Allocation churn on generators

Tue, 07 Oct 2025 21:16:10 +0000

When generating moderately large values there is some LazySeq churn that could be avoided. For example, the following snippet allocates over 15GB (measured with async-profiler):

(core/let [g (vector (not-empty string-alphanumeric) 1000 5000)]
  (time
   (dotimes [seed 50]
     (dorun (generate g 100 seed)))))

The pattern of generating multiple (increasingly larger) values is common with quick-check (via deftest et al).

Many generators are built on top of choose, and there is an opportunity to reduce churn by special casing shrink-int for longs (which should be the common case compared to big ints).

I have a patch that decreases total allocations of the repro above by ~15% and speed up the run time by ~25% (measured on jdk 25, with -Xmx512m -XX:+UseSerialGC to decrease variance). Happy to share it.

Let RoseTree satisfy (implement) Datafiable

Thu, 02 Jul 2020 18:36:54 +0000

I think for debugging it would be awesome to be able to navigate through the rose trees.

Clojure Q&A - Questions without answers in test.check

Allocation churn on generators

Let RoseTree satisfy (implement) Datafiable