Add javadocs for FullFileCachedIndexInput

Signed-off-by: Shreyansh Ray <rayshrey@amazon.com>

Author: rayshrey

server/src/internalClusterTest/java/org/opensearch/remotestore/WritableWarmIT.java

@@ -31,7 +31,6 @@
 import org.opensearch.node.Node;
 import org.opensearch.test.InternalTestCluster;
 import org.opensearch.test.OpenSearchIntegTestCase;
-import org.opensearch.test.junit.annotations.TestLogging;
 
 import java.util.Arrays;
 import java.util.HashSet;
@@ -44,7 +43,7 @@
 @ThreadLeakFilters(filters = CleanerDaemonThreadLeakFilter.class)
 @OpenSearchIntegTestCase.ClusterScope(scope = OpenSearchIntegTestCase.Scope.TEST, numDataNodes = 0, supportsDedicatedMasters = false)
 // Uncomment the below line to enable trace level logs for this test for better debugging
-@TestLogging(reason = "Getting trace logs from composite directory package", value = "org.opensearch.index.store:TRACE")
+// @TestLogging(reason = "Getting trace logs from composite directory package", value = "org.opensearch.index.store:TRACE")
 public class WritableWarmIT extends RemoteStoreBaseIntegTestCase {
 
     protected static final String INDEX_NAME = "test-idx-1";
@@ -69,8 +68,8 @@ protected Settings featureFlagSettings() {
     public void testWritableWarmFeatureFlagDisabled() {
         Settings clusterSettings = Settings.builder().put(super.nodeSettings(0)).put(FeatureFlags.TIERED_REMOTE_INDEX, false).build();
         InternalTestCluster internalTestCluster = internalCluster();
-        internalTestCluster.startClusterManagerOnlyNodes(3, clusterSettings);
-        internalTestCluster.startDataOnlyNodes(1, clusterSettings);
+        internalTestCluster.startClusterManagerOnlyNode(clusterSettings);
+        internalTestCluster.startDataOnlyNode(clusterSettings);
 
         Settings indexSettings = Settings.builder()
             .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)

server/src/main/java/org/opensearch/index/store/remote/filecache/CachedFullFileIndexInput.java

@@ -16,7 +16,7 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
- * Implementation of the CachedIndexInput for NON_BLOCK files which takes in an IndexInput as parameter
+ * Implementation of the CachedIndexInput for full files which takes in an IndexInput as parameter
  *
  * @opensearch.experimental
  */

server/src/main/java/org/opensearch/index/store/remote/filecache/FullFileCachedIndexInput.java

@@ -12,12 +12,21 @@
 import org.apache.logging.log4j.Logger;
 import org.apache.lucene.store.AlreadyClosedException;
 import org.apache.lucene.store.IndexInput;
+import org.opensearch.common.annotation.ExperimentalApi;
 
 import java.io.IOException;
 import java.nio.file.Path;
 import java.util.HashSet;
 import java.util.Set;
 
+/**
+ * Extension of {@link FileCachedIndexInput} for full files for handling clones and slices
+ * We maintain a clone map so that we can close them when the parent IndexInput is closed so that ref count is properly maintained in file cache
+ * Closing of clones explicitly is needed as Lucene does not guarantee that it will close the clones
+ * https://github.com/apache/lucene/blob/8340b01c3cc229f33584ce2178b07b8984daa6a9/lucene/core/src/java/org/apache/lucene/store/IndexInput.java#L32-L33
+ * @opensearch.experimental
+ */
+@ExperimentalApi
 public class FullFileCachedIndexInput extends FileCachedIndexInput {
     private static final Logger logger = LogManager.getLogger(FullFileCachedIndexInput.class);
     private final Set<FullFileCachedIndexInput> clones;
@@ -31,6 +40,10 @@ public FullFileCachedIndexInput(FileCache cache, Path filePath, IndexInput under
         clones = new HashSet<>();
     }
 
+    /**
+     * Clones the index input and returns the clone
+     * Increase the ref count whenever the index input is cloned and add it to the clone map as well
+     */
     @Override
     public FullFileCachedIndexInput clone() {
         FullFileCachedIndexInput clonedIndexInput = new FullFileCachedIndexInput(cache, filePath, luceneIndexInput.clone(), true);
@@ -39,6 +52,10 @@ public FullFileCachedIndexInput clone() {
         return clonedIndexInput;
     }
 
+    /**
+     * Clones the index input and returns the slice
+     * Increase the ref count whenever the index input is sliced and add it to the clone map as well
+     */
     @Override
     public IndexInput slice(String sliceDescription, long offset, long length) throws IOException {
         if (offset < 0 || length < 0 || offset + length > this.length()) {
@@ -62,6 +79,10 @@ public IndexInput slice(String sliceDescription, long offset, long length) throw
         return slicedIndexInput;
     }
 
+    /**
+     * Closes the index input and it's clones as well
+     * @throws IOException
+     */
     @Override
     public void close() throws IOException {
         if (!closed) {