Sampling
Adding Sentry to your app gives you a great deal of very valuable information about errors and performance you wouldn't otherwise get. And lots of information is good -- as long as it's the right information, at a reasonable volume.
To send a representative sample of your errors to Sentry, set the sampleRate
option in your SDK configuration to a number between 0
(0% of errors sent) and 1
(100% of errors sent). This is a static rate, which will apply equally to all errors. For example, to sample 25% of your errors:
Sentry.init({ sampleRate: 0.25 });
The error sample rate defaults to 1
, meaning all errors are sent to Sentry.
Changing the error sample rate requires re-deployment. In addition, setting an SDK sample rate limits visibility into the source of events. Setting a rate limit for your project (which only drops events when volume is high) may better suit your needs.
Whatever a transaction's sampling decision, that decision will be passed to its child spans and from there to any transactions they subsequently cause in other services.
(See Distributed Tracing for more about how that propagation is done.)
If the transaction currently being created is one of those subsequent transactions (in other words, if it has a parent transaction), the upstream (parent) sampling decision will be included in the sampling context data. Your tracesSampler
can use this information to choose whether to inherit that decision. In most cases, inheritance is the right choice, to avoid breaking distributed traces. A broken trace will not include all your services.
tracesSampler: samplingContext => {
// always inherit
if (samplingContext.parentSampled !== undefined) {
return samplingContext.parentSampled
}
...
// rest of sampling logic here
}
If you're using a tracesSampleRate
rather than a tracesSampler
, the decision will always be inherited.
There are multiple ways for a transaction to end up with a sampling decision.
- Random sampling according to a static sample rate set in
tracesSampleRate
- Random sampling according to a sample function rate returned by
tracesSampler
- Absolute decision (100% chance or 0% chance) returned by
tracesSampler
- If the transaction has a parent, inheriting its parent's sampling decision
- Absolute decision passed to
startTransaction
When there's the potential for more than one of these to come into play, the following precedence rules apply:
- If a sampling decision is passed to
startTransaction
, that decision will be used, overriding everything else. - If
tracesSampler
is defined, its decision will be used. It can choose to keep or ignore any parent sampling decision, use the sampling context data to make its own decision, or choose a sample rate for the transaction. We advise against overriding the parent sampling decision because it will break distributed traces) - If
tracesSampler
is not defined, but there's a parent sampling decision, the parent sampling decision will be used. - If
tracesSampler
is not defined and there's no parent sampling decision,tracesSampleRate
will be used.
Our documentation is open source and available on GitHub. Your contributions are welcome, whether fixing a typo (drat!) or suggesting an update ("yeah, this would be better").