Thanks,
There a a few places where I needs this lookup and they vary a little.
Case1 : keys seem to be in 10 digit range and there are not many of them in use at the time, typically single digit number of keys. The objects are somewhat large, a couple of megabytes.
Case 2: keys are a little bit smaller, typically in the 4 digit range and there is normally a low double digit number of them. Objects are typically large, up to gigabytes but typically 10-100:ds of megabytes.
More background with what the whole thing is supposed to do is in here if you are in a reading mood 