If the GC reclaims a keyword, any subsequent attempt to create a keyword requires an O(n) scan over the entire keyword table via Util.clearCache. This is a significant performance cost in keyword-heavy operations; e.g. JSON parsing.
Patch: keyword-cache.diff - patch to defer cleaning till portion of the table is dead and avoid multiple threads cleaning simultaneously.
Patch: kw-clean-future.patch - patch to spin cache cleaning into a future. Found that 1) this introduces some ordering constraints and circularity between Agent and Keyword (fixable) and 2) using the future pool for this means shutdown-agents would always need to be called (in the patch I avoided this by changing agent's soloExecutor to use daemon threads.
Patch: unified-kw-patch.diff - Alternative to keyword-cache and clean-future.patch. Combines all keyword-perf changes, including the EDN kw parser improvement, improved table lookup performance, and has threads cooperate to empty the table refqueue with a minimum of contention.