Re: active_instance_count behavior
- From: Andrey Kriushin <Andrey.Kriushin@xxxxxxxx>
- To: orclwzrd@xxxxxxxxx
- Date: Wed, 15 Nov 2006 01:36:40 +0300
Hi,
AFAIK, the only two components which know about INSTANCE_ROLE are the
instance itself and the listener. The later is informed about this fact
by corresponding PMON process.
In any other respect the instance with INSTANCE_ROLE=STANDBY_INSTANCE is
no worse than that with PRIMARY_INSTANCE role. You can run jobs on the
standby instance, you may fill library/row cache with the objects from
primary instance (DBMS_LIBCACHE). You event can allow ordinary users to
connect and work with standby instance.
The listener will show the status of the service as BLOCKED, thus
preventing connections to it. However you have 3 ways to walkaround:
1. Local connections (no listener involved) will be successfull
2. Use static configuration in listener.ora, use
(CONNECT_DATA=(SID=...)) in tnsnames.ora (i.e. <=8.0 syntax)
3. Use (CONNECT_DATA=(SERVICE=..)(INSTANCE_ROLE=ANY)) in tnsnames.ora
Thus why any static remastering should occur (dynamic one doesn't work
in 9i anyway). On the other hand, in 10gR2 there are chances that
dynamic remastering will change the mastering responsibility in more
reasonable way.
BTW, are you really ready to pay 50% more for licenses with a kind of
50% less processors in use just in order to save few minutes max (say,
for creating SGA) on instance restart? I mean, you not planning to use
second instance at all? I think, that designers of this "solution" just
made it quick & dirty with a thought similar to "why not do it, if it is
so easy?" and "marketroids will be happy". ;-)
HTH
-- Andrey
John D Parker wrote:
Ok, in a 2 node RAC 9.2.0.5(yes, I know, don't ask). We have an
active/passive configuration with active_instance_count=1 set in both
instances. This makes instance prd1 the primary. My question hinges
around behavior of block mastering and cache coherency. In normal
active/active RAC, each node "masters" approx half the datablocks.
Does this behavior change when I have a primary node? I would think i
would. However, I can't find any docs one way or the other. With a
Primary node and blocks being mastered like in active/active, the
primary node would be continually asking the passive node for blocks
which seems very inefficient. It would make more sense for the primary
node to master all the blocks and behave much like a pre 8.1.7 OPS
node. Any thoughts here? I'd really like to see some docs one way or
the other but I can't seem to locate any.
--
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