Posts Tagged ‘cache’

HTML5 app cache

On my Nexus 7 today, I got this message from the FT app: FT could not be opened because it is not connected to the Internet. This is an odd error message.

The best way to fix this? Clear the cache in Android (just for the application). Or you can Force Stop the application afterwards and it should restart just fine.

Why? There are issues with HTML5 app cache. Some resources: Debugging HTML5 Offline Application Cache, Fixing app cache from the FT themselves, and some sensible comments at Stack Overflow.

How Facebook serves pictures

I caught Facebook – Needle in a Haystack: Efficient Storage of Billions of Photos on Flowgram. First up, I’m not a big fan of Flowgrams – the format is sensible, slide and voice, is excellent, but the delivery in a web browser isn’t optimal… make downloadable videos!

The talk however, was excellent. Do watch it, and learn a bit more about Facebook’s infrastructure. Anyway, some notes I took from the talk:

  • “We’re one of the largest MySQL installations in the world”
  • Use memcache – “We have memcache because databases aren’t fast” (later on in the questions)
  • Separate team focusing on APE (Apache, PHP and Extensions that they work on)
  • 6.5 billion total images, 4-5 sizes stored for each, so 30 billion files, of about 540TB total… During peak? 475,000 images served per second, and growing by 100 million uploads per week
  • Images are usually pulled from a Content Delivery Network (CDN), so it reduces the request rate on their servers
  • They use NetApp Storage, but basically their upload servers speak NFS to write to NetApp.
  • Cachr (evhttp based) and File Handle Cache use memcache as a backing store… FHC is based on lighttpd!
  • Makes use of a “haystack” – user-level abstraction, storing a separate index file that has more efficient metadata (to reduce disk seeks – 1 disk seek or less for any workload). Pretty deep in the discussion of the haystack server architecture, also evhttp-based
  • MySQL use? Very few transactions, very few joins
  • Video is a very different beast, and the design is a little different

If you’re into information about photo storage sites, don’t hesitate to also read my previous notes on Flickr.