MySQL provides a zero configuration DB library (libmysqld) which can create a standalone DB.
Can this standalone DB be merged into MySQL at a lightning speed?
SQLite DB can be merged into another at a blink of an eye, regardless of how much data it bears. All you have to do:
open database mydata.db;
attach database 'moredata.db' as attchdb;
insert into maindb.table select * from attchdb.table;