Unable to adjust buffer size passed to compress (zlib) in HDFS

[Bill Strahm <bs...@xilinx.com>]

Hello,
Working with HDFS and zlib compression, I am trying to change the buffer size passed into the top of the libz.so implementation.

Our understanding is this should be changed with the parameter io.file.buffer.size.  The default is 64K and no matter how we change this parameter the buffer passed to libz.so is set to 64k.  At present, the io.file.buffer.size seems to control only CompressorStream buffer size but divides that into 64KB size buffers and sends only 64KB for compression. We should allow that to be controlled by io.file.buffer.size or else provide another parameter to control that
We found in ZlibCompressor.java the following constructor was being called

  public ZlibCompressor(Configuration conf) {
    this(ZlibFactory.getCompressionLevel(conf),
         ZlibFactory.getCompressionStrategy(conf),
         CompressionHeader.DEFAULT_HEADER,
         DEFAULT_DIRECT_BUFFER_SIZE);

DEFAULT_DIRECT_BUFFER_SIZE is set to 64 * 1024.  That said when we changed this constant, the value passed to libz.so was changed.

I believe the correct final line should be
conf.getInt("io.file.buffer.size", DEFAULT_DIRECT_BUFFER_SIZE));

possibly use io.compression.codec.zstd.buffersize and  IO_COMPRESSION_CODEC_ZSTD_BUFFER_SIZE_DEFAULT or does that control something else?

It looks like snappy correctly uses a configuration parameter:
(SnappyCodec.java)
    int bufferSize = conf.getInt(
        CommonConfigurationKeys.IO_COMPRESSION_CODEC_SNAPPY_BUFFERSIZE_KEY,
        CommonConfigurationKeys.IO_COMPRESSION_CODEC_SNAPPY_BUFFERSIZE_DEFAULT);

I would like to open a jira ticket for this, however being VERY new to the community - thought I had better check some assumptions first.

Bill
BILL STRAHM
Strategic Application Engineer

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