Divij Vaidya created KAFKA-15057:
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Summary: Use new interface
ZstdBufferDecompressingStreamNoFinalizer from zstd-jni
Key: KAFKA-15057
URL: https://issues.apache.org/jira/browse/KAFKA-15057
Project: Kafka
Issue Type: Sub-task
Components: core
Affects Versions: 3.6.0
Reporter: Divij Vaidya
Assignee: Divij Vaidya
Fix For: 3.6.0
h1. Background
In Kafka's code, every batch of records is stored in a in-memory byte buffer.
For compressed workload, this buffer contains data in compressed form. Before
writing it to the log, Kafka performs some validations such as ensuring that
offsets are monotonically increasing etc. To perform this validation, Kafka
needs to uncompress the data stored in byte buffer.
For zstd compressed batches, Kafka uses ZstdInputStreamNoFinalizer interface
provided by the downstream zstd-jni library to perform decompression.
ZstdInputStreamNoFinalizer takes input an InputStream and provides output an
InputStream. Since, Kafka stores the entire batch in a ByteBuffer, Kafka wraps
the ByteBuffer into an InputStream to satisfy the input contract for
ZstdInputStreamNoFinalizer.
h1. Problem
ZstdInputStreamNoFinalizer is not a good fit for our use case because we
already have the entire compressed data stored in a buffer. We don't have a
need for an interface which takes InputStream as an input. Our requirement is
for an interface which takes a ByteBuffer as an input and provides a stream of
uncompressed data as output. Prior to zstd-jni 1.5.5, no such interface
existed. Hence, we were forced to use ZstdInputStreamNoFinalizer.
Usage of ZstdInputStreamNoFinalizer has the following problems:
1. When decompression of batch is complete, we try to read another byte to
check if the actual batch size if equal to declared batch size. This is done at
RecordIterator#next(). This extra call to read another byte leads to a JNI call
in existing interface.
2. Since this interface requires input as a InputStream, we take the ByteBuffer
containing compressed batch and convert it into a InputStream. This interface
internally uses an intermediate buffer to read data from this InputStream in
chunks. The chunk size is determined by underlying zstd library and hence, we
will allocate a new buffer with very batch.
h1. Solution
I have extended an an interface in downstream library zstd-jni to suit the use
case of Kafka. The new interface is called
ZstdBufferDecompressingStreamNoFinalizer. It provides an interface where it
takes input as a ByteBuffer containing compressed data and provides output as
an InputStream. It solves the above problems as follows:
1. When we read the final decompressed frame, this interface sets a flag to
mark that all uncompressed data has been consumed. When RecordIterator#next()
tries to determine if the stream has ended, we simply read the flag and hence,
do not have to make a JNI call.
2. It does not require any buffer allocation for input. It takes the input
buffer and passes it across the JNI boundary without any intermediate copying.
Hence, we don't perform any buffer allocation.
h1. References
h2. Changes in downstream zstd-jni
Add new interface -
[https://github.com/luben/zstd-jni/commit/d65490e8b8aadc4b59545755e55f7dd368fe8aa5]
Bug fixes in new interface -
[https://github.com/luben/zstd-jni/commit/8bf8066438785ce55b62fc7e6816faafe1e3b39e]
[https://github.com/luben/zstd-jni/commit/100c434dfcec17a865ca2c2b844afe1046ce1b10]
[https://github.com/luben/zstd-jni/commit/355b8511a2967d097a619047a579930cac2ccd9d]
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