We have a large number of objects that we'd like to cache, running on mod_perl. We normally do this with MLDBM or some other file cache module that supports Perl multi-layer datastructures, but I'd like to explore an alternative using readonly scalars implemented via SvREADONLY, such as what Scalar::Readonly uses.

A big requirement is that the data stays shared between apache processes. Most of our applications don't need to write to the cache after server startup, so we can build the datastructures, set SvREADONLY flag on all its scalars, and should expect that the data stays shared.

We should be able to expect that our own code leaves the SvREADONLY flag alone to maintain sharing. However, I'm worried that perl will do something on its own that will end up with the scalars becoming unshared.

So my question is: how far can we rely on perl to keep SvREADONLY scalars shared?