What causes 'Cache entry is expired' messages

[richardw...@gmail.com]

I've been looking at the PageSpeed Console and browsing the content of /mod_pagespeed_message and I'm getting lots of 'Cache entry is expired' messages.

The console is showing that historically about 40% of cache lookups were expired.

Apache isn't doing anything with Cache-Control headers (perhaps that's the problem).

How does PageSpeed decide that a cache entries should expire?

Thanks.

[Joshua Marantz]

It's based on the origin TTL of your resources.  If you have not specified any cache-control headers, then it defaults to 5 minutes.

Is that consistent with what you are seeing int he logs?

If you set your cache-control headers via something like:

<FilesMatch "\.(jpg|jpeg|gif|png|js|css)$">

  Header set Cache-control "max-age=3600"

</FilesMatch>

then the cache expiry would be one hour.

-Josh

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[richardw...@gmail.com]

I've added the cache-control header and the console is showing expired cache lookups have dropped from 40% to just above zero and the mod_pagespeed_message is looking a lot cleaner.

Thanks for the advice.