---
title: "Streamed Spans"
description: "Learn how the SDK sends spans in batches as they finish, and how to configure span attributes, filtering, and delivery."
url: https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans/
---

# Streamed Spans | Sentry for Flue

The Sentry JavaScript SDKs send spans in batches as they finish. This is called stream mode and is the default trace lifecycle. Service spans represent a service's entry point and group its child spans.

Why use stream mode?

* **No 1,000-span limit.** Spans are sent in batches, so a trace can contain more than 1,000 spans.
* **Lower memory usage.** Spans are flushed periodically and don't need to be held in memory until the root span ends. This is especially useful for long-running processes like queue consumers or cron jobs.
* **Faster visibility.** Span data arrives in Sentry as your application runs, instead of only after the entire operation completes.
* **No data loss from crashes.** If your process terminates unexpectedly, spans that were already flushed are preserved. Spans still buffered in memory can be lost.

You can find the following span types mentioned throughout this page:

* **Root span**: The topmost span in a trace. It has no parent span and is always a service span.
* **Service span**: A parent-level span at the entry of a service, identified by `is_segment` in its serialized data.
* **Child span**: Any span nested under a parent span within the same trace.

This graph shows how these span types relate to each other within a trace:

```bash
Trace
│
└── Root span [service A]
     ├── Child span
     │    └── Child span
     └── Service span [service B]
          ├── Child span
          └── Child span
```

## [Configuration](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#configuration)

[Configure tracing](https://docs.sentry.io/platforms/javascript/guides/flue/tracing.md#configure) in your app. The SDK uses `traceLifecycle: 'stream'` by default, with no additional integration required.

To opt out of span streaming, set [`traceLifecycle: 'static'`](https://docs.sentry.io/platforms/javascript/guides/flue/configuration/options.md#traceLifecycle). With this setting, wrap `beforeSendSpan` with `Sentry.withStaticSpan()` to receive and return `SpanJSON`. Transaction mode also supports [transaction filtering](https://docs.sentry.io/platforms/javascript/guides/flue/configuration/filtering.md#filtering-transaction-events) with `beforeSendTransaction` and `ignoreTransactions`.

How does span flushing work?

When stream mode is enabled, the SDK maintains an internal buffer that groups spans by trace ID.

Spans are flushed:

* On a regular interval (every 5 seconds by default).
* When a trace's buffer reaches 1,000 spans or the maximum size limit of a batch.
* When you call `Sentry.flush()` or `Sentry.close()`.

Each flush sends only the spans accumulated since the last flush, grouped into envelopes by trace ID.

## [Manual Instrumentation (Optional)](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#manual-instrumentation-optional)

Use the same span creation APIs in stream mode as in transaction mode. To measure operations the SDK does not instrument automatically, see [Instrumentation](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/instrumentation.md) for `startSpan`, `startSpanManual`, and `startInactiveSpan` examples.

## [Add Attributes](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#add-attributes)

To attach metadata to individual spans, see [Adding Span Attributes](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/instrumentation.md#adding-span-attributes).

### [Shared Attributes](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#shared-attributes)

Use [shared attributes](https://docs.sentry.io/platforms/javascript/guides/flue/enriching-events/attributes.md) to attach the same metadata to spans, logs, and metrics. Scope tags apply to errors and are not included in streamed spans.

## [Breadcrumbs](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#breadcrumbs)

Breadcrumbs are attached to errors. Streamed spans do not include breadcrumbs.

## [Extended Configuration (Optional)](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#extended-configuration-optional)

Modify span data before sending it or filter out spans you do not need.

### [Filter Spans](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#filter-spans)

Use [`beforeSendSpan`](https://docs.sentry.io/platforms/javascript/guides/flue/configuration/options.md#beforeSendSpan) to modify each finished span. In stream mode, the callback receives `StreamedSpanJSON` directly. Check `span.is_segment` to target only service spans.

The callback cannot return `null` to drop spans. See [Filtering Spans](https://docs.sentry.io/platforms/javascript/guides/flue/configuration/filtering.md#filtering-spans) for examples of modifying and dropping spans.

### [Drop Spans](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#drop-spans)

Use [`ignoreSpans`](https://docs.sentry.io/platforms/javascript/guides/flue/configuration/options.md#ignoreSpans) to drop spans by name, operation, or attributes. In stream mode, rules are evaluated when a span starts, so later name and attribute updates do not affect matching.

Ignoring a service span also drops its child spans. Ignoring a child span reparents its children to the nearest ancestor. See [Using `ignoreSpans`](https://docs.sentry.io/platforms/javascript/guides/flue/configuration/filtering.md#using-ignore-spans) for matching rules and examples.

## [Distributed Tracing (Optional)](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#distributed-tracing-optional)

Distributed tracing works out of the box when tracing is enabled and works the same way in stream mode. If you need to manually propagate trace context, for example, when the SDK can't instrument automatically, see [custom instrumentation for distributed tracing](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/distributed-tracing/custom-instrumentation.md).

## [Verify Your Setup](https://docs.sentry.io/platforms/javascript/guides/flue/tracing/streamed-spans.md#verify-your-setup)

Check the Traces view in Sentry for spans shortly after they finish. Enable `debug: true` to see SDK warnings, including callbacks that do not match the configured trace lifecycle.