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Optimize Sentry's performance monitoring pipeline to maximize signal quality while minimizing SDK overhead and event volume costs. Covers the v8 SDK API for @sentry/node, @sentry/browser, and sentry-sdk (Python), targeting sentry.io or self-hosted Sentry 24.1+.
Sentry.init() called with a valid DSN before any application code runs
Performance monitoring enabled (tracesSampleRate > 0 or a tracesSampler function)
Access to the Sentry Performance dashboard to verify changes
Instructions
Step 1 — Replace Static tracesSampleRate with Dynamic tracesSampler
A flat tracesSampleRate: 0.1 samples all routes equally. The tracesSampler callback makes per-transaction decisions based on route, operation type, and upstream trace context.
// Higher sampling for write operations (mutations are riskier)
if
startsWith
'POST '
startsWith
'PUT '
return
0.25
// Moderate sampling for read APIs
if
startsWith
'GET /api/'
return
0.1
// Low sampling for background work
if
startsWith
'job:'
startsWith
'queue:'
return
0.05
// User-tier sampling (via custom attributes from middleware)
if
'user.plan'
'enterprise'
return
0.5
return
0.05
// Default: 5%
Step 2 — Configure Profiling with profilesSampleRate
The profilesSampleRate controls what fraction of traced transactions get profiled. Setting it to 1.0 with a 5% tracesSampler means 5% of traffic is profiled.
Tuning: Start at profilesSampleRate: 0.1 in production. Profiling adds ~3-5% CPU overhead per profiled transaction. Continuous profiling (profileSessionSampleRate) has lower per-transaction cost but runs on sampled instances continuously.
Names with dynamic IDs (/api/users/12345) create thousands of unique entries, degrading dashboard performance and inflating quota. Route templates go in the name, dynamic values go in attributes.
// BAD — creates thousands of unique transaction entries// GET /api/users/12345, GET /api/users/67890, ...// GOOD — Sentry auto-parameterizes Express/Koa/Fastify routes// GET /api/users/:userId// For custom spans, always parameterize:Sentry.startSpan(
{
name: 'order.process', // No dynamic IDs in nameop: 'task',
attributes: {
'order.id': orderId, // Filterable in Discover queries'order.total_cents': totalCents,
'customer.tier': customerTier,
},
},
async (span) => {
const result = awaitprocessOrder(orderId);
span.setAttribute('order.status', result.status);
return result;
}
);
Detect cardinality issues with a Discover query:
SELECT count(), transaction FROM transactions GROUP BY transaction ORDER BY count() DESC
Step 4 — Add Custom Measurements
Custom measurements appear in the Performance dashboard and can be charted, alerted on, and queried in Discover. Unit types: 'millisecond', 'byte', 'none' (count), 'percent'.
-- Slowest transactions (p95)
SELECT transaction, p95(transaction.duration), count()
FROM transactions WHERE transaction.duration:>1000
ORDER BY p95(transaction.duration) DESC
-- Regression detection (20%+ slower vs last week)
SELECT transaction, p75(transaction.duration),
compare(p75(transaction.duration), -7d) as vs_last_week
FROM transactions GROUP BY transaction
HAVING compare(p75(transaction.duration), -7d) > 1.2
-- Span breakdown for a route
SELECT span.op, span.description, p75(span.duration), count()
FROM spans WHERE transaction:/api/checkout
ORDER BY p75(span.duration) DESC
Output
Dynamic sampling active — health checks at 0%, payments at 100%, defaults at 5%
Profiling enabled with profilesSampleRate or continuous profileSessionSampleRate
Transaction names parameterized — cardinality under 500 unique names
Custom measurements tracking business KPIs alongside latency
