[GitHub] [incubator-hudi] n3nash commented on a change in pull request #1077: [HUDI-335] : Improvements to DiskbasedMap

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n3nash commented on a change in pull request #1077: [HUDI-335] : Improvements to DiskbasedMap
URL: https://github.com/apache/incubator-hudi/pull/1077#discussion_r365049776
 
 

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 File path: hudi-common/src/main/java/org/apache/hudi/common/util/BufferedRandomAccessFile.java
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+/**
+ * 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.hudi.common.util;
+
+import org.apache.log4j.Logger;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+
+/**
+ * Use a private buffer for the read/write/seek operations of the RandomAccessFile
+ * to reduce the number of disk operations.
+ *
+ *                S    C   L/E
+ * Buffer:        |----+---|
+ *  File:  +---------------D-------------------+
+ *     S. startPosition - file position of start of the buffer.
+ *     C. currentPosition - file position of current pointer in the buffer.
+ *     L. validLastPosition - file position of the last byte in the buffer. (This is same as
+ *        endPosition of the buffer. Except for the last file block).
+ *                                              S-C--L--E
+ *                                                    (A)
+ *        Buffer:                               |-+--+--|
+ *        File:  +-----------------------------------D
+ *     E. endPosition() - end file position of the current buffer.
+ *     D. DiskPosition - Position in the file pointed by underlying RandomAccessFile.
+ *        When reading from the file, diskPosition aligns with startPosition.  When writing to
+ *        the file, diskPosition(D) aligns with validLastPosition(L/E).
+ *
+ *     A. AvailableSpace - Space between validLastPosition(L) and EndPosition(E)
+ *        is the available space in buffer, when writing/appending records
+ *        into the buffer/file.
+ *
+ *  Note: Based on BufferedRandomAccessFile implementation in Apache/Cassandra.
+ *  Author: Balajee Nagasubramaniam.
 
 Review comment:
   Please remove the author, we don't add that for any of the files. Also, please cite the original implementation similar to how is done here : https://github.com/apache/incubator-hudi/blob/master/hudi-hadoop-mr/src/main/java/org/apache/hudi/hadoop/hive/HoodieCombineHiveInputFormat.java#L80

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