Cache Notes

ToDo List

Here are some things we can investigate to gain more information about the current state of the cache:

• Determine what the cache's average hit rate is.
• See how performance varies by increasing the cache size.
• Look into whether YouTube files are blowing out the cache.
• Run a Test Pilot or a smaller experiment to gather user cache data
  • In order to gather info on the previous bullet points

Here are some ideas for improving the cache that need to be investigated:

• Consider other eviction options
  • Prioritize by file type, giving css and js higher priority
  • Evict based on "frecency", not just recency (frequency + recency)
  • Use Adaptive Replacement Cache algorithm: http://en.wikipedia.org/wiki/Adaptive_replacement_cache
  • We could consider letting servers specify "cache-priority" with resources. This leads to other issues, like fairness.

• Keep dimensions of evicted image files, so layout can still render before the image data arrives across the network
• Compress cache entries?
  • This could save space and improve I/O time
• Don't throw away the entire cache when the browser crashes.

And here are some miscellaneous items:

• Add more info to about:cache, including hit rates and other info.

List of Other Cache Resources

Here are some links with other documentation on the cache.

• hacks.mozilla article on revitalizing caching
• http://www.mozilla.org/projects/netlib/presentations/necko1-2002-02-18/slide11.xml
• https://developer.mozilla.org/en/HTTP_Caching_FAQ
• My notes on the HTTP cache protocol.

Here is a list of bugs filed on the cache. Many are resolved.

• (http_cache) Meta-bug: improve HTTP cache bug 559729
• Eliminate synchronous reads from cache (make cache reads asynchronous): bug 513008
• Remove sync writes from current cache: bug 513074
• Write/flush cache metadata off main-thread: bug 549767
• xpcshell tests: assertion "mem cache leaking entries" in nsMemoryCacheDevice::Shutdown() causing abort test failed: bug 548406
• Replace necko cache with the Google Chrome cache: bug 514213
• Implement modern cache: bug 512849
• Disk Cache overflow when downloading large files: bug 443067
• Cache corruption when viewing sites with several large images (simultaneous hash collision & cache dooming by disk cache size limit): bug 321361
• Increase default disk cache size: bug 193911
• Figure out the max nr of entries we should store in the disk cache: bug 569709
• Some files are never cached due to hash collisions which are quite common due to weak string hash function: bug 290032
• Firefox stores corrupted version of cached JavaScript file (merges two files together): bug 355567
• Need to teach necko to deal with channels reading and writing to a cache entry simultaniously: bug 446876