Call now: 252-767-6166  
Oracle Training Oracle Support Development Oracle Apps

 E-mail Us
 Oracle Articles
New Oracle Articles

 Oracle Training
 Oracle Tips

 Oracle Forum
 Class Catalog

 Remote DBA
 Oracle Tuning
 Emergency 911
 RAC Support
 Apps Support
 Oracle Support

 SQL Tuning

 Oracle UNIX
 Oracle Linux
 Remote s
 Remote plans
 Application Server

 Oracle Forms
 Oracle Portal
 App Upgrades
 SQL Server
 Oracle Concepts
 Software Support

 Remote S


 Consulting Staff
 Consulting Prices
 Help Wanted!


 Oracle Posters
 Oracle Books

 Oracle Scripts

Don Burleson Blog 








  Oracle Database Tips by Donald Burleson

Oracle10g Grid Computing with RAC
Chapter 7 - Cache Fusion and Inter Instance Coordination

Evolution of Cache Fusion

Requesting Instance  Dirty Block exists in Holding Instance    Cache Coherency Method
Instance     Holding
---------    --------  -------------------------------------      --------------------------
For Read   Write      No                                                        Soft Ping(read from disk)
For Read   Write      Yes                                                       Cache Fusion
For Write   Write      Does Not matter                                   Ping (force disk write)

Table 7.1 - The Methods of maintaining cache coherency

Oracle 8i (Oracle Parallel Server) had a background process called the block server process (BSP), which facilitated cache fusion. BSP was responsible for transferring the required blocks directly from the owning instance to the buffer cache of the requested instance.

For read/write operations, if the block was already written to disk by the holding instance, the requested block was read from the disk. It involved a soft ping or an I/O-less ping. If the block was available on the holding instance buffer, the BSP process prepared a consistent-read (CR) image of the data block. It was then sent to the requesting instance.

A write/write operation invariably involved the 'ping' of the data block. When the 'ping' occurred, the holding instance wrote to disk and downgraded the lock mode. Then, the requesting instance acquired the necessary lock mode and read from the disk. This frequent pinging hurt the performance of the OPS database. With the full implementation of cache fusion in release 9i, all these ping, soft ping, and false ping issues have been solved. With the RAC system release in 9i, cache fusion fully resolves write/write conflicts using the new architecture of resource coordination and global cache service.

Nature of Cache Fusion

Multi-node Oracle RAC systems are comprised of multiple instances with each instance residing on an individual node or server. Each Oracle instance in the cluster has a dedicated set of memory structures including background processes and system global areas (SGA) that exist irrespective of another node's instance. Thus, each node's instance has its local 'buffer cache.' When applications or users connect and process their SQL operations, they primarily connect to one of the nodes. When the user processes fetch and access data blocks, the scope of such activity is confined to the SGA of the connected instance.

However, as the database is mounted with multiple instances, data blocks may exist on any of the instances or any instance may fetch the data blocks as needed by the user processes. In other words, when a user process is looking for a set of data blocks to satisfy the SQL operation requirement, the same set of blocks or some of the blocks may already be available in another node's instance. This highlights an important fact of a RAC system. As opposed to a single stand-alone Oracle instance, there are multiple server locations in a RAC system where data blocks reside. Thus, there are several cache buffers dealing with the same physical database objects.

The above text is an excerpt from:

Oracle 10g Grid & Real Application Clusters
Oracle 10g Grid Computing with RAC
ISBN 0-9744355-4-6

by Mike Ault, Madhu Tumma


Oracle Training at Sea
oracle dba poster

Follow us on Twitter 
Oracle performance tuning software 
Oracle Linux poster


Burleson is the American Team

Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  

and include the URL for the page.


Burleson Consulting

The Oracle of Database Support

Oracle Performance Tuning

Remote DBA Services


Copyright © 1996 -  2020

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.