Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/19222#discussion_r172356146 --- Diff: common/unsafe/src/main/java/org/apache/spark/unsafe/memory/OnHeapMemoryBlock.java --- @@ -0,0 +1,141 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.spark.unsafe.memory; + +import org.apache.spark.unsafe.Platform; + +/** + * A consecutive block of memory with a long array on Java heap. + */ +public final class OnHeapMemoryBlock extends MemoryBlock { --- End diff -- So the basic idea is, `OnHeapMemoryBlock` and `OffHeapMemoryBlock` are the major memory blocks that should be used inside Spark, returned by the memory manager according to the memory mode. `ByteArrayMemoryBlock` would only be used in some certain places where data is always `bye[]`, and the memory is not allocated from the memory manager. Hopefully we can always use memory returned by memory manager and track the memory usage, and eventually remove `ByteArrayMemoryBlock`.
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