[GitHub] [arrow] rymurr commented on a change in pull request #7326: ARROW-9010: [Java] Framework and interface changes for RecordBatch IPC buffer compression

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rymurr commented on a change in pull request #7326:
URL: https://github.com/apache/arrow/pull/7326#discussion_r435803219



##########
File path: java/vector/src/main/java/org/apache/arrow/vector/compression/CompressionCodec.java
##########
@@ -0,0 +1,68 @@
+/*
+ * 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.arrow.vector.compression;
+
+import org.apache.arrow.memory.ArrowBuf;
+
+/**
+ * The codec for compression/decompression.
+ */
+public interface CompressionCodec {
+
+  /**
+   * Given a buffer, estimate the compressed size.
+   * Please note this operation is optional, and some compression methods may not support it.
+   *
+   * @param input the input buffer to be estimated.
+   * @return the estimated size of the compressed data.
+   */
+  long estimateCompressedSize(ArrowBuf input);

Review comment:
       In the vector loader/unloader the estimated size is only needed by the compress/decompress methods. Is there a further use case where this would need to be externalised? Would simply compress/decompress be ok?

##########
File path: java/vector/src/main/java/org/apache/arrow/vector/compression/CompressionUtility.java
##########
@@ -0,0 +1,56 @@
+/*
+ * 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.arrow.vector.compression;
+
+import org.apache.arrow.flatbuf.BodyCompressionMethod;
+import org.apache.arrow.flatbuf.CompressionType;
+import org.apache.arrow.vector.ipc.message.ArrowBodyCompression;
+
+/**
+ * Utilities for data compression/decompression.
+ */
+public class CompressionUtility {
+
+  private CompressionUtility() {
+  }
+
+  /**
+   * Creates the {@link ArrowBodyCompression} object, given the {@link CompressionCodec}.
+   */
+  public static ArrowBodyCompression createBodyCompression(CompressionCodec codec) {
+    if (codec == null) {
+      return null;
+    }
+    for (int i = 0; i < CompressionType.names.length; i++) {
+      if (CompressionType.names[i].equals(codec.getCodecName())) {

Review comment:
       I feel like a switch statement and/or enum (similar to Type/ArrowType conversions would be better here than a tight loop of string comparisons. Not a huge deal as its a small array but I think its a bit easier to read.

##########
File path: java/vector/src/main/java/org/apache/arrow/vector/ipc/message/MessageSerializer.java
##########
@@ -300,6 +307,20 @@ public static long writeBatchBuffers(WriteChannel out, ArrowRecordBatch batch) t
     return out.getCurrentPosition() - bufferStart;
   }
 
+  /**
+   * Serialize the compression body.
+   */
+  public static long writeCompressionBody(
+      WriteChannel out, ArrowBodyCompression bodyCompression) throws IOException {
+    long bufferStart = out.getCurrentPosition();
+    ByteBuffer buf = ByteBuffer.allocate(2);

Review comment:
       I wonder if rather than allocating a new ByteBuffer it might be easier to just use a byte[] and the `write(byte[])` method. Potentially you could then use a byte[] to store the data in `ArrowBodyCompression` so that you don't have to allocate anything while writing the message.




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