Invalidating a cache no credentials cache file found while validating credentials
Each object in the cache always points to an entry on the ban-list.
This is the entry that they were last checked against.
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.
This is a known bug, and hopefully fixed by the time you read this warning.
A ban is one or more statements in VCL-like syntax that will be tested against objects in the cache when they are looked up in the cache hash.
A ban statement might be “the url starts with /sport” or “the object has a Server-header matching lighttpd”.
A second con is that the ban list can get fairly large if there are objects in the cache that are rarely, if ever, accessed.
To remedy this, Varnish tries to remove duplicate bans by marking them as “gone” (indicated by a G on the ban list).
Sometimes, however, you need that extra performance you can get when explicitly invalidating.
Whenever you deal with a cache, you will eventually have to deal with the challenge of cache invalidation, or refreshing content.