Re: BAST in RAC
- From: Mladen Gogala <mgogala@xxxxxxxxxxxxxxxxxxxx>
- To: Amir.Hameed@xxxxxxxxx
- Date: Thu, 23 Dec 2004 11:00:11 -0500
Hameed, Amir wrote:
>I am trying to clear my concept on what BAST (blocking asynchronous
>system trap) is and how it works in RAC. I have not been able to find
>much information on Metalink. I would appreciate if someone can explain
>it.
>Thanks
>Amir
>
>
I see that you've been reading Steve's books. AST or Asynchronous System
Trap is
a VMS (= Very Mighty System) concept which does not have a direct
equivalent in
Linux/Unix world. The closest thing to AST in Linux world are signals.
To get better
acquainted with signals and their implementation, you should read any
Unix internals
books, like the ones from Maurice Bach, Uresh Vahalia, M.K. McCusick or
R. Heinlein.
Blocking AST elevated IPL (Interrupt Priority Level) above 2, so no
other AST's
could be delivered while the non-blocking AST was executing. Signal
handlers normally
don't do that. Blocking AST's are implemented either as user-mode
threads (see pthreads
"caterpillar" book) or by using some other synchornization mechanism
like a specialized
device (a.k.a "post-wait" device) semaphores or latches. Blockikn AST
(BAST) works
on RAC systems only with the ARD extension.
--
Mladen Gogala
Oracle DBA
Ext. 121
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