There are code paths in the getColumn method that needs an implementation, this should be doable.
The PgSql specific PDO functions (pgsqlLOBCreate and friends) needs to be implemented. However, at least for now this is not possible with the way the PDO implementation is done inside HHVM. Some changes needs to happen in ext_pdo and possibly pdo_driver as well.
This is a two fold issue:
getColumn
method that needs an implementation, this should be doable.ext_pdo
and possiblypdo_driver
as well.