Squid use at Flickr

(Last updated Feburary 12 2007)

Flickr uses Squid as a reverse proxy accelerator in front of its photo storage service. All photos are stored on persistent, centralised storage which makes it easy to perform capacity planning - storage is added to handle more photos, Squid servers are added to serve increasing numbers of users and page views.

Flickr currently serves 30 million objects across its farm, with a hit rate of roughly 75-80%. Layer-7 URL hashing is used to send requests to the best cache to achieve such an optimal hit rate. They keep 3-5 hours of hot objects in each cache. Each Squid server handles approximately 1000 requests a second with the Squid-2.6 codebase.

Each cache is configured to use LRU as the memory and disk replacement policy and purposefully miss on objects above a certain size to optimise throughput and performance over higher cache hit rates.

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