[chaotic-good]

I think that compression is a must for the serialization library. Protobuf uses almost twice less memory than Cap'n Proto. Using an external compression is not an option in some cases. E.g. consider building tcp-server that communicates with thousands of clients simultaneously. Each client connection will have its own LZ4 context that should be heap allocated. I believe it's about 16KB per connection + buffers. This results in large memory consumption and a lot of random memory access and TLB misses.

[kentonv]

Cap'n Proto offers "packed" encoding which applies light compression (removing zero-valued padding bytes), brings it in-line with Protobuf, and ought to be much faster than the things Protobuf does for "compression" (varint is a very slow encoding!).

[chaotic-good]

I'm glad that I was wrong about it.