Re: Semaphores and Oracle on Unix

arpege 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)Latches are internal to the database. Semaphores are are logical names
within the operating system. They are used to access shared resources.  They are usually allocated 1 per process. A unix warning or error will occur if more processes than semephores exist. This can be alleviated by either increase the number of semephores, or lowering the processes in the init.ora file.

Latches are somewhat simular, however are within the Oracle database processes. They are most often associated with redo logs. A latch is required in order to recieve the instruction to write out to a redo log.  If the request goes out and there is not a latch available, then a timeout occurs. You can see this in the v$latch table.

Hope this helps.

-Sheilah Scheurich
DBA
to respond via email remove the underscores Received on Mon Sep 29 1997 - 00:00:00 CDT