yumdb: utility of from_repo_revision and from_repo_timestamp

Hi,

OLPC has a custom OS update system based on rsync of differences of 1
filesystem image to the next.

To make this as quick and efficient as possible, we have an interest
in reducing needless delta between the old version and the 2.

Currently, every time we do a new build, there are huge differences in
the yumdb, even if the set of installed packages didn't really change
between the 2  builds. This is because the from_repo_revision and
from_repo_timestamp files change under each db entry.

We'd save time if we could avoid changes in those files.

So, my question is: what is the utility of those files? I see that
they get displayed with the "yumdb info" command. Anything else?
If I were to set the value 0 in all of those
from_repo_revision/from_repo_timestamp files, meaning that they
wouldn't change from build-to-build, would there be any obvious side
effects?

Thanks,
Daniel