PingCAP Style Guide

Guide to writing idiomatic code at PingCAP and in the TiKV project.

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Performance

• “Premature optimization is the root of all evil”
  • Optimisation should be justified by profiles and benchmarks.
  • Prefer to write simple, clear code unless optimisation is necessary.
• Don’t write sloppy code:
  • Avoid unnecessary allocation and copying.
  • Use iterators.
  • Don’t use Arc or Mutex for single-threaded code (use Rc or RefCell instead).
  • Avoid global, mutable state.
  • Prefer to use push and push_str to build strings in performance-sensitive code, rather than the format macro.
  • Don’t worry about empty Vecs/Strings - they don’t allocate and are very cheap.
  • Consider the computational complexity of algorithms, but bear in mind the expected size of input.
• Don’t hide potentially expensive code
  • code that may do IO, block, or sleep should be clearly named and documented.
  • allocation should be either expected from the purpose of a function or be documented (e.g., conversion functions should not allocate).

The concurrency of your code is likely to have a large impact on its performance. Consider if and how code can be concurrent at the design phase. Design to avoid locking or other forms of synchronisation if code is performance-sensitive.

Rationale

• Modern compilers and CPUs can optimize simple code more effectively than complicated code; modern CPUs are complex, it is very difficult to predict whether hand-optimised code is effective.
• Allocation is a primary cause of slowdown in many programs.
• Use iterators to avoid slow bounds checks.
• Don’t surprise clients of your code.
• Performant code requires scaling to multiple threads, blocking threads on locks, IO, etc., kills parallelism.

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