## series

There are two ways you can control sending to Sentry Of transactions The amount of .

## Uniform Sample Rate

If you wish transactions Of cross-section uniform , No matter where or under what circumstances you are in the application , And satisfied with the default inheritance and priority behavior described below , Setting a uniform sampling rate is a good choice .

So , Please put `Sentry.init()` Medium `tracesSampleRate` Option set to 0 To 1 A number between . After setting this option , Each created transaction There will be a percentage of opportunities sent to Sentry.（ therefore , for example , If you will `tracesSampleRate` Set to `0.2`, Will record and send about 20％ Of transactions.） As shown below ：

``````Sentry.init({
// ...
tracesSampleRate: 0.2,
});
``````

## Dynamic Sampling Function

If you meet the following conditions , The sampling function is a good choice ：

• Want to be different rates Sampling different transactions
• Want to filter out some completely transactions
• To modify the default priority and inheritance behavior described below

To do dynamic sampling , Please put `Sentry.init()` Medium `tracesSampler` Option is set to a function , This function will accept `samplingContext` Object and return 0 To 1 The sampling rate between . for example ：

``````Sentry.init({
// ...
tracesSampler: samplingContext => {
// Examine provided context data (including parent decision, if any) along
// with anything in the global namespace to compute the sample rate or
// sampling decision for this transaction
if ("...") {
// These are important - take a big sample
return 0.5;
} else if ("...") {
// These are less important or happen much more frequently - only take 1%
return 0.01;
} else if ("...") {
// These aren't something worth tracking - drop all transactions like this
return 0;
} else {
// Default sample rate
return 0.1;
}
};
});
``````

For convenience , This function can also return Boolean values . return `true` Equal to return to `1`, And guarantee that transaction Will be sent to Sentry. return `false` Equal to return to `0`, This will ensure that transaction Send to Sentry.

### Default Sampling Context Data

establish transaction when , Pass to `tracesSampler` Of `samplingContext` The information contained in the object varies by platform and integration .

For browser based SDK, It includes at least the following ：

``````// contents of `samplingContext`
{
transactionContext: {
name: string; // human-readable identifier, like "GET /users"
op: string; // short description of transaction type, like "pageload"
}
parentSampled: boolean; // if this transaction has a parent, its sampling decision
location: Location | WorkerLocation; // the window.location or self.location object
... // custom context as passed to `startTransaction`
}
``````

### Custom Sampling Context Data

Manually create transaction when , You can pass the data as an optional second parameter to `startTransaction` To add data to `samplingContext`. If you want the sampler to be accessible but don't want it to be `tags` or `data` Attach to transaction Data in （ For example, sensitive information or too large to follow transaction Messages sent ）, This will be very useful . for example ：

``````Sentry.startTransaction(
{
// `transactionContext` - will be recorded on transaction
name: 'Search from navbar',
op: 'search',
tags: {
testGroup: 'A3',
},
},
// `customSamplingContext` - won't be recorded
{
// PII
userId: '12312012',
// too big to send
resultsFromLastSearch: { ... }
},
);
``````

## Inheritance

No matter what transaction What is the sampling decision of , The decision will be passed on to child spans, And from there to any... That they subsequently cause in other services transactions.（ More about how to complete the dissemination , Please see the Connecting Backend and Frontend Transactions.）

If you are currently creating transaction It's the follow-up transactions One of （ let me put it another way , If it has a father transaction）, Then upstream （ Father ） Sampling decisions will always be included in the sampling context data , So that your `tracesSampler` Choose whether and when to inherit the decision .（ in the majority of cases , Inheritance is the right choice , So there's no partial tracking .）

In some SDK in , For convenience ,`tracesSampler` Function can return a Boolean value , such , If this is the expected behavior , You can return to the parent's decision directly .

``````tracesSampler: samplingContext => {
// always inherit
if (samplingContext.parentSampled !== undefined) {
return samplingContext.parentSampled
}
...
// rest of sampling logic here
}
``````

If you are using `tracesSampleRate` instead of `tracesSampler` , Then the decision will always be inherited .

## Forcing a Sampling Decision

If in transaction When you create it, you know if you want to transaction Send to Sentry, You can also choose to pass the sampling decision directly to transaction Constructors （ Please note that , be not in `customSamplingContext` In the object ）. If you do , be transaction Will not accept `tracesSampleRate` Constraints , And it won't run `tracesSampler`, So you can count on the decisions passed not to be covered .

``````Sentry.startTransaction({
name: "Search from navbar",
sampled: true,
});
``````

## Precedence

transaction There are many ways to make sampling decisions .

• Based on `tracesSampleRate` Random sampling at the static sampling rate set in
• according to `tracesSampler` Return the dynamic sampling rate for random sampling
• `tracesSampler` The absolute decision of return （100％ Opportunity or 0％ The opportunity to ）
• If transaction There's a parent , Then it inherits the sampling decision of its parent
• Absolute decision-making power is passed on to `startTransaction`

When more than one situation is possible , The following priority rules should be followed ：

1. If you pass the sampling decision to `startTransaction`（ See... Above Forcing a Sampling Decision）, Regardless of any other factor , Will use that decision .
2. If you define `tracesSampler` , Will use its decision . It can choose to keep or ignore any parent sampling decision , Or use sampling context data to make your own decisions , Or for transaction Choose a sampling rate .
3. If not defined `tracesSampler`, But there is a parent sampling decision , Then the parent sampling decision is used .
4. If not defined `tracesSampler` And there is no parent sampling decision , Will use `tracesSampleRate`.

Chinese documents are synchronized to ：

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official account ： Hacker afternoon tea .
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``````

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