Your question is really ´How can I know a process is running and get information about it?´. For this question a database is a poor solution. A still poorer solution is a PID-File. The best solution would be a FIFO, aka named pipe. Because every process closes its filedescriptors at the end of its run (even if SIGKILLED) and a FIFO behaves different if its open by another process, you can surely detect if a process is running. Steps to take:

Exclusively gain access to the FIFO(done with another FIFO)

Stat FIFO: if empty no process

Open FIFO

Read FIFO

Write back to FIFO

Close FIFO

Give up exclusive access

The Server does only:

Exclusively gain access to the FIFO(done with another FIFO)

Open FIFO

Write PID to FIFO

Not close FIFO

Give up exclusive access