File DBName.pid keeps dmserver running process id.

It's for using ‘dmserver –k’ to shutdown database, we need to know which process id is catched by dmserver, because we cannot get shared memory of 'dmserver -k' mode in shutdown, so keep this file for reference of 'dmserver -k' shutdown.

This file is useless if executing “terminate db” by dmSQL to shutdown database, it is ONLY for ‘dmserver –k’ mode.