Framework RSL’s in Flex Builder vs Flash Builder, Performance and Important Info | Devgirls Weblog

If you are running multiple Flex applications on a server you should seriously consider using Flex Framework RSLs (runtime shared libraries) to reduce redundancy by eliminating the loading of the same core framework libraries used by all applications. The result could be a reduction in the size of your application SWF file to 1/10th of the original size! I recently implemented this approach for Tour de Flex since each of our hosted samples is its own application and would ultimately contain a large amount of code shared by all the other samples. I saw the size of the swf’s for the samples go from 572k to 57k just by making one small change, removing the core Flex Framework RSL’s from the resulting swf.

The good news is, in Flex 4 previously optimized core framework RSL’s are enabled by default and dynamically linked at runtime (versus compiled into the code via the ‘merged into code’ option). This option is specified in the project properties under Flex Build Path. Under the Library Path tab there you will see a Framework linkage selection that should look like the screenshot below and use runtime shared libraries by default. If it does not show that as the default, you can also select Runtime Shared Libraries from the drop-down list to ensure they are used.