Re: Semaphores and Oracle on Unix

semaphore is the low level mechanism for process synchronization and protection of critical areas in the process's address space (such as oracle server process). for the purpose of protection of critical areas, semaphores are used to identify the ownership of critical data or memory structurs. they are passed around by the O/S in a certain way. the process that happens to have the semaphore is allowed to modify a certain segment, while others have to wait for their turns.

latches and locks are Oracle concepts. it's likely that they are implemented using semaphores to protect memory sturcturs and physical objects such as rows and tables.

In article <EHtqww.AH.0.debian_at_sirena.rinet.ru> Konstantin Kivi <konst_at_sirena.rinet.ru> writes:
>arpege <arpege_at_imaginet.fr> wrote:
>> I've read that each Oracle process needs a semaphore to be available to
>> access the SGA. Is that right and if so why ?
>> What is alto the difference between latch's and semaphores ?
 

>> Best Regards
 

>> Philippe (arpege_at_imaginet.fr)
>
>I am not sure what do you mean under latch, but semaphore is
>a unix (posix) way to order access from different process
>to different objects on the system (SGA in our case).
>man ipc
>man semget
>man semop
>man semctl
>
>Konstantin
Received on Sat Oct 11 1997 - 00:00:00 CDT