I was looking into the memory usage of shuffle and one annoying thing is the default compression codec (LZF) is that the implementation we use allocates buffers pretty generously. I did a simple experiment and found that creating 1000 LZFOutputStream allocated 198976424 bytes (~190MB). If we have a shuffle task that uses 10k reducers and 32 threads running currently, the memory used by the lzf stream alone would be ~ 60GB.
In comparison, Snappy only allocates ~ 65MB for every 1k SnappyOutputStream. However, Snappy's compression is slightly lower than LZF's. In my experience, it leads to 10 - 20% increase in size. Compression ratio does matter here because we are sending data across the network.