An external database is out of the question.

and

Speed is of utmost importance.

You make them sound mutually exclusive when in fact, you have an oxymoron. If you want real speed, then you want a real database. Perhaps if you explain why it is "out of the question", we can give you more appropriate guidance. Using a Any_DBFile may meet your criteria but no one claims that it screams speed. Why not use the database solution?

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