Creating a single recid stream for multiple tables
You don't need a "reservoir", rather a way to generate a unique number.

Usually it is sufficient to give that task to one table you already have, and use AUTO_INCREMENT there, plus LAST_INSERT_ID().

But it you really need a sequence generator:


http://forums.mysql.com/read.php?10,616636,617041 (Simulating sequences)
http://dev.mysql.com/doc/refman/5.7/en/information-functions.html (search for "sequence")
http://forums.mysql.com/read.php?10,252807,262654 (A sequence solution)