On Sun, Oct 10, 2010 at 8:56 AM, Graham Leggett <minf...@sharp.fm> wrote: > Hi all, > > One of the things that needs to be fixed with mod_cache is the support for > caching varying responses. In the current cache, we store it as below, as an > additional directory tree below the original URL's directory tree. This > wastes lots of inodes, and is very expensive to write. > > /tmp/cacheroot/ > /tmp/cacheroot//1uq > /tmp/cacheroot//1uq/w...@d > /tmp/cacheroot//1uq/w...@d/Fok > /tmp/cacheroot//1uq/w...@d/Fok/HRU > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62 > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header.vary > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header.vary/thJ > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header.vary/thJ/bK5 > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header.vary/thJ/bK5/im1 > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header.vary/thJ/bK5/im1/RSz > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header.vary/thJ/bK5/im1/RSz/fCK > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header.vary/thJ/bK5/im1/RSz/fCK/YHquMmA.data > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header.vary/thJ/bK5/im1/RSz/fCK/YHquMmA.header > > What I have in mind is to move the varied content into the main tree, like > this: > > /tmp/cacheroot/ > /tmp/cacheroot//1uq > /tmp/cacheroot//1uq/w...@d > /tmp/cacheroot//1uq/w...@d/Fok > /tmp/cacheroot//1uq/w...@d/Fok/HRU > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62 > /tmp/cacheroot//1uq/w...@d/Fok/HRU/I62/QSJf2JA.header > /tmp/cacheroot//thJ > /tmp/cacheroot//thJ/bK5 > /tmp/cacheroot//thJ/bK5/im1 > /tmp/cacheroot//thJ/bK5/im1/RSz > /tmp/cacheroot//thJ/bK5/im1/RSz/fCK > /tmp/cacheroot//thJ/bK5/im1/RSz/fCK/YHquMmA.data > /tmp/cacheroot//thJ/bK5/im1/RSz/fCK/YHquMmA.header > > We reuse the same directory structure in the process, and keep the original > QSJf2JA.header file indicating that the URL is a varied URL.
The problem with the second layout is that it makes it near impossible to clear out all variants of a URL easily. I think there are far more general issues with waste of inodes on the cache disk format, than anything to do with varres. I would rather change the defaults to use only two letters and two levels deep for the cache directories, and probally restrict the character set even further to just [a-zA-Z]. I think a case should be made for not using sub-directories inside the .varies folder. Instead just flatten it out and put all the variants inside a flat directory, rather than distributing them over the cache again. Thanks, Paul
