1.What is the difference between stopping the services of a database and shutting it down through svrmgrl.
2.What if some one shutdown the database server without stopping the services or shutting down the database through svrmgrl.
I presume that you are running oracle in Windows NT. Im not really sure with this, but you need the services to automate the startup and shutdown of your database. During startup, Windows NT runs these services, with this you dont need to startup of database manually in server manager the same goes when you shutdown the server, it stops the services thus shutting down your database.
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when you shutdown or startup the service the process invokes the file oracle.exe along with the corresponding database to start the database or shutdown the database just like what you do with the startup and shutdown command thru svrmgrl.
No problem somebody can surely shutdown the database server the service will automatically shutdown the database
Someone correct me if I'm wrong.... But, I've always been of the understanding that you want to shutdown the DB through svrmgrl before shutting down the services. By shutting down the services only, the DB does not shutdown cleanly. Only by shutting down through svrmgrl with a valid shutdown command (shutdown immediate, etc) will the DB shutdown cleanly.
The service is just NT's mechanism for allocating the memory space in the OS for the Oracle.exe to run in. NT runs all threads in the same service (UNIX runs each process in a separate OS process)
You can shut down the instance with a 'shutdown' in svrmgrl, which leaves the service running. I personally prefer to do this if I want to get a clean shutdown, UNLESS you have the services set up right. There is a way to create another service that runs a script and starts/stops the instance and the service. (so you'd have two services per instance, one to start/stop and another to run Oracle) If it's 8.1.5 or better, it should handle this for you, and I *believe* 2000 only needs the one service. (not sure on this)
If you're getting crash recovery messages in your alert log, then your service is NOT handling the clean shutdown of the instance--the OS is pulling the rug out from under the Oracle process. So it's doing an instance recovery every time it comes back up. It only matters if it is not for personal use and you're taking cold backups or care about those log messages.