JIRA uses a lot of images and hence a lot of image requests are made back to the server. This has a cost! A cost more than I think we realize.

One examination of JAC logs shows that 25% of request by count and time are for images. This is unexpected and worrying

Using CSS Sprites would be one way to alleviate some of this image serving load.

http://www.alistapart.com/articles/sprites

The FishEye team have used them with some sucess for 2.0 and we should too.

We have 173 icons in JIRA which are essentialy static. These could all be made into sprites.

One complication is that icons for issue types of configurable. However with an extra 2 fields we could make these sprite based as well.

For example issue type icons are currently forced in 16x16 image tags. W could tweak the issue type definitions to be

url :
x offset :
y offset"

And default then to be values for the 16x16 images. However for JIRA supplied issue type icons, they could come from a supplied sprite strip and have x/y offset values that are appropriate.

IF customs are image savvy then they can also use image sprite strips but if they are not then its still works for a single image!

This is a non trivial to perform since there are so many places images are used however I suggest we sneak up on it over time, get the 80-20 rule images in place first and then update others as JIRA evolves.

I think there are some good performance wins to be made here!