[spotman]

Curious, is the:

  SELECT DISTINCT(email) FROM parent;

The actual query you run in production, or similar enough? That could be a very expensive query with a very large amount of rows, even if indexed. (Large, being in the multi millions, depending on hardware). Might make more sense to run something like that on a reporting slave.

[Sinjo]

That was a fabricated example, rather than something plucked from our codebase. It's the sort of query we avoid running on our production database.

I agree with your approach though. Our data analysis runs elsewhere.