swamirishi commented on code in PR #9549:
URL: https://github.com/apache/ozone/pull/9549#discussion_r2648590894
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hadoop-hdds/managed-rocksdb/src/main/java/org/apache/hadoop/hdds/utils/db/managed/ManagedDirectSlice.java:
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@@ -17,98 +17,34 @@
package org.apache.hadoop.hdds.utils.db.managed;
-import static org.apache.hadoop.hdds.utils.db.managed.ManagedRocksDB.NOT_FOUND;
-
-import com.google.common.annotations.VisibleForTesting;
import java.nio.ByteBuffer;
-import org.apache.hadoop.hdds.utils.db.RocksDatabaseException;
-import org.apache.ratis.util.function.CheckedConsumer;
-import org.apache.ratis.util.function.CheckedFunction;
import org.rocksdb.DirectSlice;
-import org.rocksdb.RocksDBException;
/**
- * ManagedDirectSlice is a managed wrapper around the DirectSlice object. It
ensures
- * proper handling of native resources associated with DirectSlice, utilizing
- * the ManagedObject infrastructure to prevent resource leaks. It works in
tandem
- * with a ByteBuffer, which acts as the data source for the managed slice.
+ * ManagedDirectSlice is a class that extends the {@link DirectSlice} class
and provides additional
+ * management for slices of direct {@link ByteBuffer} memory. This class
initializes the slice with
+ * the given ByteBuffer and sets its prefix and length properties based on the
buffer's position
+ * and remaining capacity.
+ *
+ * The class is designed to handle specific memory slicing operations while
ensuring that the
+ * provided ByteBuffer’s constraints are respected. ManagedDirectSlice
leverages its parent
+ * {@link DirectSlice} functionalities to deliver optimized direct buffer
handling.
+ *
+ * Constructor:
+ * - Initializes the ManagedDirectSlice instance with a provided ByteBuffer.
+ * - Sets the slice length to the buffer's remaining capacity.
+ * - Removes the prefix based on the buffer's position.
*
- * This class overrides certain operations to tightly control the lifecycle and
- * behavior of the DirectSlice it manages. It specifically caters to use cases
- * where the slice is used in RocksDB operations, providing methods for safely
- * interacting with the slice for put-like operations.
+ * NOTE: This class should be only with ByteBuffer whose position and limit is
going be immutable in the lifetime of
+ * this ManagedDirectSlice instance. This means that the ByteBuffer's
position and limit should not be modified
+ * externally while the ManagedDirectSlice is in use. The value in the byte
buffer should be only accessed via the
+ * instance.
*/
-public class ManagedDirectSlice extends ManagedObject<DirectSlice> {
-
- private final ByteBuffer data;
+public class ManagedDirectSlice extends DirectSlice {
Review Comment:
Look at the code here:
DirectSlice initialization :
https://github.com/facebook/rocksdb/blob/0bf9079d44eea91afda7151306d3a3439a39511b/java/rocksjni/slice.cc#L292-L308
Slice initialization:
https://github.com/facebook/rocksdb/blob/0bf9079d44eea91afda7151306d3a3439a39511b/java/rocksjni/slice.cc#L130-L147
If you look at the code direct slice initialization just creates a slice
object by pointing to the already present directByteBuffer no copies. Whereas
the Slice initialization has copy from jbyte array to direct off heap memory
and then create a Slice object. The code execution just varies on the buffer
copy. So directSlice would always beat the Slice performance. Now it comes to
the overhead by how much which depends on the key length.
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