hopehope_123

Hi Gurus,

I was an Informix man , but my last job needs Oracle skills which i
have no experience. My question is about oracle real application
clusters. I know that
oracle's shared everything architecture uses Dlm (distributed lock
manager ) and for large installations this was a problem. But all the
oracle white papers say this was history. Their cache fusion tech.
solved all the problems.
Is there any one who can comment on this?

Kind Regards,
hope

a blonde

Hi Gurus,

I was an Informix man , but my last job needs Oracle skills which i
have no experience. My question is about oracle real application
clusters. I know that
oracle's shared everything architecture uses Dlm (distributed lock
manager ) and for large installations this was a problem. But all the
oracle white papers say this was history. Their cache fusion tech.
solved all the problems.
Is there any one who can comment on this?


Hi ho, hi ho, it's off to troll we go...

Have you tried an Oracle group dude?

AB

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sending to informix-list

mark townsend

Sure - here to help :-)

The DLM was never really that big a problem, although people liked to
think it was. The real issue was as follows

Setup
-----
Block A on disk
Block A loaded into memory on Node 1
Block A loaded into memory on Node 2
Change to Block A in memory on Node 1
Change or Read of Block A in Memory on Node 2 requires a synchronization

Previous Behaviour
------------------
1) Node 1 would write changed block to disk
2) Node 2 would read changed block from disk for the query
This was known as a 'ping', and IO could quickly become a bottle neck if
you didn't design your app to reduce the number of cross node 'pings' of
data. And after the re-design, you would need to then partition your
data to make the design work

Now, with Cache Fusion
----------------------
1) Node 1 pokes the changed block from it's memory to Node 2's memory
No IO, no need to re-design app, partition data etc

alexey sonkin

Cache fusion definitely solves 'disk deadlock' problem
for OLTP systems, not DSS. For DSS, I think that XPS is
still much better.
XPS is not suitable at all for OLTP.

------------------------------------------
Alexey Sonkin
Senior Database Administrator


sending to informix-list

alexey sonkin

P.S.
Sorry for using 'deadlock' instead of 'bottleneck' in previous email

Cache fusion definitely solves 'disk bottleneck' problem
for OLTP systems, not DSS. For DSS, I think that XPS is
still much better.
XPS is not suitable at all for OLTP.


------------------------------------------
Alexey Sonkin
Senior Database Administrator

sending to informix-list

francisco roldan

Great explanation!

Since which Oracle version was changed the behaviour ?

regards

-----Mensaje original-----
De: Mark Townsend [mailto:markbtownsend@attbi.com]
Enviado el: Jueves, 31 de Julio de 2003 09:31 a.m.
Para: informix-list@iiug.org
Asunto: Re: oracle cache fusion against informix XPS?


Sure - here to help :-)

The DLM was never really that big a problem, although people liked to
think it was. The real issue was as follows

Setup
-----
Block A on disk
Block A loaded into memory on Node 1
Block A loaded into memory on Node 2
Change to Block A in memory on Node 1
Change or Read of Block A in Memory on Node 2 requires a synchronization

Previous Behaviour
------------------
1) Node 1 would write changed block to disk
2) Node 2 would read changed block from disk for the query
This was known as a 'ping', and IO could quickly become a bottle neck if
you didn't design your app to reduce the number of cross node 'pings' of
data. And after the re-design, you would need to then partition your
data to make the design work

Now, with Cache Fusion
----------------------
1) Node 1 pokes the changed block from it's memory to Node 2's memory
No IO, no need to re-design app, partition data etc
sending to informix-list

mark townsend

Well - I'm sort of in the business slightly. (I work for Oracle)

Complicated question. You need to ask yourself when a synced block would
be required in Node 2.

Obviously, if Node 1 had written to the block in memory, and Node 2 also
needed to write to the same block, then a sync of the two memory images
would be required - and Oracle9i introduced the "memory to memory sync
operation" for this situation.

However, Oracle also requires a synced block on a read operation. Oracle
will construct before images of data so that writers don't block readers
- called multi version read consistency (or snapshot isolation, as
Microsoft is starting to call it).

So even a read of the block on Node 2 could require that the information
in memory on Node 1 (the current memory image of the block, and the
information needed to rollback that image), be flushed back to disk for
use on Node 2 (known as a consistent read in Oracle parlance). Oracle8i
introduced the "memory to memory sync operation" for this situation.

hopehope_123

Thank you very much for your great explanation Mark.

Kind Regards,
hope