Manual:$wgDBtype

Details
Use:
 * "mysql" for MySQL
 * "postgres" for PostgreSQL (added in version 1.7)
 * "sqlite" for SQLite (added in version 1.13)

''Note that older versions may have used "pgsql" or "PostgreSQL" instead of "postgres". The documentation was updated to use 'postgres' in 1.8.0, but the switch may have been made earlier.''.