Re: Scan Listener
- From: Sanjay Mishra <smishra_97@xxxxxxxxx>
- To: Guillermo Alan Bort <cicciuxdba@xxxxxxxxx>
- Date: Sun, 6 Oct 2013 16:22:48 -0700 (PDT)
Thanks Alan for your detailed explanation
Sanjay
________________________________
From: Guillermo Alan Bort <cicciuxdba@xxxxxxxxx>
To: Sanjay Mishra <smishra_97@xxxxxxxxx>
Cc: "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, October 4, 2013 10:59 PM
Subject: Re: Scan Listener
yes, you are correct. While SCAN Listener relocation is rather fast, you would
have a window of a few seconds while the listener on an active node starts up,
during which new connections using SCAN won't work. I highly recommend using at
least two SCAN listeners to avoid just that.
If you are working on a tiered environment and only an app server connects to
the database, then the issue becomes a bit more complicated, depending on
whether you have TAF or not, but as a rule if a database node goes down, then
the app server will likely issue new connections to the database to make up for
the lost ones (depending on how the app server is configured) and these new
connections would of course fail because they would happen just as the node
went down and while the SCAN listener is coming up on another node. Depending
on the app server this could cause some issues.
Client/Server probably apps won't be affected as much because end users would
have to actually attempt to connect in that tiny window. It is still possible,
depending on how the app is built, that as soon as the connection dies, the
user will attempt to reconnect, but in my experience with client/server apps,
they usually won't notice the dead connection until they try to "save" or get
some information, and only then the app will either error out, or attempt to
connect again (most likely it will error out and have the user connect again).
Then again, if you have the resources to have a RAC database, you probably have
most apps in an app server.
sorry if I digress a little.. it's been a while since I got to exercise the
"what if" part of my brain :P
Cheers
Alan.-
On Fri, Oct 4, 2013 at 10:58 PM, Sanjay Mishra <smishra_97@xxxxxxxxx> wrote:
Hi
>I want to check that if any RAC environment has used one DNS based Scan
>listener(DBA not provided correct requirement to the network and they assigned
>only one IP) and so RAC install has only configured one SCAN listener. Now if
>this is 4 Node RAC, and if the node containing SCAN listener goes down or
>crashed, it will take time to bring this scan listener on other surviving
>node. So want to check if during this time any app trying to connect using
>SCAN listener, then isn't this cause outage until SCAN listener is not up on
>second node. Also how long it will take to bring SCAN listener on surviving
>node. I know we can add more scan listener now but want to check the concept
>in the above scenario.
>
>TIA
>Sanjay
>
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