We've found in the process of implementing support for LZ4 decompression that the fast Java decoder library does not support all the features of the C++ library (dependendent blocks can't be read, and by default that is what the C++ code emits). The only library we found (Apache Commons) that seems to support the full specification is unusably slow because it doesn't directly support off-heap data.
I don't recall seeing a discussion on the merits of using LZ4 Frame vs LZ4 Block compression in the Arrow IPC format, so I'm not sure if there is a strong rationale for one versus the other. At this point I think for interoperability we have three options: 1. Specify in the specification that "independent" blocks must be used for LZ4_FRAME. 2. Add LZ4_BLOCK to the specification and prefer that over LZ4_FRAME 3. Provide our own Java implementation (either directly in Arrow or by providing a patch to another project) that supports dependent blocks. Any thoughts? Thanks, Micah
