Custom Instrumentation

Learn how to capture performance data on any action in your app.

To capture transactions and spans customized to your organization's needs, you must first set up tracing.

To add custom performance data to your application, you need to add custom instrumentation in the form of spans. Spans are a way to measure the time it takes for a specific action to occur. For example, you can create a span to measure the time it takes for a function to execute.

To get started, import the SDK.

Copied
import * as Sentry from "@sentry/remix";

There are three key functions for creating spans:

  • startSpan: Creates a new span that is active, and which is automatically ended. You'll likely want to use this function.
  • startSpanManual: Creates a new span that is active, which has to be ended manually.
  • startInactiveSpan: Creates a new span that is inactive, which has to be ended manually.

When a new span is started, it will automatically be started as a child of the currently active span, if there is one. This means that if a span is started as an active span, any spans that are created inside of the callback where the span is active will be children of that span. Additionally, errors will be tied to the currently active span, if there is one.

In contrast, inactive spans will never have children automatically associated with them. This is useful if you do not care about capturing child activity.

A key constraint for active spans is that they can only be made active inside of a callback. This constraint exists because otherwise it becomes impossible to associate spans with the correct parent span when working with asynchronous code.

In places where you are not able to wrap executing code in a callback (e.g. when working with hooks or similar) you have to work with inactive spans, and can combine this with withActiveSpan to manually associate child spans with the correct parent span.

In browser environments, spans are by default collected in a flat hierarchy where every span is the direct child of the root span. You can opt into a more fine-grained hierarchy but there are trade-offs.

The key reason for keeping a flat hierarchy is because in browsers it's impossible to reliably keep track of the active span across asynchronous boundaries. This means that if multiple asynchronous operations are started in parallel, it is not possible to determine which span is the parent of which child span. Imagine the following example:

Copied
Sentry.startSpan({ name: "span 1" }, async () => {
  await fetch("https://example.com/1");
  await fetch("https://example.com/2");
  await fetch("https://example.com/3");
});

Sentry.startSpan({ name: "span 2" }, async () => {
  await fetch("https://example.com/4");
  await fetch("https://example.com/5");
  await fetch("https://example.com/6");
});

In the browser, there would be no way to know that span 1 is only active inside of its callback, while span 2 is active in the other callback. Because of this, in reality, all fetch spans would become children of span 2. This is misleading and confusing, which is why by default in the browser, all spans will become children of the root span (which is usually the pageload or navigation span). This means that you will always have a flat hierarchy of spans.

This is a tradeoff that we have made to ensure that the data that is captured is accurate and reliable. If you need to capture a more complex hierarchy of spans, you can opt-out of this behavior by setting parentSpanIsAlwaysRootSpan: false:

Copied
Sentry.init({
  parentSpanIsAlwaysRootSpan: false,
});

This will revert to use the full hierarchy behavior, where spans are children of the currently active span. However, this may lead to incorrect data in the case of multiple parallel asynchronous operations - it is up to you to ensure there are no multiple parallel asynchronous operations that start spans in this case.

The following options can be used for all span starting functions:

OptionTypeDescription
namestringThe name of the span.
opstringThe operation of the span.
startTimenumberThe start time of the span.
attributesRecord<string, Primitive>Attributes to attach to the span.
parentSpanSpanIf set, make the span a child of the specified span. Otherwise, the span will be a child of the currently active span.
onlyIfParentbooleanIf true, ignore the span if there is no active parent span.
forceTransactionbooleanIf true, ensure this span shows up as transaction in the Sentry UI.

Only name is required, all other options are optional.

For most scenarios, we recommend to start active spans with Sentry.startSpan(). This will start a new span that is active in the provided callback, and will automatically end the span when the callback is done. The callback can be synchronous, or asynchronous (a promise). In the case of an asynchronous callback, the span will be ended when the promise is resolved or rejected. If the provided callback errors or rejects, the span will be marked as failed.

Start a span for a synchronuous operation:

Copied
const result = Sentry.startSpan({ name: "Important Function" }, () => {
  return expensiveFunction();
});

Start a span for an asynchronous operation:

Copied
const result = await Sentry.startSpan(
  { name: "Important Function" },
  async () => {
    const res = await doSomethingAsync();
    return updateRes(res);
  },
);

You can also nest spans:

Copied
const result = await Sentry.startSpan(
  {
    name: "Important Function",
  },
  async () => {
    const res = await Sentry.startSpan({ name: "Child Span" }, () => {
      return expensiveAsyncFunction();
    });

    return updateRes(res);
  },
);

Sometimes, you do not want the span to be ended automatically when the callback is done. In this case, you can use Sentry.startSpanManual(). This will start a new span that is active in the provided callback, but will not be automatically ended when the callback is done. You have to manually end the span by calling span.end().

