What is Vary Cache?

Vary Cache is a new feature in FastPixel which will store different cached versions of the same page depending on the value of one or more cookies you choose.

Normally, a page cache works like this:

• User A visits /about
• The page is generated and cached
• User B visits /about
• User B gets the same cached page

With cookie-based variation:

• User A has cookie membership=gold
• User B has cookie membership=silver
• The cache stores separate versions of /about for each cookie value
• Each user receives the correct cached content

Please note that Vary Cache will not work if you do not set one or more important cookies!

Why it’s needed #

Some websites show different content based on cookies, such as:

• Logged-in vs logged-out users
• Membership levels
• Geographic preferences
• Language selectors
• A/B testing variants
• WooCommerce cart/session states
• Location based currency or tax

Without varying by cookie, users could see the wrong content because everyone would receive the same cached page.

Trade-offs #

Pros

• Allows caching personalized content.
• Improves performance compared to disabling cache entirely.

Cons

• Can dramatically increase cache size if cookie values are highly variable.
• May reduce cache hit rates because fewer visitors share the same cached page.

Important caution #

Avoid varying by cookies that contain unique values per visitor, such as:

session_id=abc123

session_id=xyz789

This effectively creates a separate cache for every user, defeating most of the performance benefits of page caching.

A good rule is: only vary by cookies that have a small number of possible values and actually affect what is rendered on the page.