Update: both of the files do *not* sorted, record_id is *not* unique in file-1, and file-2 is equally big (or bigger) and most likely going to change weekly.

Having said that, I really like the solution given by BrowserUk in the sense that my Benchmark gives a much faster result compares to my linear solution and I don't need to build any DB.

I haven't checked the memory usage with "vec()" though but I don't think I need to do that as BrowserUk has given an estimated comparison with a hash slurping :-)

Thanks.