Author:

Per Buer is the CTO and founder of Varnish Software, the company behind the open source project Varnish Cache. Buer is a former programmer turned sysadmin, then manager turned entrepreneur. Runs, cross country skis and tries to keep his two boys from tearing down the house.

Twitter: Follow Per Buer on Twitter

Cache Invalidation Strategies With Varnish Cache

Phil Karlton once said, "There are only two hard things in Computer Science: cache invalidation and naming things." This article is about the harder of these two: cache invalidation. It’s directed at readers who already work with Varnish Cache. To learn more about it, you’ll find background information in “Speed Up Your Mobile Website With Varnish.”

varnish-cache

10 microseconds (or 250 milliseconds): That’s the difference between delivering a cache hit and delivering a cache miss. How often you get the latter will depend on the efficiency of the cache — this is known as the “hit rate.” A cache miss depends on two factors: the volume of traffic and the average time to live (TTL), which is a number indicating how long the cache is allowed to keep an object. As system administrators and developers, we can’t do much about the traffic, but we can influence the TTL.

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