void mongoc_database_set_write_concern (mongoc_database_t *database, const mongoc_write_concern_t *write_concern);
This function sets the write concern to use on operations performed with database. Collections created with mongoc_database_get_collection() after this call will inherit this write concern.
The default write concern is MONGOC_WRITE_CONCERN_W_DEFAULT: the driver blocks awaiting basic acknowledgment of write operations from MongoDB. This is the correct write concern for the great majority of applications.