Re: The same session run on both instances (RAC), is it normal?

  • From: Dan Norris <dannorris@xxxxxxxxxxxxx>
  • To: exriscer@xxxxxxxxx, staywithpin@xxxxxxxxx
  • Date: Thu, 27 Sep 2007 05:37:44 -0700 (PDT)

I'm with LSC--all you know is that the same session ID is connected to the 
database multiple times, not necessarily through a different instance. Many 
applications (including SQL*Plus) will open multiple database sessions for 
certain operations and that's the expected behavior. I believe that those 
additional sessions (at least in the case of SQL*Plus) are made using the same 
database connection, so they should land on the same instance. 

In addition to gv$session.inst_id, you might also need to check out the columns 
gv$session.failover_type and failover_method to see if those "extra" sessions 
are the result of a preconnect session.


----- Original Message ----
From: LS Cheng <exriscer@xxxxxxxxx>
To: staywithpin@xxxxxxxxx
Cc: oracle-l <oracle-l@xxxxxxxxxxxxx>
Sent: Thursday, September 27, 2007 1:23:55 AM
Subject: Re: The same session run on both instances (RAC), is it normal?

how about group by inst_id...?



On 9/27/07, qihua wu <staywithpin@xxxxxxxxx
> wrote:We have a two nodes RAC, the strange thing is that many sessions run on 
> both nodes.

      select sid from gv$session group by sid having count(*)>1
they are lots of rows return.

My understanding for load balance is:  if sessions on instance 1 are too many, 
then new session will be connected to instance 2.

But if at the beginning there were100 sessions on both inst1 and inst2, after 
all the sessions on inst2 are completed, no existing session on instance1 will 
go to instance2. 

But the fact of the above query told me some sessions run on both instance. How 
can this be true?

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