Review again - you are incorrect. The op loads all of file 2 into memory (each time he reads a line from file 1!) but never loads all of file 1. He makes it look like he does by putting lines from file 1 in a hash, but that hash is local to the while block and thus never contains more than one line. Since file 2 is much smaller than file 1 I think it's quite reasonable to assume that while he might fit file 2 in memory+swap that's unlikely to work with file 1.

DB_File might work well enough, but it's hard to know. A lot depends on his definition of "fast enough" and the actual compositon of his data.

-sam