posthog-performance-tuning

name	posthog-performance-tuning
description	Optimize PostHog performance: local flag evaluation, client batching config, event sampling, efficient HogQL queries, and serverless flush patterns. Trigger: "posthog performance", "optimize posthog", "posthog latency", "posthog caching", "posthog slow", "posthog batch", "posthog fast".
allowed-tools	Read, Write, Edit
version	1.12.0
license	MIT
author	Jeremy Longshore <[e-mail]>
tags	["saas","posthog","api","performance"]
compatibility	Designed for Claude Code

PostHog Performance Tuning

Overview

Optimize PostHog for production workloads. The biggest performance wins are: local feature flag evaluation (eliminates network calls), proper batching configuration, event sampling for high-volume apps, and efficient HogQL queries with date filters.

Prerequisites

• posthog-node and/or posthog-js installed
• Personal API key (phx_...) for local flag evaluation
• Feature flags configured (if applicable)

Instructions

Step 1: Enable Local Feature Flag Evaluation

The single biggest performance improvement. Without local evaluation, every getFeatureFlag() call makes a network request (~50-200ms). With local evaluation, flag definitions are cached and evaluation is instant (~0.1ms).

import { PostHog } from 'posthog-node';

const posthog = new PostHog(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
  host: 'https://us.i.posthog.com',
  // This is the key: personal API key enables local flag evaluation
  personalApiKey: process.env.POSTHOG_PERSONAL_API_KEY,
  // Flag definitions are polled every 30 seconds by default
  // Adjust if you need faster flag updates:
  // featureFlagsPollingInterval: 10000, // 10 seconds
});

// With personalApiKey set, this evaluates locally (no network call)
const variant = await posthog.getFeatureFlag('pricing-experiment', 'user-123', {
  personProperties: { plan: 'pro', country: 'US' },
});

// Get all flags at once (still local, still fast)
 allFlags =  posthog.(, {
  : { :  },
  : { : { :  } },
});