4. do something special if $dbh->do is called in non-void context.

If called in void context, keep the current iterator way. If called in a non-void context, fetch all the records in memory and return number of records fetched.

Document that calling $dbh->do in non-void context will load all records in memory.

This should keep the old behaviour (which was loading all records already) and provide a new, compatible way of fetching records that uses less memory.

Liz

Update
Another idea: recreate the query using COUNT() instead of the selected fields if $dbh->do is called in non-void context. Return the result of that query as the number of records. This would allow you to keep the current memory friendly behavior even when the number of records is requested. The risk of course is that the number of records is incorrect because of database updates between the SELECT COUNT() and the original SELECT.