Rac Architecture Overview

RAC Architecture

Oracle Real Application clusters allows multiple instances to access a single database, the instances will be running on multiple nodes. In an standard Oracle configuration a database can only be mounted by one instance but in a RAC environment many instances can access a single database. 

Oracle's RAC is heavy dependent on a efficient, high reliable high speed private network called the interconnect, make sure when designing a RAC system that you get the best that you can afford.

The table below describes the difference of a standard oracle database (single instance) an a RAC environment

Component	Single Instance Environment	RAC Environment
SGA	Instance has its own SGA	Each instance has its own SGA
Background processes	Instance has its own set of background processes	Each instance has its own set of background processes
Datafiles	Accessed by only one instance	Shared by all instances (shared storage)
Control Files	Accessed by only one instance	Shared by all instances (shared storage)
Online Redo Logfile	Dedicated for write/read to only one instance	Only one instance can write but other instances can read during recovery and archiving. If an instance is shutdown, log switches by other instances can force the idle instance redo logs to be archived
Archived Redo Logfile	Dedicated to the instance	Private to the instance but other instances will need access to all required archive logs during media recovery
Flash Recovery Log	Accessed by only one instance	Shared by all instances (shared storage)
Alert Log and Trace Files	Dedicated to the instance	Private to each instance, other instances never read or write to those files.
ORACLE_HOME	Multiple instances on the same server accessing different databases ca use the same executable files	Same as single instance plus can be placed on shared file system allowing a common ORACLE_HOME for all instances in a RAC environment.

RAC Components
The major components of a Oracle RAC system are

• Shared disk system
• Oracle Clusterware
• Cluster Interconnects
• Oracle Kernel Components

The below diagram describes the basic architecture of the Oracle RAC environment

Here are a list of processes running on a freshly installed RAC

Next updation soon.

Thanks

Ravi Kr Shrivastava

Senior Oracle DBA

Tablespace Used Free Space "Amazing"

Hi Buddy,

Use this script. This Will Definetly Help the DBA.

*TABLESPACE USED FREE %USED % FREE AND AUTOEXTENSIBLE SCRIPT*

*****************************************************************

set linesize 200
column F_NAME format a38
column TABLESPACE format a15
set pagesize 400

 select t.tablespace,F_NAME,auto,MAX_GB,t.totalspace as " Total_MB", round((t.totalspace-fs.freespace),2) as "Used_MB", fs.freespace as "Free_MB", round(((t.totalspace-fs.freespace)/t.totalspace)*100,2) as "%Used", round((fs.freespace/t.totalspace)*100,2) as "% Free" from (select round(sum(d.bytes)/(1024*1024)) as totalspace, d.tablespace_name tablespace,d.autoextensible as auto,d.file_name as F_NAME,round(sum(d.maxbytes)/(1024*1024*1024))as MAX_GB  from dba_data_files d group by d.tablespace_name,d.autoextensible,d.file_name) t,(select round(sum(f.bytes)/(1024*1024)) as freespace, f.tablespace_name tablespace from dba_free_space f group by f.tablespace_name) fs where t.tablespace=fs.tablespace order by t.tablespace;

Thanks

Ravi Kr Shrivastava

Senior Oracle DBA.