Andrew Green wrote: > In particular, I'm > looking for reassurance that passing a reference to a hash doesn't copy > the hash itself into memory in any way, and that the memory overhead is > only as large as the largest $item.
That's basically correct, but some dbm implementations will use their own caching and that may increase this overhead. > Similarly, if I was to > > use vars(%hash); > > and initialise the tied hash as a global, does this have a significant > memory overhead? No, it's the same except for the addition of an entry in the symbol table. > Does untie-ing the hash clear the hash contents from > memory, or do I also need to undef the hash to avoid the hash contents > persisting from one request to the next? If you actually want to free the memory, you need to undef it. The untie prevents it from persisting, but the memory stays allocated unless you undef. > Is one approach better than the > other? Not in terms of memory. The thing you need to think about with regard to dbm files is how to make sure they are synchronized between multiple processes. You basically just need to untie them after each request (unless it's read-only data). By the way, MLDBM::Sync takes care of all of that for you. - Perrin
