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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Oracle Internals
HP, it is sleep/wake/check. it is up to the process to acquire the resource. AFAIK, there is no message-passing type of algorithm to tell waiting (whether spinning or sleeping) processes when the semaphore becomes unset ( ie the resource is available ) Sleeps are expensive in Latchville, and you can track their occurence via v$latch_waits and the SLEEP* columns.
hope this partial answer helps.
-----Original Message-----
From: Henry Poras [mailto:Henry.Poras_at_ctp.com]
Sent: Tuesday, March 13, 2001 10:25 PM
To: Multiple recipients of list ORACLE-L
Subject: Oracle Internals
I have been rereading Steve Adam's book a bit more carefully and have a question. Just wondering if anyone has any answers.
When talking about latch sleeps, the book states "a process sleeping for a latch waits on its semaphore". However, latches don't support queuing and a number of processes may be waiting for the same latch. If I am sleeping and the latch frees, who knows I need that semaphore? Are all waiting processes posted with the semaphores going on/off/on/off? or is no semaphore posted and the processes go sleep/wake/check/sleep/wake/check? I can't quite picture the details here.
Henry
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