Well despite my asking you still don't really supply useful detail. Probably Out Of Memory error at 950MB with 14GB free RAM is appropriate given you say you have a lot of memory.

Now this is total speculation but you call it an intermediate step. This makes me think you are either doing a merge or a filter based on the content of the hash. Either case can be dealt with by using a merge sort strategy. If the data in your hash is stored in a sorted flat file (sorted by hash key) and the data it is to be merged with/filtered against is similarly sorted then you can very efficiently make a single pass theough both files in lockstep, generating a final output file. The basic algorithm is to open both files, and read a line from each. If the keys are the same do a merge and output, if not read another line from the file where the key < other_file_key. Thus you rapidly walk both files and find all mathcing keys.