$ADODB_COUNTRECS

If the database driver API does not support counting the number of records returned in a SELECT statement, the function RecordCount() is emulated when the global variable $ADODB_COUNTRECS is set to true, which is the default. We emulate this by buffering the records, which can take up large amounts of memory for big recordsets. Set this variable to false for the best performance. This variable is checked every time a query is executed, so you can selectively choose which recordsets to count.