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What Is EPT?
Experienced Page Time (EPT) is a performance metric Salesforce uses in Lightning to measure page load time. EPT measures how long it takes for a page to load into a state that a user can meaningfully interact with.
A major difference between Salesforce Classic and Lightning Experience is that pages load progressively in Lightning, while pages in Classic are generated on request by the server. Because of the progressive loading from the client, any loaded component in the page can load more components at any time. Measuring when a page finishes loading in Lightning isn’t straightforward. Many factors can influence the EPT value.
Client-side and server-side factors both affect EPT. On the client side, the user’s browser, hardware, network quality, and their org’s complexity all affect EPT. On the server side, Apex and API processing and XMLHttpRequests (XHRs) impact EPT. For instance, component implementation details, errors, caching, and user interactions while the page is loading can all increase EPT.
Other things to consider:
- Lightning UI is rendered client side, making it sensitive to browser performance.
- Lightning UI requires many XHRs to render a page, making it sensitive to network latency.
- Complex pages with many custom fields and components slow page rendering.
The EPT is measured as the time from the page start to when no more activity occurs for at least two frames (~33 ms). The two extra frames help to avoid false positives due to asynchronous calls. These calls include any XHR activity, any storage activity, or any user interaction or client-side work of any kind in the main JavaScript thread.
