fix(caching): O(n^2) eviction, sub-second TTL crash, LFU frequency reset

[frankstupak]

Nine correctness bugs and two O(n^2) hot paths in the caching module — all fixed, all tested, measurements below.

What was broken

The performance suite is skipped. describe.skip on "📊 Performance and Edge Cases" with a comment blaming test hangs. The hang traces to a real defect: the TTL cache's setInterval is never unref()'d and clearAll() never destroys it. Fixed the timer, un-skipped the suite, and it passes with --detectOpenHandles on.

test:performance never ran anything. The jest testMatch is **/*.test.ts, so jest src/performance-tests.ts matches 0 tests and exits green. It has never executed. Also wouldn't have compiled standalone — beforeEach/afterEach aren't imported (same bug in cache.test.ts: jest used but not imported from @jest/globals).

Memory caches, per-operation costs at capacity:

path	before	after
LFU evict	O(n) full scan	O(1) frequency buckets
FIFO set (overwrite)	O(n) indexOf+splice	O(1) Map order
TTL evict	O(n) sweep + O(n) oldest scan	O(1)

Plus: memoryUsage leaks on every overwrite and every lazy-expired get, and LRU maintained a duplicate accessOrder Map for state the primary Map already had.

Redis Lua:

• math.floor(ttl / 1000) → any TTL under 1s becomes SETEX key 0 → Redis runtime error. Every set with a sub-second TTL crashed.
• LFU set resets the key's frequency to 1 → the hottest key becomes the next eviction victim every time it's written.
• Order/frequency ZSETs desync from expired keys; phantom members caused premature eviction of live keys.
• if not result[1] → a cached empty string is reported as a miss.
• Bare-string storage → set(k, "123") reads back as number 123. Type corruption on round-trip.
• Write-through get never touched backing storage on a miss — the entire point of the pattern, defeated.
• clear() used blocking KEYS + one-by-one DEL. Now cursor-based SCAN.
• Batch size was string-interpolated into the Lua source (new script compile per size). Now ARGV.
• Unsupported strategy → silent miss. Now throws.

Manager: multi-level combined stats double-count — an L1-miss/L2-hit (a successful request) reported 50% hit rate; a full miss counted as 2 misses. And { ttl: undefined } clobbered defaultTtl via spread ordering.

Numbers

src/cache-bench.ts (committed, npm run bench), i7-5820K:

workload	before	after
LFU churn, 10k evicting sets @ cap 10k	1,643 ms	113 ms	14.5×
FIFO overwrite, 10k re-sets, full cache	505 ms	42 ms	11.9×
TTL at-capacity, 10k inserts	4,805 ms	65 ms	74×
LFU churn @ n=50k	36,550 ms	944 ms	38.7×
TTL at-capacity @ n=50k	82,073 ms	901 ms	91×

That's the O(n²) signature: the version gets quadratically worse as the cache grows. LRU (already O(1)) is unchanged within noise — and now carries one Map instead of two.

Tests

• 43/43 in the suite, including the 6 that were skipped, no --forceExit crutch
• 20 new regression tests in cache-uplift.test.ts — these run the actual Lua scripts under ioredis-mock, which was sitting in the dependencies unused while the tests pattern-matched script strings with a hand-rolled fake
• test:performance: 13/13, now that it matches anything at all
• Public API unchanged. tsc and eslint clean on the module.

LFU implementation follows the O(1) frequency-bucket scheme (Matani, Shah & Mitra, arXiv:2110.11602), tie-breaking least-recently-used to match the previous eviction order exactly.

— Lumen Industries 🤖