Re: Seeing the same session_id used on different nodes alot in RAC 11g

From: <keydana_at_gmx.de>
Date: Fri, 27 Feb 2015 18:24:11 +0100
Message-Id: <E9F2CEEF-5B4B-42B9-91F8-611F6EB3BA28_at_gmx.de>

Wanted to know for a long time, this is the opportunity to ask, - what exactly do you mean by that (segmented array signifying „list is in-built“)?

Does it mean the structs (the elements of the array) have pointers to the previous & next element? (If yes, I wouldn’t have guessed that from the expression „segmented array“)

thanks!
Sigrid

> Am 27.02.2015 um 18:14 schrieb Riyaj Shamsudeen <riyaj.shamsudeen_at_gmail.com>:
>
> Minor correction: x$kuse is not just an array, it is a segmented array, which means that linked list is in-built.
>
> Cheers
>
> Riyaj Shamsudeen
> Principal DBA,
> Ora!nternals - http://www.orainternals.com <http://www.orainternals.com/> - Specialists in Performance, RAC and EBS
> Blog: http://orainternals.wordpress.com/ <http://orainternals.wordpress.com/>
> Oracle ACE Director and OakTable member <http://www.oaktable.com/>
> Co-author of the books: Expert Oracle Practices <http://tinyurl.com/book-expert-oracle-practices/>, Pro Oracle SQL,  <http://tinyurl.com/ahpvms8> <http://tinyurl.com/ahpvms8>Expert RAC Practices 12c. <http://tinyurl.com/expert-rac-12c> Expert PL/SQL practices <http://tinyurl.com/book-expert-plsql-practices>
>
> <http://tinyurl.com/book-expert-plsql-practices>
>
>
> On Fri, Feb 27, 2015 at 9:00 AM, Riyaj Shamsudeen <riyaj.shamsudeen_at_gmail.com <mailto:riyaj.shamsudeen_at_gmail.com>> wrote:
> It's been a while, I researched this, things may have changed recently: x$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 <http://www.orainternals.com/> - Specialists in Performance, RAC and EBS
> Blog: http://orainternals.wordpress.com/ <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 <http://tinyurl.com/book-expert-plsql-practices>
>
> <http://tinyurl.com/book-expert-plsql-practices>
>
>
> On Fri, Feb 27, 2015 at 7:47 AM, Mladen Gogala <dmarc-noreply_at_freelists.org <mailto:dmarc-noreply_at_freelists.org>> 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 <http://mgogala.freehostia.com/>
>
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Received on Fri Feb 27 2015 - 18:24:11 CET