PostgreSQL Processes on a linux box

Hello,

altered a database using DBVisualizer. When I hit execute,
DBVisualizer stoped working and no I have two processes on my server:
postgres 30873 0.0 0.7 46552 7124 ? Ss 12:33 0:01
postgres: postgres dbName 10.0.1.198(53658) ALTER TABLE waiting
postgres 31007 0.0 0.6 46708 6500 ? Ss 13:07 0:00
postgres: postgres dbName 10.0.1.198(53799) SELECT waiting

What can I do? OK, I can stop and start the Database, but I think
there are other ways to handle this...
What Tool can I use to kill such processes?

Thanks and greetings,
Stefan Sturm