Re: [Q] How does Oracle 9i-RAC handle lock to suport HA?

First of all, thanks for your answer.
I'm sorry for my poor English.
What I really want to know is how to recover the lock information managed by failed node - such as who has the recent version of block or who has the exclusive/shared mode lock about this table/row among several instance - when instance failure is detected. I.e., how is the content of GCS and GES enqueue recovered.

> Now, it's not really that simple, because the GCS CAN'T be on one node

> only - single point of failure which is what we want to get away from for

> HA. The GCS is actually duplicated on each node that is running an Oracle

> instance.

 Does "The GCS is actually duplicated on each node that is running an Oracle instance" means following?

• the GCS and GES enqueue information about resources(data) mastered by one instance is duplicated on more than two node.
• when instance failure is detected, GCS and GES enqueue is reconstructed using duplicated information

Thanks for your reading.

Hun Soon LEE

"Pete Sharman" <peter.sharman_at_oracle.com> wrote in message news:NHi%7.3$MX6.24_at_inet-nntp1.oracle.com...
> I'm not 100% clear on what you're asking for here, but here's a summary I
> sent to someone recently:
>
> In the RAC environment, the DLM you refer to is called the global cache
> service. It keeps track of the instances that are locking blocks. Let's
take
> a simple example of a 3 node cluster with instances 1 and 2 (located on
> nodes 1 and 2) interested in a block, and the global cache service located
> on node 3. Instance 1 wants to take out an exclusive lock on a block which
> has an SCN of 1000. First thing it does is ask the GCS who has that block.
> If no-one is using it, the GCS tells instance 1 that, and instance 1 then
> reads the block from disk and communicates the fact that it has taken out
an
> exclusive lock to the GCS. GCS records the fact that instance 1 has the
> block in exclusive mode, local mode (i.e. in one cache only) with no past
> images (more on this anon) - status is XL0 for instance 1 (X = exclusive,
L
> = local, 0 = no past image)
>
> Instance 1 now makes a change and commits it (SCN is now 1001). Again it
> communicates this to the GCS, which updates the SCN information it's
> tracking. Status is still XL0.
>
> Instance 2 now decides it wants to update another row or even the same row
> in the same block (Instance 1 has committed so another update to the same
> row is fine). Instance 2 asks the GCS who has the block. GCS tells
instance
> 2 that instance 1 has it, and tells instance 1 to send it to instance 2
> ACROSS THE INTERCONNECT (i.e. no pinging to disk which is where the
> performance hit came in OPS). Instance 1 either gets it from the data
buffer
> cache if it's still there or from its rollback (or undo) segments, sends
the
> block across the interconnect and then tells the GCS it has it. GCS
changes
> the status for instance 1 to NG1 (N = null - no lock, G = global because
the
> block is now in two caches, 1 = past image - this is no longer the most
> recent copy of the block). Instance 2 receives the block, tells the GCS it
> has it, so the GCS now changes the status for instance 2 to XG0 (exclusive
> lock, global mode, 0 means this is the current image). Instance 2 can now
> change the block and do whatever it wants.
>
> Now, it's not really that simple, because the GCS CAN'T be on one node
> only - single point of failure which is what we want to get away from for
> HA. The GCS is actually duplicated on each node that is running an Oracle
> instance. That way, each node can tell very quickly where the latest copy
of
> a block is, and can request it from the instance holding that latest copy.
> Of course explaining it with the GCS on each node gets way complex with
> arrows pointing every which way when you do it on a whiteboard, so that's
> why I stick to the simple example when explaining it.
>
>
> --
> HTH. Additions and corrections welcome.
>
> Pete
> Author of "Oracle8i: Architecture and Administration Exam Cram"
>
> "Controlling developers is like herding cats."
> Kevin Loney, Oracle DBA Handbook
>
> "Oh no, it's not. It's much harder than that!"
> Bruce Pihlamae, long-term Oracle DBA
>
> "Hun Soon Lee" <hunsoon_at_etri.re.kr> wrote in message
> news:a1k267$hdu$1_at_news.kreonet.re.kr...
> > Hello there.
> > I want to know how Oracle9i-RAC handles the lock to suport HA.
> > According to the "Oracle9i-RAC concepts",
> > it uses DLM(Distribute Lock Manager) to manage the lock.
> > I want to know details about how Oracle 9i-RAC handles the lock.
> > Does it backup the lock manager to support HA?
> > Does it use the lock caching to increase performance?
> > etc...
> > Thanks for your reading.
> > Hun Soon LEE
> >
> >
>
>
Received on Fri Jan 11 2002 - 04:46:54 CST