How Much Does Redis MONITOR Slow Down Your Server? Benchmark Results Revealed
A benchmark comparing Redis performance with and without the MONITOR command shows a substantial drop in throughput—up to 53% for SET operations—highlighting that MONITOR should be used only for short‑term debugging, as illustrated by a real‑world Meituan case study.
Previously introduced Redis MONITOR, this article tests its performance impact.
Test Process
Using redis-benchmark with 10 clients and 100,000 requests, we measured throughput before and after enabling MONITOR. redis-benchmark -c 10 -n 100000 -q Results without MONITOR:
PING_INLINE: 92506.94 requests per second
PING_BULK: 97943.19 requests per second
SET: 94786.73 requests per second
GET: 99403.58 requests per second
INCR: 89766.61 requests per secondResults with MONITOR enabled:
PING_INLINE: 76569.68 requests per second
PING_BULK: 67294.75 requests per second
SET: 44404.97 requests per second
GET: 60132.29 requests per second
INCR: 49382.71 requests per secondComparison: Enabling MONITOR reduces throughput significantly, e.g., SET drops by 53%, GET by 39%, INCR by 44%.
Real‑world Case
Meituan experienced memory spikes in a Redis cluster shard. Investigation showed an unusually high client_longest_output_list value, indicating large output buffers.
Using client list, they found a client with the cmd field set to monitor , confirming that a long‑running MONITOR caused the performance degradation.
The findings demonstrate that MONITOR should only be used for short‑term debugging, not for continuous monitoring.
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