Re: Oracle 10 Failover

From: <>
Date: Thu, 11 Sep 2008 12:11:12 +0200
Message-ID: <>

On Thu, 11 Sep 2008 11:45:17 +0200, "Chris Seidel" <> wrote:

> wrote:
>> Dataguard can be configured in various protection modes.
>> One of them guarantees a commit on the primary will only execute if
>> the corresponding commit in the standby succeeds.
>> This means you should be able to guarantee zero-loss.
>Ah ok.
>> Using replication techniques you have no control over this, as Streams
>> etc replicate changes on table level, it doesn't work on transaction
>> level.
>So DG in synchronous mode is on tx-level.
>And DG on asychronous mode is much easier the handle (setup, monitor, etc)
>because it's on database level, not on table level.

Yes. Moreover both logical standby and Streams don't support all datatypes and suppress those tables automagically.

>>> OK, so you advice that one should use DG and not replication/streams
>>> to create a failover/standby server?
>> You need to answer whether you can afford data loss (or inconsistent
>> data) and how much down-time you can afford.
>> Apart from that you need to take into account Streams and other
>> options potentially require more manual intervention and are more
>> difficult to troubleshoot.
>Hm. For a standby database I now cannot see any why to use
>replication/streams instead of DG.
>Are there any reasons?

You should use (physical) standby if the standby should be 'bit-compatible' (ie identical), and plan to use it for no other purpose than DR.
If you only need part of the database in a secondary database, Streams might be the only way to go,
yet it will have impact on the application (you might need to set up primary keys and/or additional logging)
>> A completely different idea, and sorry I don't recall the product name
>> right now (it was an EMC product), is to replicate the disks, so
>> outside the database.
>Hm, it can replicate open redo logs?

That I don't know.

>> No, for me you have a distributed environment when you have two
>> *independent * databases which share data.
>> Let' s assume you have two different applications in two different
>> databases, both share 'reference data'
>> This can be accomplished by database links, it can be accomplished by
>> .. Streams etc. Actually *this* is the purpose of Streams.
>OK, understand.
>> A physical standby database isn't fully accessible, and doesn't
>> function without the primary. Even if they may be in two different
>> locations, they are not independent, so this is not a distributed
>> environment.
>OK. Makes sense ;)
>Thank you

Sybrand Bakker
Senior Oracle DBA
Received on Thu Sep 11 2008 - 05:11:12 CDT

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