A couple of questions:

  1. What do the unique ids look like. How many of what characters?
  2. What do the account numbers look like. How many of what characters?

You say: "both the files contains the records of 37 million" and "The unique id can have more than one card account number"; both of which cannot be completely correct, because if both files contained the same number of records, there would have to be a one-to-one correspondance between unique ids and account numbers.

So which is it?

At what point do you run out of memory. Is it when building the hash of unique ids, or whilst populating the arrays with the corresponding account numbers?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re: Help on file comparison by BrowserUk
in thread Help on file comparison by Danu

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