Re: About LATCH.session allocation

From: Taral Desai <taral.desai_at_gmail.com>
Date: Mon, 13 Jul 2009 14:15:43 -0500
Message-ID: <2b0cd5cd0907131215nafd4c29rdd86665c76224b93_at_mail.gmail.com>

Thanks Tanel for the information.
It too much asking but

For

#1 . Can you please elaborate or give example for this in which situation we will be waiting for new session to be created.

#2. Can you please explain more on "You can still ask latches with other (lower) levels in no-wait mode and I think there also some special cases involved."

On Sat, Jul 11, 2009 at 5:38 AM, Tanel Poder <tanel_at_poderc.com> wrote:

> 1. Session allocation latch is taken when a new session is about to be
> created by a process and we need to find & allocate a slot from session
> state object array (v$session). There's also a process allocation latch for
> allocating process state objects from v$process array.
>
> 2. Latch level is used for internal purposes, for detecting and avoiding
> possible latch deadlocks. Ideally this wouldn't be needed, but as there are
> bugs in software then the latch level assertion allows a problem latch get
> to fail with ORA-600 instead of causing a potential deadlock. When holding a
> latch with level X, you can only request with level greater than X in
> willing to wait mode. You can still ask latches with other (lower) levels in
> no-wait mode and I think there also some special cases involved...
>
> 3. One way to find out what block type IDs mean is this:
>
> SQL> select view_definition from v$fixed_view_definition where view_name =
> 'GV$WAITSTAT';
>
> VIEW_DEFINITION
> --------------------------------------------------
> select inst_id,decode(indx,1,'data block',2,'sort
> block',3,'save undo block', 4,'segment
> header',5,'save undo header',6,'free
> list',7,'extent map', 8,'1st level bmb',9,'2nd
> level bmb',10,'3rd level bmb', 11,'bitmap
> block',12,'bitmap index block',13,'file header
> block',14,'unused', 15,'system undo
> header',16,'system undo block', 17,'undo
> header',18,'undo block'), count,time from
> x$kcbwait where indx!=0
>
>
> --
> Tanel Poder
> http://blog.tanelpoder.com
>
>
> On Sat, Jul 11, 2009 at 7:14 AM, Taral Desai <taral.desai_at_gmail.com>wrote:
>
>> Hi All,
>> Can you please make me understand below things.
>>
>> 1. What is *LATCH*.*session allocation. We are seeing this in one of our
>> RAC environment for Jobs*
>> *2. What is v$latch.level. What is this used for.*
>> *3. Not regarding latch but how to get data block type list. I know
>> julian had mention on his site but how do we get this from database.
>> *
>> --
>>
>> Thanks & Regards,
>> Taral Desai
>> Shelley Winters<http://www.brainyquote.com/quotes/authors/s/shelley_winters.html> - "Whenever you want to marry someone, go have lunch with his ex-wife."
>>
>
>
>
> --
> Tanel Poder
> http://blog.tanelpoder.com
>
>

-- 

Thanks & Regards,
Taral Desai
Gilda Radner <http://www.brainyquote.com/quotes/authors/g/gilda_radner.html>
- "Adopted kids are such a pain - you have to teach them how to look
like
you."

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Received on Mon Jul 13 2009 - 14:15:43 CDT