Catwalk.jl Intro

Catwalk.jl can speed up long-running Julia processes by minimizing the overhead of dynamic dispatch. It is a JIT compiler that continuosly re-optimizes dispatch code based on data collected at runtime.

Speedup demo source code of this test

It profiles user-specified call sites, estimating the distribution of dynamically dispatched types during runtime, and generates fast static routes for the most frequent ones on the fly.

The statistical profiler has very low overhead and can be configured to handle situations where the distribution of dispatched types changes relatively fast.

To minimize compilation overhead, recompilation only occurs when the distribution changed enough and the tunable cost model predicts significant speedup compared to the best version that was previously compiled.

When to use this package

The dynamic dispatch in Julia is very fast in itself, so speeding it up is not an easy task. Catwalk.jl focuses on use cases when it is not feasible to list the dynamically dispatched concrete types in the source code of the call site.

Catwalk.jl assumes the followings:

  • The process is long running: several seconds, but possibly minutes are needed to break even after the initial compilation overhead.
  • Few dynamically dispatched call sites contribute significantly to the running time (dynamic dispatch in a hot loop).
  • You can modify the source code around the interesting call sites (add a macro call), and calculation is organized into batches.