Well, the greatest novelty in RAC is synchronizing blocks without write to
disk. Here is it how it works:
OPS:
1. Instance A requests instance B to downgrade its (PCM) lock for block C
from X --> N.
2) Instance B writes block C to disk and downgrades lock to N.
3) Instance A reads block C into its own SGA and upgrades lock from N --> X
RAC:
1) Instance A requests instance B to downgrade its (PCM) lock for block C
from X --> N.
2) Instance B sends the current version of block C through the interconnect
to the instance A and downgrades the lock from X --> N.
3) Instance A puts the received block into its own SGA and upgrades the lock
from N --> X.
Also, RAC can deliver a read consistent version of a block, but OPS in 8.1.7
can do that too (BSP process). This was sold as "cache fusion". With the
advent of ultrafast interconnects such as HP hyperfabric (4GB/sec), it became
much faster to develop a mechanism for sending a block down the pipe instead
of writing it to disk and reading it from disk. Also, with the ultrafast CPUs
with the usual usage not surpassing 10%, it became acceptable to use
releasable locks which require a great deal of string copying and hash
searching, both fairly CPU intensive operations. Hashed (static) locks,
covering a fixed range of blocks, were much cheaper in CPU terms but the false
pinging was just killing the OPS, especially after new files have been added..
RAC is much, much faster. Nevertheless, I'd advise functional partitioning of
the application system on both RAC and OPS so that related data is accessed
from the same node, thus minimizing DML overhead. Oh yeah, I forgot, it's no
longer just "DML", it "IDML" now ("I" stands for "Integrated").
On 2003.06.22 23:34, "Kaing, Leng" wrote:
Hi,
I don't remember seeing any doco as such, but you need to look at what's new
in RAC and compare it to OPS. eg. No pinging on read and write, easier admin.
etc. Can't remember off the top of my head.
Rgs,
Leng.
----------
From: "VIVEK_SHARMA" <[EMAIL PROTECTED]>
Date: Wed, 18 Jun 2003 11:16:31 +0530
Subject: RAC vs. OPS a comparison ?
RAC vs. OPS any comparison study , doc , link ?
Need it for customer already on OPS , who is considering moving to RAC
Thanks
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