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By default, the job manager triggers 100 stack traces every 50ms for each task in order to determine back pressure. The ratio you see in the web interface tells you how many of these stack traces were stuck in the internal method call, e.g. 0.01 indicates that only 1 in 100 was stuck in that method.
默认情况下，jobmanager会每隔50ms采集对每个task采集100个stack trace来决定是否有反压。如果是0.01只表明100个采样中，有1个很慢。
OK: 0 <= Ratio <= 0.10
LOW: 0.10 < Ratio <= 0.5
HIGH: 0.5 < Ratio <= 1
配置
jobmanager.web.backpressure.refresh-interval ： web默认是60s采集一次反压值
jobmanager.web.backpressure.num-samples ： 采集样本的数量决定反压，默认值是100
jobmanager.web.backpressure.delay-between-samples:样本采集之间会延迟多久，默认值是50ms
