thumbnail-spec: proposing nested thumbnail cache directories

[Christian Neumair]

Dear xdg list,

Over at GNOME land we have the problem that due to the huge size of the
thumbnail directories, refreshing in-memory thumbnail readdir() caches
takes very long.

The caches are required as thumbnails are looked up for *every* file one
opens with the file manager, so the cumulative performance impact is
significant.

http://blogs.gnome.org/cneumair/2007/04/29/thumbnail-followup/
http://blogs.gnome.org/cneumair/2007/08/29/thumbnail-followup-2/

Alexander Larsson proposed to reduce this delay massively by using
nested directories - git does that as well:

The first two digits of the MD5 hash "4f831f...89" would be split apart,
and used to create a subdirectory "4f". The thumbnail file corresponding
to the specified example in this directory would then be named
"831f...89.png". So the entire hash maps to the file "4f/831f...98.png"
rather than "4f831f...98.png"

This definitly allows better cache-refreshing.

For backwards-compatibility, it may be a good idea to store this in a
new location, maybe ~/.thumbnails/hashed-failed and
~/.thumbnails/hashed-normal rather than ~/.thumbnails/normal and
~/.thumbnails/failed.

-- 
Christian Neumair <cneumair at gnome.org>