> ## Knowledge Base Index
> Fetch the complete knowledge base index at: https://help.faaaster.io/sitemap.xml
> Use this file to discover available pages before exploring further.
> Pure-Markdown content can be obtained by appending a '.md' suffix to the content URLs listed in the sitemap (without the trailing slash).

# What are cache preloading and APCu for on Faaaster?

Both optimizations are set from the site's **Performance** tab. **Cache preloading** spares visitors from being the first to hit a page that isn't cached yet; the **APCu object cache** speeds up database queries.

## Cache preloading

According to the interface: "Prevents some visitors from experiencing slowdowns when a page has not yet been visited."

The server cache only fills up as visits come in: the first person to request a page waits for it to be generated. Preloading does this work ahead of time: when it is on, the site is crawled automatically on every startup to fill the cache. A manual cache purge does not restart this crawl.

## APCu object cache

According to the interface: "Improves loading performance by speeding up database queries."

## Setting them

1. Open the site, **Performance** tab.
2. In the **Cache** section, turn on **APCu object cache**. **Cache preloading** is on by default; its switch lets you turn it off.

These switches are reserved for the Owner, Admin and Member roles.

![The Cache section: preloading (1) and the APCu object cache (2).](https://storage.crisp.chat/users/helpdesk/website/-/9/d/2/d/9d2d3e0b7134b800/act-perf-cache-en_1lz53i6.png)

## Turning on APCu

APCu must be **installed in the environment** before it is active: after you turn it on, its status goes through an installation phase before it becomes operational. Allow a few moments, then refresh the screen.

If the option stays unavailable, your **server environment** is too old to support it. Update it from the **Server** tab, **Server environment** row, then come back.

## Which one should you turn on first?

**Preloading**, if your site is a showcase site or a blog: it removes the wait for the first visitor on each page.

**APCu**, if your site queries the database heavily — store, catalog, members area. It adds nothing to a site that is already served entirely from the page cache.

> **Turn them on one after the other**, and check the measurements in between: the **Performance** tab for response time, the **Monitoring** tab for resources. Two simultaneous changes will keep you from knowing which one produced the effect.

👉 [How do I monitor my site's performance?](https://help.faaaster.io/en-us/article/monitoring-12sd0a6/) · [Should I turn on the managed cron?](https://help.faaaster.io/en-us/article/managed-cron-12lv1jy/)