16 Nov 2013
Below I describe the results of a performance comparison between capnproto-rust and the definitive C++ implementation.
To perform the comparison, I reimplemented in Rust the three benchmark cases included with capnproto-c++. Each case consists of some communications between a client and a server, with nontrivial computation taking place at both ends.
Within each case, there are five possible modes of communication. The simplest is “object”, in which the sender directly passes an in-memory object. In “bytes”, the sender writes its message to a byte buffer, which it then passes directly. In “pipe”, the sender writes its message as bytes over a pipe to another process. In the “packed” versions of “bytes” and “pipe”, the sender applies Cap’n Proto standard packing to the raw bytes before sending.
The “carsales” case emphasizes records with many numeric fields. For each communication mode, I ran 10000 iterations, resulting in a throughput of about 125 MB unpacked, or 81 MB packed.
Here capnproto-rust is roughly even with capnproto-c++ except for the cases where it has to do I/O, in which case relative performance degrades slightly.
The “catrank” emphasizes string processing. I ran 1000 iterations for each mode, resulting in a throughput of about 206 MB unpacked, or 186 MB packed.
Here capnproto-rust’s relative performance is fairly consistent, and a bit worse than in the “carsales” case. I believe the main reason for this is that capnproto-rust is doing extra string copies to get around the fact that I have not yet implemented direct writing for string fields.
The “eval” case emphasizes nested structures. I ran 200000 iterations for each mode, resulting in a throughput of about 262 MB unpacked, or 80 MB packed.
Here we see capnproto-rust’s relative performance degrade significantly when it must perform I/O. I am uncertain why this degradation occurs, though it seems to be related to the size of the messages. Unpacked, the total size of a single “eval” request plus a single “eval” response is about 1 KB, compared to the averages of about 12 KB in the “carsales” case and about 200 KB in the “catrank” case.
