latches or semaphores

Hello,

According to my tests, Oracle doesn't use semaphores on latch operations. It's also true in theory since semaphore operations are done in FIFO order, but latches not. Semaphores include atomic test-and-set instructions too. But, using just atomic test-and-set instructions for latches are enough instead of using expensive entire semaphore operations.

what happens if hardwares don't support atomic test-and-set instructions ?

If Oracle doesn't use, how is the latch positing implemented ? Which IPC mechanism is used ? There are two options other than semaphores:

• message queues
• shared memory

message queues are not solution, becasue they are ordered. I guess posting is done shared memory IPC mechanism.

I would like to be sure about this case to confirm my knowledge. does Oracle use semaphore on latches ?

thanks in advance... Received on Tue Nov 13 2001 - 08:13:03 CST