WHY YOUR REDIS IS SLOW: IT IS SINGLE THREADED AND YOU SENT IT KEYS

Summary from the TLDR Data newsletter

Redis executes commands on a single thread, so one expensive operation such as KEYS, FLUSHALL, a large DEL, or an unbounded collection read can block every client and cause sudden latency spikes even when CPU and network usage look normal. Use SLOWLOG and LATENCY tools to find offenders, replace full scans with cursor-based SCAN commands, use UNLINK for large deletions, shard oversized keys, and disable dangerous commands in production.