The query was computing the count for all mailing lists, not just the
one being requested. This prevents optimizing the SELECT with indexes.
In addition, using a subselect for the blacklist forced a full table
scan on the contacts - switching to a LEFT JOIN avoids that.
With a blacklist of a few hundred thousand entries, and a table of
mailing list contacts in the same order of magnitude, this brings the
SELECT from 3+ seconds down to 3 milliseconds - with the same result.
Bonus: no need to perform the regexp extraction of emails to test for
NULL values -> substring(x) is NULL iff x is NULL.
Olivier Dony
8545e05fc0