Invalidating the cache

Posted by / 03-Apr-2015 10:16

Invalidating the cache

Since the content management system doesn’t necessarily hit a variant of the object that is cached, you have to issue acl purgers { "127.0.0.1"; "192.168.0.0"/24; } sub vcl_recv { if (req.request == "PURGE") { if (!~ purgers) { error 405 "Method not allowed"; } return (lookup); } } sub vcl_hit { if (req.request == "PURGE") { purge; error 200 "Purged"; } } sub vcl_miss { if (req.request == "PURGE") { purge; error 404 "Not in cache"; } } sub vcl_pass { if (req.request == "PURGE") { error 502 "PURGE on a passed object"; } } will keep getting the old content as long as this goes on.This is a known bug, and hopefully fixed by the time you read this warning.Banning in the context of Varnish refers to adding a ban to the ban-list.This is the entry that they were last checked against.Some questions you need to ask whenever the topic of cache invalidation comes up are: .This is typically done by letting your content management system send a special HTTP request to Varnish.Whenever you deal with a cache, you will eventually have to deal with the challenge of cache invalidation, or refreshing content.

The two use-cases for this is controlling who takes the penalty for waiting around for the updated content, and ensuring that content isn’t evicted until it’s safe. This means that you will have multiple copies of the content in cache.

The newest copy will always be used, but if you cache your content for a long period of time, the memory usage will gradually increase.

A ban statement might be “the url starts with /sport” or “the object has a Server-header matching lighttpd”.

Each object in the cache always points to an entry on the ban-list.

It can be done both through the command line interface, and through VCL, and the syntax is almost the same.

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