Oracle -RAC Cache Fusion Technology

Cache Fusion, as it indicates it is fusing the memory buffer cache of multiple instance into one single cache what is called as global cache.

The High speed interconnect is used to share data in the memory i.e in the buffer cache of each instance.

To Understand the working of the global cache fusion we will look at the following terms

1) Global Resouce Directory

Global Resource Directory or GRD, kind of in-memory database contains details about all the blocks that are present in cache, version of the block, mode of the block
role of the block, whenever any user ask for block GCS get all the information from GRD.

All the participating instances maintain part of GRD.

Precisely GRD Contains following information

1) Data Block Address
2) Location of most current version of the Data Block
3) Modes of the Data Block
4) Roles of the Data Block
5) SCN of the Data Block
6) Image of the Data Block.

These Two component maintain the GRD (Global Resource Directory)

      1) Global Cache Service

Global Cache Service is the main component of the Cache Fusion Technology represented by LMSn Process, there can be upto 10 LMS process for an instance
Function of GCS is to track status of Data Block (Mode and Roles) and its also responsible for Block Transfer between instances.

LMS is the main process of it

      2) Global Enque Service

This Tracks  status of all Oracle Enqueuing Mechanism. Performs Concurrency control on dictionary cache locks, library cache locks and transactions.

4) GCS Resource Modes and roles


List Of Processes You can find on RAC System.

ACMS - Atomic controlfile to memroy service
GTX0-j   Global Transaction Process
LMON - Global Enqueue service monitor
LMD   -  Global Enqueue service Daemon
LMS  - Global Cache Service Process
LCK0 - Instance Enqueue Process
RMSn - Oracle RAC Management Process
RSMN  Remote Slave Monitor