Github user HeartSaVioR commented on a diff in the pull request: https://github.com/apache/storm/pull/2200#discussion_r126548655 --- Diff: docs/Metrics.md --- @@ -125,3 +126,193 @@ The [builtin metrics]({{page.git-blob-base}}/storm-client/src/jvm/org/apache/sto [BuiltinMetricsUtil.java]({{page.git-blob-base}}/storm-client/src/jvm/org/apache/storm/daemon/metrics/BuiltinMetricsUtil.java) sets up data structures for the built-in metrics, and facade methods that the other framework components can use to update them. The metrics themselves are calculated in the calling code -- see for example [`ackSpoutMsg`]({{page.git-blob-base}}/storm-client/src/jvm/org/apache/storm/executor/Executor.java). +#### Reporting Rate + +The rate at which built in metrics are reported is configurable through the `topology.builtin.metrics.bucket.size.secs` metric. If you set this too low it can overload the consumers +and some metrics consumers expect metrics to show up at a fixed rate or the numbers could be off, so please use caution when modifying this. + + +#### Tuple Counting Metrics + +There are several different metrics related to counting what a bolt or spout does to a tuple. These include things like emitting, transferring, acking, and failing of tuples. + +In general all of these tuple count metrics are randomly sub-sampled unless otherwise state. This means that the counts you see both on the UI and from the built in metrics are not necessarily exact. In fact by default we sample only 5% of the events and estimate the total number of events from that. The sampling percentage is configurable per topology through the `topology.stats.sample.rate` config. Setting it to 1.0 will make the counts exact, but be aware that the more events we sample the slower your topology will run (as the metrics are counted on the critical path). This is why we have a 5% sample rate as the default. --- End diff -- I don't think we introduce 'critical path' anywhere in Storm but we already know about that. Isn't it widely-used word? If there's more widely-used representation we may be better to change.
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