steveniemitz opened a new pull request, #17783:
URL: https://github.com/apache/beam/pull/17783
This PR adds a new interface, `ShuffleCompressor`, which allows users to
plug in compression for values just before they're written to shuffle.
The interface is a little odd, we originally had exposed it as simply
wrapping Input/Output streams. However, this interface is much more efficient:
- In the compression path, the implementor can use the RandomAccessData as
both a buffer pool (using scratch space at the end for example) and also
compress the data "in place" if possible. Additionally, many compression
algorithms can operate more efficiently on a fixed-sized buffer rather than
having to deal with an unknown amount of input data.
- In the decompression path, using ByteBuffer allows efficiently slicing the
input and output buffers as well. Ideally I think this interface would use
ByteString as well, but didn't want to expose the shaded protobuf library in
the public API.
Additionally this also changes most places in the shuffle IO path to use
ByteString rather than byte[]. This allows efficiently "slicing" the buffer
received from the shuffle reader, removing a significant number of byte[]
copies.
Internally we have an implementation of ShuffleCompressor that uses zstd,
and we see a significant benefit from using it. For example, at level 3 (the
default), a simple `read -> reshuffle -> do something` pipeline sees a 50%
reduction in data shuffled for our representative test datasets.
R: @lukecwik
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