Proposal: Significant performance improvements for Data.Map
Milan Straka's recent Haskell Symposium paper (PDF) shed light on the containers:Data.Map library, indicating there were both algorithmic and stylistic performance improvements to be made.
This proposal provides a patch that dramatically improves performance across the API. Three standard techniques are applied to the code:
- Worker/Wrapper transformations of recursive functions with constant arguments (aka. the static argument transformation).
- Explicit inlining of wrapper functions.
- Explicit strictness of keys to functions.
Three complementary, but orthogonal patches are provided.
- Add a testsuite, with coverage data (currently 91% of top level functions, and all core functions).
- Add a micro-benchmark suite based on Criterion, for empirical evidence of improvements to each function.
- The optimization patch itself.
All 3 patches should be applied, under this proposal.
The benchmark results are very strong:
- An average speedup across the core api of 47% (on intel i7 / linux 64 bit), and;
- 36% on Mac / intel core 2 duo 32 bit).
No bugs were identified in the development of the comprehensive testsuite, which includes a large set of unit tests from Kazu Yamamoto
A fork of the containers package, with the 3 patches (and a version bump to make it easier to test out) is available:
Separately, the patches are attached to this ticket.
The consideration period is 3 weeks (before ICFP).
Work carried out over 28/29th August, 2010 in Utrecht, NL, by Johan Tibell and Don Stewart.