[Bugfix] Fix TieredSpilloverCache stats not adding correctly when shards are closed

CHANGELOG.md

@@ -82,6 +82,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Fix warnings from SLF4J on startup when repository-s3 is installed ([#16194](https://github.com/opensearch-project/OpenSearch/pull/16194))
 - Fix protobuf-java leak through client library dependencies ([#16254](https://github.com/opensearch-project/OpenSearch/pull/16254))
 - Fix multi-search with template doesn't return status code ([#16265](https://github.com/opensearch-project/OpenSearch/pull/16265))
+- [Tiered Caching] Fix bug in cache stats API ([#16560](https://github.com/opensearch-project/OpenSearch/pull/16560))
 
 ### Security
 

modules/cache-common/src/internalClusterTest/java/org/opensearch/cache/common/tier/TieredSpilloverCacheStatsIT.java

@@ -10,6 +10,7 @@
 
 import org.opensearch.action.admin.cluster.node.stats.NodesStatsRequest;
 import org.opensearch.action.admin.cluster.node.stats.NodesStatsResponse;
+import org.opensearch.action.admin.indices.delete.DeleteIndexRequest;
 import org.opensearch.action.admin.indices.forcemerge.ForceMergeResponse;
 import org.opensearch.action.admin.indices.stats.CommonStatsFlags;
 import org.opensearch.action.search.SearchResponse;
@@ -40,6 +41,7 @@
 import static org.opensearch.cache.common.tier.TieredSpilloverCacheStatsHolder.TIER_DIMENSION_NAME;
 import static org.opensearch.cache.common.tier.TieredSpilloverCacheStatsHolder.TIER_DIMENSION_VALUE_DISK;
 import static org.opensearch.cache.common.tier.TieredSpilloverCacheStatsHolder.TIER_DIMENSION_VALUE_ON_HEAP;
+import static org.opensearch.indices.IndicesService.INDICES_CACHE_CLEAN_INTERVAL_SETTING;
 import static org.opensearch.test.hamcrest.OpenSearchAssertions.assertAcked;
 import static org.opensearch.test.hamcrest.OpenSearchAssertions.assertSearchResponse;
 
@@ -417,6 +419,55 @@ public void testStatsWithMultipleSegments() throws Exception {
         assertTrue(diskCacheStat.getEvictions() == 0);
     }
 
+    public void testClosingShard() throws Exception {
+        // Closing the shard should totally remove the stats associated with that shard.
+        internalCluster().startNodes(
+            1,
+            Settings.builder()
+                .put(defaultSettings(HEAP_CACHE_SIZE_STRING, getNumberOfSegments()))
+                .put(
+                    TieredSpilloverCacheSettings.TOOK_TIME_POLICY_CONCRETE_SETTINGS_MAP.get(CacheType.INDICES_REQUEST_CACHE).getKey(),
+                    new TimeValue(0, TimeUnit.SECONDS)
+                )
+                .put(INDICES_CACHE_CLEAN_INTERVAL_SETTING.getKey(), new TimeValue(1))
+                .build()
+        );
+        String index = "index";
+        Client client = client();
+        startIndex(client, index);
+
+        // First search one time to see how big a single value will be
+        searchIndex(client, index, 0);
+        // get total stats
+        long singleSearchSize = getTotalStats(client).getSizeInBytes();
+        // Select numbers so we get some values on both heap and disk
+        int itemsOnHeap = HEAP_CACHE_SIZE / (int) singleSearchSize;
+        int itemsOnDisk = 1 + randomInt(30); // The first one we search (to get the size) always goes to disk
+        int expectedEntries = itemsOnHeap + itemsOnDisk;
+
+        for (int i = 1; i < expectedEntries; i++) {
+            // Cause misses
+            searchIndex(client, index, i);
+        }
+        int expectedMisses = itemsOnHeap + itemsOnDisk;
+
+        // Cause some hits
+        int expectedHits = randomIntBetween(itemsOnHeap, expectedEntries); // Select it so some hits come from both tiers
+        for (int i = 0; i < expectedHits; i++) {
+            searchIndex(client, index, i);
+        }
+
+        // Check the new stats API values are as expected
+        assertEquals(
+            new ImmutableCacheStats(expectedHits, expectedMisses, 0, expectedEntries * singleSearchSize, expectedEntries),
+            getTotalStats(client)
+        );
+
+        // Closing the index should close the shard
+        assertAcked(client().admin().indices().delete(new DeleteIndexRequest("index")).get());
+        assertEquals(new ImmutableCacheStats(0, 0, 0, 0, 0), getTotalStats(client));
+    }
+
     private void startIndex(Client client, String indexName) throws InterruptedException {
         assertAcked(
             client.admin()

modules/cache-common/src/main/java/org/opensearch/cache/common/tier/TieredSpilloverCache.java

@@ -373,14 +373,14 @@ private V compute(ICacheKey<K> key, LoadAwareCacheLoader<ICacheKey<K>, V> loader
 
         @Override
         public void invalidate(ICacheKey<K> key) {
-            for (Map.Entry<ICache<K, V>, TierInfo> cacheEntry : caches.entrySet()) {
-                if (key.getDropStatsForDimensions()) {
-                    List<String> dimensionValues = statsHolder.getDimensionsWithTierValue(key.dimensions, cacheEntry.getValue().tierName);
-                    statsHolder.removeDimensions(dimensionValues);
-                }
-                if (key.key != null) {
-                    try (ReleasableLock ignore = writeLock.acquire()) {
-                        cacheEntry.getKey().invalidate(key);
+            if (key.getDropStatsForDimensions()) {
+                statsHolder.removeDimensions(key.dimensions);
+            } else {
+                for (Map.Entry<ICache<K, V>, TierInfo> cacheEntry : caches.entrySet()) {
+                    if (key.key != null) {
+                        try (ReleasableLock ignore = writeLock.acquire()) {
+                            cacheEntry.getKey().invalidate(key);
+                        }
                     }
                 }
             }

modules/cache-common/src/main/java/org/opensearch/cache/common/tier/TieredSpilloverCacheStatsHolder.java

@@ -43,6 +43,8 @@ public class TieredSpilloverCacheStatsHolder extends DefaultCacheStatsHolder {
     /** Dimension value for on-disk cache, like EhcacheDiskCache. */
     public static final String TIER_DIMENSION_VALUE_DISK = "disk";
 
+    static final List<String> TIER_VALUES = List.of(TIER_DIMENSION_VALUE_ON_HEAP, TIER_DIMENSION_VALUE_DISK);
+
     /**
      * Constructor for the stats holder.
      * @param originalDimensionNames the original dimension names, not including TIER_DIMENSION_NAME
@@ -167,4 +169,17 @@ public void decrementItems(List<String> dimensionValues) {
     void setDiskCacheEnabled(boolean diskCacheEnabled) {
         this.diskCacheEnabled = diskCacheEnabled;
     }
+
+    @Override
+    public void removeDimensions(List<String> dimensionValues) {
+        assert dimensionValues.size() == dimensionNames.size() - 1
+            : "Must specify a value for every dimension except tier when removing from StatsHolder";
+        // As we are removing nodes from the tree, obtain the lock
+        lock.lock();
+        try {
+            removeDimensionsHelper(dimensionValues, statsRoot, 0);
+        } finally {
+            lock.unlock();
+        }
+    }
 }