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

Concurrency and Consistency

  1. Concurrent reads on multiple instances - When users on two different instances need to read the same set of blocks.

2. Concurrent reads and writes on different instances - A user intends to read a data block that was recently modified, and the read can be for the current version of the block or for a read-consistent previous version.

3. Concurrent writes on different instances - When the same set of data blocks are modified by different users on different instances.

Cache Coherency

Whether the database is a single-instance stand-alone system or a multi-instance RAC system, maintaining data consistency is a fundamental requirement. If data blocks are already available in the local buffer cache, then they are immediately available for user processes. And, if they are available in another instance within the cluster, they will be transferred into the local buffer cache.

Maintaining the consistency of data blocks in the buffer caches of multiple instances is called 'cache coherency'. The global cache service (GCS), implemented by a set of Oracle processes requires an instance to acquire cluster-wide data before a block can be modified or read. In this way, cache coherency is ensured and maintained. This resource can be explained in terms of enqueue and/or lock.

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.