Oracle on Windows

Oracle and Microsoft are considered to be bitter rivals. Both are leading the software market of the world so the rivalry is understandable. But as the matter of fact both are forced to consolidate each other by their business needs. Just the hint of it, is the growing intentions of Oracle to support more and more .Net platform and Microsoft is doing vice versa as well. In this post I am not going to discuss their business policies about each other rather I will try to explain the specific Oracle architecture on Windows. Although Oracle is platform independent and most of the management tools of it run similar on every platform but of course there are differences as well. It is so because every operating system has its own way of handling resources and applications. Furthermore process and memory management are different as well.

Unlike Linux which is process based, Windows is thread based. In Windows process is not the work horse rather it is just a container to hold threads. Threads are created by the process that contains those threads. It then uses those threads for the real work. So when Oracle gets started a process initiates and then it creates the threads for the real work. So the different background processes that Oracle uses like PMON, SMON, DBWR etc are treated as threads by Windows. So you will not be able to see these processes in Task Manager, the same thing is possible in Linux. In Task Manager you will only see one process and mainly it will be named as Oracle.exe. This process will create individual threads for the working.

What this means for the DBA is to understand that when you start Oracle Database service from MMC then it does not mean that Oracle Database gets started. Although it is necessary to start the service but this does not guarantee the startup of Oracle Database. Normally when the Oracle service is on automatic start then it does both the tasks. But when you had to manually start then first you start the Oracle service and then issue startup command from SQL*PLUS while logging as sys. The first will create the Oracle process and startup command will start your instance (Oracle Background processes (individual threads on Windows) and Shared Global Area).