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Sampling (Volume Reduction)

SamplingMiddleware randomly drops a fraction of capture events to reduce analytics costs.

import { SamplingMiddleware } from '@drakkar.software/sunglasses-core';

// Keep only 10% of events (drop 90%)
const sampling = new SamplingMiddleware({ sampleRate: 0.1 });

// Consistent sampling: same user always included or excluded
const consistentSampling = new SamplingMiddleware({
  sampleRate: 0.2,
  consistentSampling: true,  // Based on anonymousId hash
});

// Sample only specific events
const targeted = new SamplingMiddleware({
  sampleRate: 0.05,
  onlyFor: ['page_view', 'hover'],  // High-volume events only
});

SunglassesCore.create({ middleware: [sampling], ... });

What is never sampled​

$screen, $identify, and $alias events are never sampled — only capture events are affected.

Kept events receive a $sample_rate property indicating the configured rate.