Manual:$wgDBtype/en

Details
Type of database.
 * "mssql" - MS-SQL
 * "mysql" - (Will default to the newer MySQLi driver if enabled on the server.  Otherwise, falls back to the legacy MySQL driver.)
 * "oracle" - (added in version 1.5)
 * "postgres" - (added in version 1.7)
 * "sqlite" - (added in version 1.13)

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.