Re: Online Upgrade
Date: Tue, 20 Mar 2012 08:17:15 +0100
Once I work at creating such environment that during possible downtimes applications used their cache entries until a database was available again :-), but this is not always possible. IMHO an application needs to be designed with possible db downtimes in mind
W dniu 20.03.2012 07:36, Purav Chovatia pisze:
> We have a requirement to apply application patches online i.e. without
> downtime. Our apps run in active-active mode and hence the app layer is
> taken care of i.e. while instance-1 of app is being upgraded, the live
> traffic is handled by instance-2. And once that is done, live traffic is
> handled by instance-2 and instance-1 is upgraded. However the challenge is
> to modify the DB objects i.e. SPs, tables, indices, etc.
> When I was given this requirement, initially I resisted. But later I
> thought, may be this looks like a common problem with increasing demand of
> high availability. So can you pls give me some guidance on how is this
> requirement handled across the industry? What do you all do?
> For e.g. if I have to modify a SP, I know that cannot be done while the
> apps are accessing it. Is there some workaround? May be writing wrappers,
> Similarly for other changes like adding or dropping a column.
> I think Edition based Redifinition is a step towards it but a first glance
> at it made me feel that its very complicated, still maturing, and does not
> cover all types of changes.
> If anybody has some best practices that are being followed can you please
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