Kqr Row Cache Contention Check Gets -

— KQR’s row cache for item:42 expired. 9:00:02 — 10,000 concurrent GET requests arrived simultaneously.

She hot-patched KQR’s logic to use :

CACHE GETS (total): 10,000 CACHE HITS: 0 CACHE MISSES: 10,000 MISSES WHILE LOCK HELD: 10,000 CONTENTION RATIO: 1.00 TOP CONTENDED ROW: item:42 WAITING THREADS: 9,999 LOCK HOLD TIME (avg): 487ms This was a contention storm . The first thread to acquire the cache lock went to the database (487ms). The other 9,999 threads didn’t just wait — they spun, retried, and choked the CPU. kqr row cache contention check gets