Comment 2 for bug 617536

1. for the purposes of formula files, their effectively immutable ( we store the hash as part of the storage key).

2. its a disk cache.. sizes is variable and not bounded. no lru needed as per 1.

general goal is to have a wrapper cache object around a provider file storage impl. given a request for a file key, check local storage, if it exists return openfile handle to it. if it doesn't fetch from provider storage, store in local, and return file handle to local.

hth