About the st-* files.

Dear Jigsaw authors,
I am now studying Jigsaw's source code trying to understand how it works,
but one thing confused me a lot is 
what the stores are? 
what does the files in the /config/stores do? 
When I do some benchmark(some stress test) agaist jigsaw,
echo time Jigsaw will creat almost a thousand st-* files in that directory,
what do these files present? The cache? And what kind of cache?
Does Jigsaw have any file-content caching when it is running?
Thanks a lot.
Regards,
Robin