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Re: TAF

From: Tim Gorman <Tim_at_SageLogix.com>
Date: Fri, 07 Jun 2002 05:18:27 -0800
Message-ID: <F001.004775EC.20020607051827@fatcity.com>


Fawzia,

PRECONNECT establishes the second/failover database connection along with the first/primary, so your client-server database connection is really client-server1/server2. Should the first/primary connection fail, then you failover to the second.

BASIC establishes only the first/primary database connection but has the information available to establish the second/failover connection should the first/primary fail.

PRECONNECT will failover faster, as the second/failover connection has already been established. In a large environment (i.e. hundreds of database connections) full of BASIC connections, you can expect the mass exodus from one database instance to the failover to cause BASIC connections to wait a noticeable amount of time.

One problem with PRECONNECT that I've noticed is the scenario where the second/failover instance is terminated for some reason first. Let's say a bunch of PRECONNECT TAF connections are working away happily via their first/primary connection to the primary database instance, and there is some reason to terminate the second database instance or some/all of the second/failover database connections to the second database instance. In this case, PRECONNECT will not notice the loss of the second/failover database connection, allowing the first/primary connection to continue working happily away. But after bringing the second database instance back online, if the first database instance should now fail, then all those PRECONNECT sessions will simply fail.

Upshot: BASIC is more "robust", because it fails over only when it needs to, but you can get caught in a "traffic jam" in the event of failover. PRECONNECT can fail over faster because of previously established failover connections, but if anything happens to that second connection after the time it is established, then you'll be out of luck.

Hope this helps...

-Tim

>
> Hi ,
>
> I am configuring TAF on oracle 8.1.7 (solaris). I was just wondering if
> anyone on the list has had experience on this and can give me any advice-
> more specifically on the the method- preconnect and basic. Are there any
> significant benefits of having the preconnect setting set?
>
> Any input would be really appreciated..
>
> Rgds
>
> Fawzia
>
>
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> Author: Malik, Fawzia
> INET: Fawzia.Malik_at_bskyb.com
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Tim Gorman
  INET: Tim_at_SageLogix.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
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Received on Fri Jun 07 2002 - 08:18:27 CDT

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