Re: Seeing the same session_id used on different nodes alot in RAC 11g
- From: Riyaj Shamsudeen <riyaj.shamsudeen@xxxxxxxxx>
- To: dmarc-noreply@xxxxxxxxxxxxx
- Date: Fri, 27 Feb 2015 09:00:37 -0800
It's been a while, I researched this, things may have changed recently:
x$ksuse is the externalization of the session memory array (and a few other
x$ table were also externalizing that memory area starting with x$ksuse*).
There is also a freelist (a doubly linked list, I think) keeping track of
free slots in the array, protected by a latch. At the session logoff time,
that sid is added to the head of the linked list. At session logon time,
the element from the head of the list is assigned. That's the reason why
same sid is reused if you logoff and login quick succession.
Cheers
Riyaj Shamsudeen
Principal DBA,
Ora!nternals - http://www.orainternals.com - Specialists in Performance,
RAC and EBS
Blog: http://orainternals.wordpress.com/
Oracle ACE Director and OakTable member <http://www.oaktable.com/>
Co-author of the books: Expert Oracle Practices
<http://tinyurl.com/book-expert-oracle-practices/>, Pro Oracle SQL,
<http://tinyurl.com/ahpvms8> <http://tinyurl.com/ahpvms8>Expert RAC
Practices 12c. <http://tinyurl.com/expert-rac-12c> Expert PL/SQL practices
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<http://tinyurl.com/book-expert-plsql-practices>
On Fri, Feb 27, 2015 at 7:47 AM, Mladen Gogala <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
> On 02/27/2015 10:17 AM, Jeremy Schneider wrote:
>
>> This is a guess, but I think the session_id is just an offset into a
>> memory array of session info.
>>
>
> Yes, it is. And serial# is just the number of the times that the session
> slot has been reused.
>
> --
> Mladen Gogala
> Oracle DBA
> http://mgogala.freehostia.com
>
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