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NOUG Session: How Cache Fusion Works

For all those attended my session at Northeast Oracle User Group at Babson College in Wellesley, MA. Have you ever wondered how Cache Fusion knows where to get the block from? Or, how block locks vary from row locks? Or you are confused about the meaning and purpose of various Global Cache Service (GCS), Global Resource Directory (GRD) and Global Enqueue Service (GES). The session was meant to explain how all these actually work under the covers with live demos.

Troubleshooting ‘DFS lock handle’ waits

Waits for ‘DFS lock handle’ can cause massive performance issues in a busy RAC cluster. In this blog entry, we will explore the DFS lock handle wait event, and understand how to troubleshoot the root cause of these waits. I am also going to use locks and resources interchangeably in this blog, but internally, they are two different types of structures.

A little background

DFS (stands for Distributed File System) is an ancient name, associated with cluster file system operations, in a Lock manager supplied by vendors in Oracle Parallel Server Environment (prior name for RAC). But, this wait event has morphed and is now associated with waits irrelevant to database files also. Hence, it is imperative to understand the underlying details to debug the ‘DFS lock handle’ waits.

How does it work?

Webcast: Under the Hoods of Cache Fusion for LAOUG and NZOUG

Many thanks to all those who attended my webcast - Under the Hoods of Cache Fusion - for the Latin American and New Zealand Oracle User Groups on July 22nd, 2010. I'm sure the user groups will host the recording of the event on their websites. As I mentioned in my call, you can download the scripts I used here.

I hope you have enjoyed the session and found it useful. As always, I appreciate your feedback, critique and suggestions. You can either post here as comments or send me an email at

RACSIG Webcast on June 24th Files

Thank you all those who attended my presentation - "Under the Hoods: Cache Fusion, GCS, GES and GRD". I hope you found it useful. Here are the demo scripts I used during the session, if you want to play with on your own system.

The actual presentation itself will most likely be available at a later date on the website.