Re: Doubts on Data Guard and Replication

From: DA Morgan <damorgan_at_x.washington.edu>
Date: Mon, 22 Nov 2004 21:41:07 -0800
Message-ID: <1101188378.919625@yasure>

Howard J. Rogers wrote:

> BlackBeltDBA wrote:
> [snip]
>

>> Switching to a standby database does incur *some* downtime. It's not an
>> automatic event. The application will probably fail and need to be
>> restarted once the standby comes back online. If you can not afford any
>> downtime you will probably want RAC.

>
>
> Could we perhaps kill this myth before it gets out of hand? There *is*
> downtime with RAC. Blocks that require re-mastering, as well as blocks
> which require instance recovery, will not be available until the
> remastering and the recovery have taken place. Your select will
> hang/pause/stall/whatever other word you'd like to use for an
> appreciable and measurable time until those things have happened. That
> means downtime in the sense of "Where's My Database Gone?!?"

Which we measure in fractions of a second. Looks like a network glitch not a "Where's my database gone"?

>> Alternatively, you can failover
>> to another peer in your replicated environment. However, there may be
>> some data loss that has to be handled. 

>
> There needn't be in Data Guard, but I think you covered that with the
> 'synchronous replication' stuff you mentioned earlier and which I snipped.
>

>> If a few minutes of downtime is
>> acceptable, a server cluster might be sufficient. If you can afford a
>> longer outage then a standby database should be sufficient.

>
>
> Don't disagree with that summary at all. I just don't like this "RAC is
> zero downtime" myth that is brewing in all quarters. It just ain't so.
>
> Regards
> HJR
BTW: TAF works with DataGuard too ... not just with RAC.

-- 
Daniel A. Morgan
University of Washington
damorgan_at_x.washington.edu
(replace 'x' with 'u' to respond)

Received on Mon Nov 22 2004 - 23:41:07 CST