Session replay is an add-on feature for paying customers only. You may try the feature for free for 14 days or 10,000 sessions (whichever comes first), after which you must contact Sales to continue use.
Session Replay will not slow your page-load time, and its unavailability will not impact your page. Some techniques we use to ensure high performance include:
- First loading a small initial “container” script (9kb, gzipped), from AWS’s CDN (content distribution network) typically in less than 30ms, followed by an asynchronously loaded SDK.
- The session replay script is optimized to minimize any blocking of the main UI thread and avoid user-visible “hangs”.
- Post-processing user events in an in-memory buffer to minimize work done before handing control back to the browser’s event loop.
- Throttling the rate of processing events (uploads of compressed data every 15s).
- Minimizing data sent over the wire by compressing DOM HTML (~30-40%) and not sending any externally fetched images, CSS, fonts, etc. (these are captured separately via the Heap Replay Bot).
- Caching crawled assets (session level, customer level) to minimize additional requests.
To further optimize performance, check if your site uses CSP directives, and if so, enable worker-src: blob (which improves UI performance by employing web workers).
For guidance that’s more general, see Will Heap slow down my site?