RE: DataGuard
- From: "Laimutis Nedzinskas" <Laimutis.Nedzinskas@xxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 19 Jan 2007 14:35:19 -0000
From: Boris Dali [mailto:boris_dali@xxxxxxxx]
>Please see some comments in line...
>1. At least in our case observer communicates to the primary using the
same network path as the users.
Observer doesn't reach primary, users don't reach primary. It's that
simple.
I suspected that :-) Anyway, this must be part of observer setup
requirements. Is it? Well, it is for me at least.
However there is still a possibility that primary "wakes up". What do
clients prevent from connecting to it?
>I believe the target standby needs to know that all transactions
committed on primary have been applied on this standby. Up to the last
committed SCN. And yes this information is readily available at the
standby.
I already described the scenario of primary crashing while standby is
unavailable (in other words - primary crashing in downgraded performance
mode.) Standby is unaware then of primary's progress. It's quite a
simple protocol issue. The same situation arises in distributed
transactions. Oracle has the term "pending transactions" and requires
manual resolution.
P.S.
Please note that I am not considering likelihood of such situations. I
am not considering the fact that overall system HA is much more than
database HA. A simple application bug may diminish all HA and data
protection provided by the database. Anyway I am trying to get as much
as possible from the DG.
Fyrirvari/Disclaimer
http://www.landsbanki.is/disclaimer
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