCacheEviction(CleanupKey cleanupKey) {
             }
             ShardId shardId = indexShard.shardId();
 
-            cleanupKeyToCountMap.computeIfPresent(shardId, (shard, keyCountMap) -> {
-                keyCountMap.computeIfPresent(cleanupKey.readerCacheKeyId, (key, currentValue) -> {
-                    // decrement the stale key count
+            cleanupKeyToCountMap.compute(shardId, (key, readerCacheKeyMap) -> {
+                if (readerCacheKeyMap == null || !readerCacheKeyMap.containsKey(cleanupKey.readerCacheKeyId)) {
+                    // If ShardId is not present or readerCacheKeyId is not present
+                    // it should have already been accounted for and hence been removed from this map
+                    // so decrement staleKeysCount
                     staleKeysCount.decrementAndGet();
-                    int newValue = currentValue - 1;
-                    // Remove the key if the new value is zero by returning null; otherwise, update with the new value.
-                    return newValue == 0 ? null : newValue;
-                });
-                return keyCountMap;
+                    // Return the current map
+                    return readerCacheKeyMap;
+                } else {
+                    // If it is in the map, it is not stale yet.
+                    // Proceed to adjust the count for the readerCacheKeyId in the map
+                    // but do not decrement the staleKeysCount
+                    Integer count = readerCacheKeyMap.get(cleanupKey.readerCacheKeyId);
+                    // this should never be null
+                    assert (count != null && count >= 0);
+                    // Reduce the count by 1
+                    int newCount = count - 1;
+                    if (newCount > 0) {
+                        // Update the map with the new count
+                        readerCacheKeyMap.put(cleanupKey.readerCacheKeyId, newCount);
+                    } else {
+                        // Remove the readerCacheKeyId entry if new count is zero
+                        readerCacheKeyMap.remove(cleanupKey.readerCacheKeyId);
+                    }
+                    // If after modification, the readerCacheKeyMap is empty, we return null to remove the ShardId entry
+                    return readerCacheKeyMap.isEmpty() ? null : readerCacheKeyMap;
+                }
             });
         }
 
         /**
          * Updates the count of stale keys in the cache.
          * This method is called when a CleanupKey is added to the keysToClean set.
          *
-         * It increments the staleKeysCount by the count of the CleanupKey in the cleanupKeyToCountMap.
+         * <p>It increments the staleKeysCount by the count of the CleanupKey in the cleanupKeyToCountMap.
          * If the CleanupKey's readerCacheKeyId is null or the CleanupKey's entity is not open, it increments the staleKeysCount
          * by the total count of keys associated with the CleanupKey's ShardId in the cleanupKeyToCountMap and removes the ShardId from the map.
          *
@@ -569,7 +607,7 @@ private void incrementStaleKeysCount(CleanupKey cleanupKey) {
             ShardId shardId = indexShard.shardId();
 
             // Using computeIfPresent to atomically operate on the countMap for a given shardId
-            cleanupKeyToCountMap.computeIfPresent(shardId, (key, countMap) -> {
+            cleanupKeyToCountMap.computeIfPresent(shardId, (currentShardId, countMap) -> {
                 if (cleanupKey.readerCacheKeyId == null) {
                     // Aggregate and add to staleKeysCount atomically if readerCacheKeyId is null
                     int totalSum = countMap.values().stream().mapToInt(Integer::intValue).sum();
@@ -578,18 +616,19 @@ private void incrementStaleKeysCount(CleanupKey cleanupKey) {
                     return null;
                 } else {
                     // Update staleKeysCount based on specific readerCacheKeyId, then remove it from the countMap
-                    countMap.computeIfPresent(cleanupKey.readerCacheKeyId, (k, v) -> {
-                        staleKeysCount.addAndGet(v);
+                    countMap.computeIfPresent(cleanupKey.readerCacheKeyId, (readerCacheKey, count) -> {
+                        staleKeysCount.addAndGet(count);
                         // Return null to remove the key after updating staleKeysCount
                         return null;
                     });
-
                     // Check if countMap is empty after removal to decide if we need to remove the shardId entry
                     if (countMap.isEmpty()) {
-                        return null; // Returning null removes the entry for shardId
+                        // Returning null removes the entry for shardId
+                        return null;
                     }
                 }
-                return countMap; // Return the modified countMap to keep the mapping
+                // Return the modified countMap to retain updates
+                return countMap;
             });
         }
 
@@ -715,6 +754,11 @@ public void close() {
             this.cacheCleaner.close();
         }
 
+        // for testing
+        ConcurrentMap<ShardId, HashMap<String, Integer>> getCleanupKeyToCountMap() {
+            return cleanupKeyToCountMap;
+        }
+
         private final class IndicesRequestCacheCleaner implements Runnable, Releasable {
 
             private final IndicesRequestCacheCleanupManager cacheCleanupManager;