Manual:$wgDBtype

Details
Type of database. added in version 1.5 ) added in version 1.7 ) added in version 1.13 )
 * "mssql" - MS-SQL
 * "mysql" -
 * "oracle" - (
 * "postgres" - (
 * "sqlite" - (

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.