MariaDB (the new MySQL really free) is one of the management systems relational databases known in the world of free software (in fact, is used to indicate LAMP for Linux + Apache + MariaDB (MySQL) + PHP).
SQLite3 is another management system databases, but oriented embedded applications, used in applications like Firefox, Thunderbird, Android, i and to complete a long list of programs that use it.
The differences are basically that MariaDB (MySQL) is a server that services requests to be made to a port using a TCP/IP village while SQLite3 is more than a server, a library supported by most programming languages and providing access to a local file as a database is involved.
So as a summary we can say that SQLite3 is a database-oriented file while MariaDB (MySQL) is oriented as a service.
The problem I often have the database file is aimed at the crowd (check when you write another does not do to maintain the integrity of the file itself).
In SaltOS, is solved using POSIX semaphores that allow this type of control and thus avoid concurrent access 2 threads on the server, for example, at the same time to write.
SaltOS APIs define 2 functions calls semaphore_release and semaphore_acquire, which internally uses the PHP flock function that allows precisely the control of locking a file that is defined as a semaphore.
With this mechanism, it prevents competition on the SQLite3 database ensures the integrity of the file, and therefore the data.