Performance & tracing

Tracing answers "why was that request slow?" — which database call, which HTTP hop, which LLM call ate the time.

Setup

Turn on trace sampling in the SDK. Everything else (framework middleware, DB drivers, HTTP clients) is instrumented automatically by the official SDKs.

sentry_sdk.init(
    dsn="…",
    traces_sample_rate=0.2,        # 20% of requests
    environment="production",
    release="myapp@1.4.2",
)

Sentry.init({
  dsn: "…",
  integrations: [Sentry.browserTracingIntegration()],
  tracesSampleRate: 0.2,
  tracePropagationTargets: ["localhost", /^https:\/\/api\.example\.com/],
});

Sampling strategy

• Development: 1.0.
• Production: start at 0.1–0.2. Traces are billed per span (Tracing service), and a busy service produces a lot of them.
• Need precision on one endpoint? Use a traces_sampler function that returns 1.0 for the routes you care about and a low rate for health checks.

Distributed tracing

To follow one request across services, the SDK propagates sentry-trace and baggage headers. Set trace_propagation_targets (backend) / tracePropagationTargets (browser) to include your own API hosts, and make sure your reverse proxy does not strip those headers.

Custom spans

with sentry_sdk.start_transaction(op="task", name="nightly-settlement") as tx:
    with tx.start_child(op="db.query", description="SELECT … FROM ledger"):
        rows = fetch_rows()
    with tx.start_child(op="http.client", description="POST /gateway/verify"):
        verify(rows)

In the UI

Performance lists transactions for the selected project with:

• Throughput (events per period) and latency (avg, p50…p99)
• Failure rate
• Filters by environment, release, operation, time period and user — pick a person and the routes and jobs narrow to the ones they triggered (the same filter as on issues and logs; the Users page links straight into it)

Open a transaction to get the trace waterfall: every span with its duration, nesting and tags, so you can see the serial database calls or the slow third-party hop directly.

Spans tagged gen_ai.* or mcp.* are additionally projected into AI monitoring.

Dashboards

The transactions dataset is available to dashboards with count(), avg(duration), sum(duration), failure_rate() and p50–p99 percentiles, grouped by transaction, op, status, environment, release or platform.

Troubleshooting

Symptom	Cause / fix
No transactions at all	traces_sample_rate is unset or 0
Traces stop at the service boundary	Propagation targets don't include the callee, or a proxy strips sentry-trace/baggage
Browser transactions but no backend spans	The backend SDK isn't initialized, or its sample rate is much lower — a child inherits the parent's sampling decision only when the headers arrive
Costs climbing	Lower traces_sample_rate, or sample health-check routes to 0 with traces_sampler