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https://issues.apache.org/jira/browse/HADOOP-13578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15633647#comment-15633647
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Jason Lowe commented on HADOOP-13578:
-------------------------------------
Thanks for updating the patch! It's great to see compatibility between the
zstd CLI and the Hadoop codec.
I'm confused why the codec returns null for getCompressorType,
createCompressor, getDecompressorType, and createDecompressor. This is going
to break code that expects to wield the compressor/decompressor rather than
streams directly. I would expect it to work more like the DefaultCodec or
BZip2Codec where the codec returns appropriate Compressor and Decompressor
classes and leverages the existing CompressorStream, DecompressorStream, and
CompressionCodec.Util classes to handle the stream interfaces of Codec. For
example, the CompressorStream abstract class already handles the single-byte
write method, protection from double-finish and double-close, the
DecompressorStream already implemetns skip, etc.
The original approach used direct byte buffers, but the new patch no longer
does. All the other codecs leverage direct byte buffers, so I'm curious about
the reasoning for that change. I'm not a JVM expert, but I'm wondering if the
*PrimitiveArrayCritical methods have unfavorable impacts on other threads in
the JVM (e.g.: due to pausing GC or other effects). Given that
GetPrimitiveArrayCritical could trigger an array copy in order to perform it's
task and we have to copy the bytes from the output buffer into the output
stream anyway, I would expect direct byte buffers to be faster for at least the
output buffer case.
Speaking of double-finish, it looks like that could be problematic and lead to
double-free's in the native code layer. In addition to leveraging
CompressorStream/DecompressorStream as mentioned above to help with this, we
could zero the stream field after we are finished and check for a non-null
stream context before doing operations.
We should throw NPE if the caller passes a null for the source data buffer.
Similarly the native code should throw an error if it cannot obtain pointers to
the Java buffers. Currently it just silently returns no progress which will
result in an infinite loop in practice as it tries to reach the end of the
input and never gets there if the error keeps occurring on each JNI invocation.
The documentation for the zstd streaming interface mentions that flushing or
ending a stream may require multiple invocations in order to fully accomplish
the task, but I don't see corresponding loops in the java code to handle that
scenario:
{noformat}
* At any moment, it's possible to flush whatever data remains within buffer,
using ZSTD_flushStream().
* `output->pos` will be updated.
* Note some content might still be left within internal buffer if
`output->size` is too small.
* @return : nb of bytes still present within internal buffer (0 if it's empty)
* or an error code, which can be tested using ZSTD_isError().
*
* ZSTD_endStream() instructs to finish a frame.
* It will perform a flush and write frame epilogue.
* The epilogue is required for decoders to consider a frame completed.
* Similar to ZSTD_flushStream(), it may not be able to flush the full content
if `output->size` is too small.
* In which case, call again ZSTD_endStream() to complete the flush.
{noformat}
IOUtils.closeQuietly is being called on the output stream which could lead to
silent data corruption. If there was an issue writing out the last bits of
data as a result of the close call then this will silently eat the error. The
user is left with a "successful" operation that did not actually succeed.
The getLibraryName native method should do something sane for the non-UNIX
case, like returning the Unavailable string as some codecs do when they can't
compute it in the UNIX case. Bonus points for adding a WINDOWS case, and it
looks like we can model after the Windows implementations of getLibraryName in
the other codecs.
In the decompressor, why are we finished when we decode a frame? I thought it
was valid for a ZStandard compression stream to be made up of one or more
frames, so if there is more input after decoding a frame it seems like the
prudent thing to do is try decoding another frame.
It would be nice to allow the input and output buffer sizes to be configurable.
When used as part of wide merge sorts, there are going to be a lot of codec
instances. It may be necessary to use a smaller buffer size per codec to
reduce the merge's memory footprint due to all those codec I/O buffers. It
makes sense to use the library-recommended size as the default value, but it
should be straightforward to allow the user to override this.
Nit: srcSize is not really a size in the following code but rather a
terminating offset. Renaming it to something like endOffset would be more
clear, since we're comparing it against the inputBufferOffset. Same comment
for dstSize in the decompressor.
{code}
int srcSize = offset + len;
inputBufferOffset = offset;
while (inputBufferOffset < srcSize) {
{code}
Nit: The whitespace was removed around this line in the ASF license header, and
it would be good to restore it so it's consistent with the ASF headers in other
files.
{noformat}
* http://www.apache.org/licenses/LICENSE-2.0
{noformat}
> Add Codec for ZStandard Compression
> -----------------------------------
>
> Key: HADOOP-13578
> URL: https://issues.apache.org/jira/browse/HADOOP-13578
> Project: Hadoop Common
> Issue Type: New Feature
> Reporter: churro morales
> Assignee: churro morales
> Attachments: HADOOP-13578.patch, HADOOP-13578.v1.patch,
> HADOOP-13578.v2.patch
>
>
> ZStandard: https://github.com/facebook/zstd has been used in production for 6
> months by facebook now. v1.0 was recently released. Create a codec for this
> library.
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