Copied
// Start a span that tracks the duration of middleware
function middleware(_req, res, next) {
  return Sentry.startSpanManual({ name: "middleware" }, (span) => {
    res.once("finish", () => {
      span.setHttpStatus(res.status);
      // manually tell the span when to end
      span.end();
    });
    return next();
  });
}

To add spans that aren't active, you can create independent spans. This is useful when you have work that is grouped together under a single parent span, but is independent from the currently active span. However, in most cases you'll want to create and use the startSpan API from above.

Copied
const span1 = Sentry.startInactiveSpan({ name: "span1" });

someWork();

span1.end();

By default, any span that is started will be the child of the currently active span. If you want to have a different behavior, you can force spans to be the children of a specific span with the parentSpan option:

Copied
const parentSpan = Sentry.startInactiveSpan({ name: "Parent Span" });
const childSpan = Sentry.startInactiveSpan({ name: "Child Span", parentSpan });

childSpan.end();
parentSpan.end();

This option is also available for startSpan and startSpanManual.

We expose some helpful utilities that can help you with custom instrumentation.

Returns the currently active span.

Copied
const activeSpan = Sentry.getActiveSpan();

Returns the root span of a given span. If the span is already the root span, it will return the span itself.

Copied
const activeSpan = Sentry.getActiveSpan();
const rootSpan = activeSpan ? Sentry.getRootSpan(activeSpan) : undefined;

This method allows you to make a span active for the duration of a callback. You can use this in combination with startInactiveSpan to manually associate child spans with the correct parent span:

Copied
const span = Sentry.startInactiveSpan({ name: "Parent Span" });

Sentry.withActiveSpan(span, () => {
  // `span` is now active, any other spans will be children of it
  Sentry.startSpan({ name: "Child Span" }, () => {
    // Do something
  });
});

You can also pass null to withActiveSpan to ensure a span will not have any parent:

Copied
Sentry.withActiveSpan(null, () => {
  // This will not have a parent span, no matter what
  Sentry.startSpan({ name: "Parent Span" }, () => {
    // Do something
  });
});

Alternatively you can also use the parentSpan option to achieve the same:

Copied
const span = Sentry.startInactiveSpan({ name: "Parent Span" });
const childSpan = Sentry.startInactiveSpan({
  name: "Child Span",
  parentSpan: span,
});

Suppress the creation of sampled spans for the duration of the callback. This is useful when you want to prevent certain spans from being captured. For example, if you do not want to create spans for a given fetch request, you can do:

Copied
Sentry.suppressTracing(() => {
  fetch("https://example.com");
});

See Distributed Tracing for details on how to manually set up distributed tracing.

You can capture span attributes along with your spans. Span attributes can be of type string, number or boolean, as well as (non-mixed) arrays of these types. You can specify attributes when starting a span:

Copied
Sentry.startSpan(
  {
    attributes: {
      attr1: "value1",
      attr2: 42,
      attr3: true,
    },
  },
  () => {
    // Do something
  },
);

Or you can also add attributes to an existing span:

Copied
const span = Sentry.getActiveSpan();
if (span) {
  span.setAttribute("attr1", "value1");
  // Or set multiple attributes at once:
  span.setAttributes({
    attr2: 42,
    attr3: true,
  });
}

Spans can have an operation associated with them, which help activate Sentry identify additional context about the span. For example database related spans have the db span operation associated with them. The Sentry product offers additional controls, visualizations and filters for spans with known operations.

Sentry maintains a list of well known span operations and it is recommended that you use one of those operations if it is applicable to your span.

Copied
const result = Sentry.startSpan({ name: 'GET /users', op: 'http.client' }, () => {
  return fetchUsers();
})

You can update the name of a span at any time:

Copied
const span = Sentry.getActiveSpan();
if (span) {
  span.updateName("New Name");
}

Please note that in certain scenarios, the span name will be overwritten by the SDK. This is the case for spans with any of the following attribute combinations:

  • Spans with http.method or http.requrest.method attributes will automatically have their name set to the method + the URL path
  • Spans with db.system attributes will automatically have their name set to the system + the statement
Help improve this content
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").