Edge Cache

Edge Cache is currently in a public beta. Issues and feedback may be submitted to the Pressable.com support team.

Pressable provides Edge Cache across all plans, a free performance feature that allows your WordPress sites to leverage our global network of edge servers to deliver page and static asset cache.

Benefits of Edge Cache

Edge Cache provides performance improvements, especially in terms of your site’s Time to First Byte (TTFB), by serving page cache directly from the closest server available to a site’s visitors. This cache is served from Pressable’s four origin datacenters, and over 24 edge datacenters, giving sites a total of 28 Point of Presence (PoP) locations that are continuously expanding.

• Improved performance: Edge Cache can significantly improve the performance of your site by reducing the distance that requests have to travel. This can lead to faster page load times and improved TTFB, which can improve user experience, reduce bounce rates, and improve your site’s Core Web Vitals.
• Reduced resource utilization: Edge Cache can also reduce the load on your site’s origin server. Requests that are cached on our edge servers do not need to be fetched from your site’s origin server. This can help to improve the overall performance of your site and reduce resource utilization.
• Increased availability: Edge Cache can also increase the availability of your site via graceful failover. Requests can be served from the edge servers even if your site is experiencing an issue. This can help to ensure that your site is available to users, even while issues such as plugin and theme conflicts.
• Compatibility: Like Batcache, Edge Cache is compatible with dynamic requests that follow WordPress’ best practices, ensuring cached pages are not served when an uncached response is necessary. This includes compatibility with eCommerce solutions such as WooCommerce and ensures that checkout flows and cart requests are not cached.

One important point to note is that traffic that hits a site’s Edge Cache is not currently recorded in the standard web server logs.

Enabling and Disabling Edge Cache

To enable Edge Cache on your site, visit the MyPressable Control Panel and Settings for a specific site. From there, click on the Performance tab and locate the Edge Cache section.

Purging / Flushing Edge Cache

To purge, or flush, Edge Cache, visit the MyPressable Control Panel and access Settings for a specific site. From there, click on the Performance tab and locate the Edge Cache section.

Clicking the Purge Edge Cache will clear the current cache from our edge servers. Note that performance will be affected while cache rebuilds and it is recommended to use this tool sparingly.

How Edge Cache Works with Batcache Page Caching

Pressable leverages Batcache for general page caching. The Edge Cache respects the Batcache Time To Live (TTL) configuration. Therefore, extending the Batcache cache will result in the Edge Cache serving cached content for longer periods. However, it’s essential to note that each edge server operates independently. This means that different locations may have different caches.

Checking the Status of Edge Cache

After enabling Edge Cache, it can take time, and multiple site visits, for edge cache to built and be served.

You can monitor the status of Edge Cache by checking for the x-ac response header in your browser’s developer tools, via the shell command curl -LI https://your-example-domain/, and other methods.

Note that Batcache and Edge Cache will be disabled for your web browser’s session if you are currently logged into the backend, WP-Admin, of your site.

Here are some examples of these headers:

x-ac: 3.vie _atomic_dca HIT
x-ac: 2.den _atomic_dfw BYPASS
x-ac: 1.ewr _atomic_dca MISS

The value of the x-ac header can be HIT, EXPIRED, UPDATING, MISS, or BYPASS.

• HIT: The page was served from Edge Cache.
• EXPIRED: Response found in the cache but has passed the cache TTL. The response is returned then the item is removed from the cache.
• UPDATING: A request is currently updating the cached asset from the site’s origin server via a held lock to prevent multiple ‘misses’ for the same request.
• MISS: There was not an Edge Cache hit. This may be due to something disabling or preventing Batcache from working. Or, the page may not have had enough recent visits to populate the cache on the specific edge server the visitor connected to.
• BYPASS: Edge Cache is not enabled.

If the x-ac header’s value is HIT, EXPIRED, UPDATING, or MISS, this indicates that Edge Cache is enabled. If the header shows BYPASS, this means that Edge Cache is disabled.

Common Caching Issues

Configurations or issues that disable or break Batcache will also affect Edge Caching.

Note that Batcache and Edge Cache will be disabled for your web browser’s session if you are currently logged into the backend, WP-Admin, of your site.

The following are examples that will prevent optimal caching or may break caching altogether.

Cookies

Certain plugins may attempt to set cookies on each page load, especially those that leverage server-side cookies. This will prevent Batcache and Edge Cache from storing and serving cache.

• PHPSESSID server-side cookie AKA the “session cookie”, leverages PHP to store session IDs on the server side. Initiated via the session_start() function.
• Other set-cookie implementations that attempt to set a cookie on every request. Initiated via the setcookie() function.

Custom Cache Headers

Plugins and custom code may attempt to modify cache response headers. The following examples, when set, will prevent caching.

• pragma: no-cache
• cache-control: no-cache
• cache-control: max-age=0

Other Functions & Snippets

The following are additional examples of code that can prevent Batcache and Edge Cache from working as expected.

• batcache_cancel()
• $batcache->max_age = 0;
• $batcache['max_age'] = 0;
• session_start()
• nocache
• nocache_headers()
• x-cache
• wp_cache_flush()

Pressable API & Managing Sites in Bulk

The Edge Cache controls are also available via the Pressable API and can be used to enable, disable, and purge sites in bulk or via a custom control panel.

More on Caching at Pressable

For more information about caching and Pressable.com’s specific caching strategies, please refer to the following documentation:

• Modifying Cache Times with Batcache
• How Does Batcache Page Caching Work?
• Caching Types Available at Pressable

Frequently Asked Questions