Oracle FAQ Your Portal to the Oracle Knowledge Grid

Home -> Community -> Mailing Lists -> Oracle-L -> Re: OPS on a single machine ?

Re: OPS on a single machine ?

From: Scott <>
Date: Tue, 04 Sep 2001 17:06:31 -0700
Message-ID: <>

Setfan, In OPS or RAC the locking is controlled by the DLM which is only communicated through the interconnect. The interconnect can be public or private. Private interconnects are highly recommended. Access to the data blocks by each instance is controlled by the DLM. DLM's communicate to each other via the interconnect. An instance cannot access a block without obtaining a PCM lock 1st(PCM locks are managed by the DLM). If the instance is doing a read the PCM lock is shared and all instances doing a read will also obtain a share lock. However if the instance is doing a DML then that instance will get an xclusive lock and that is the only instance that can access that block. If another instance requires that block then that instance has to request the holding instance to release the lock(Global enqueue). The holding instance writes the block back to disk the lock is released and the requesting instance now gets the PCM lock in a status (shared or xclusive) depending of the whether the activity is a select or DML. Now some of the disk I/O associated with DML changes in 9i because of cache fusion. You will also need the Cluster Manager that comes with your OS so Oracle can establish the communications between the nodes. Even if you want to install OPS an single node you still need the CM. Without the CM and OPS you cannot have 2 instances concurrently accessing the same disks. It doesn't matter whether the instances are on the same machine or not.


Do You Yahoo!?
Get email alerts & NEW webcam video instant messaging with Yahoo! Messenger
Please see the official ORACLE-L FAQ:
Author: Scott

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
To REMOVE yourself from this mailing list, send an E-Mail message
to: (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).
Received on Tue Sep 04 2001 - 19:06:31 CDT

Original text of this message