Small-size data serialization problem

[yunhua-deng]

According to our experiments, if the size of the raw message is less than 200 bytes, cap'proto gets slower than protobuf. The reason could be the overhead taken by the malloc process invovled in the deserializing each message?

[yunhua-deng]

Actually, we are benchmarking the c-capnproto, and seeing that in deserilization there is some malloc overhead, https://github.com/opensourcerouting/c-capnproto/blob/master/tests/example-test.cpp#L98

For 4000000 messages with each of about 200 bytes in size, the serilization/deserilization times are as follows:

protobuf: 650/750ms
capnp: 280ms
c-capnp: 500/900ms

FYI: We have fired an issue in c++ capnproto
capnproto/capnproto#790 (comment)