Github user vdiravka commented on a diff in the pull request:
https://github.com/apache/drill/pull/846#discussion_r120694784
--- Diff:
exec/java-exec/src/main/java/org/apache/parquet/hadoop/ParquetColumnChunkPageWriteStore.java
---
@@ -0,0 +1,269 @@
+/*
+ * 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.parquet.hadoop;
+
+import static
org.apache.parquet.column.statistics.Statistics.getStatsBasedOnType;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+import
org.apache.drill.exec.store.parquet.ParquetDirectByteBufferAllocator;
+import org.apache.parquet.bytes.BytesInput;
+import org.apache.parquet.bytes.CapacityByteArrayOutputStream;
+import org.apache.parquet.column.ColumnDescriptor;
+import org.apache.parquet.column.Encoding;
+import org.apache.parquet.column.page.DictionaryPage;
+import org.apache.parquet.column.page.PageWriteStore;
+import org.apache.parquet.column.page.PageWriter;
+import org.apache.parquet.column.statistics.Statistics;
+import org.apache.parquet.format.converter.ParquetMetadataConverter;
+import org.apache.parquet.hadoop.CodecFactory.BytesCompressor;
+import org.apache.parquet.io.ParquetEncodingException;
+import org.apache.parquet.schema.MessageType;
+import org.apache.parquet.bytes.ByteBufferAllocator;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This is a copy of ColumnChunkPageWriteStore from parquet library except
of OutputStream that is used here.
+ * Using of CapacityByteArrayOutputStream allows to use different
ByteBuffer allocators.
--- End diff --
I meant a special case regarding 20Gb. Usually 40 threads can be used in
sufficiently powerful machines with enough RAM space. But we can control the
memory usage by reducing number of threads per node to prevent OOM while
buffering data.
512Mb is the default `store.parquet.block-size`, but according [Drill
doc](https://drill.apache.org/docs/parquet-format/#configuring-the-size-of-parquet-files)
it is recommended to set this value to the number of bytes less than or equal
to the block size of MFS, HDFS, or the file system. Then only 320K will be
buffered in memory.
Nothing wrong with `BufferedOutputStream`. Original `ColumnChunkPageWriter`
uses it, but together with `ConcatenatingByteArrayCollector` (which can buffer
data only in `List<byte[]>`). I suppose it is possible to upgrade the last
class to use `ByteBuffers`, but the result will be similar to
`CapacityByteArrayOutputStream`.
As I understand, data buffering allows to write into the disk entire block
without going back and writing anything else, ideally one row group per one fs
block. Looks like it is suitable for HDFS as well.
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