Day 1 : Introduction to RAC

What is RAC?

  

RAC stands for Real Application cluster. It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance failover, media failover features.

 

Why Do Users recomend RAC? Users may recomend RAC to achieve?

• Increasing availability
• Increasing scalability
• Improving maintainability
• Reduction in total cost of ownership

Why Do DBAs Deploy RAC?

• Realistic next step for experienced Oracle DBAs
• Intellectual challenge
• Job protection – ties organisation to Oracle technology
• Possible improved earnings
• It looks good on their CV

Why Do oracle recommend RAC?

 

• Commodity processing is cheap
• Downtime is expensive
• Incremental scalability is a huge win
• For marketing their product and to get good benifit.

What is a Cluster?

 

A cluster is a group of servers that act in concert to provide some combination of:

• Improved reliability
• Improved scalability
• Reduced processing costs

What is Clustering?

 

•   A Cluster is a collection of networked computers working together to form a single logical machine.
•  Cluster nodes are typically connected to each other through a fast network connection on a local area network within a small geographical site such as a building or a cluster of buildings: This is the norm., however there are exceptions to this rule with Extended Distance Clusters existing over WANs as well.
•  Having redundant nodes within a cluster provides for a continuous availability of computing services, as well as providing for more processing power to balance the computing load amongst several nodes instead of a single expensive powerful machine.
• Clustering is also Known-as/Synonymous-to Massive Parallel Processing (MPP)

 

Clustering Technologies

• Shared-nothing – Each cluster node has no common resource with any other node
• Shared-everything – Each cluster node shares a universal pool of common resources
• Shared-something – Each cluster node shares some resources, but not others
• Active-Passive – Only one cluster node at a time is providing any given service

Define Oracle Real Application Clusters?

 

 Oracle RAC is a “shared-something” cluster •

RAC nodes share:

–Application state awareness (Cache Fusion)

– A single set of on-disk data (ASM, OCFS, etc.)

• RAC provides

– Enhanced reliability

– Enhanced scalability

– Reduced processing cost

 

List the advantages/Benefits of using RAC

 

• Scalability
• High Availability
• Transparency
• Buffer Cache Management
• Row locking
• Multi Version Read Consistancy
• Reduction of Downtime
• Load Balancing / Workload Distribution

 

Differences between a single instance stand-alone configuration and a RAC database.

 

 

#	Single Instance	Real Application Cluster
1	One Instance maps to a single database	Two or more instances share a common physical database
2	Can run on a single processor hardware configuration or a multi processor configuration. However requires only a single node or machine for implementation.	Can also run on a single processor hardware configuration or a multi-processor configuration. However requires a hardware clustering and a clustered operating system.
3	Consists of one System Global Area and a set of background and foreground processes	Each and every instance requires it’s own System Global Area (SGA) (to store instance specific information), and background and foreground processes. It also consists of additional background processes like LMS and GCS.
4	One copy of the physical database and redo log files	Separate copies of redo logs and archive logs are maintained for every instance.
5	With just one instance attached to one copy of the physical database, no instance level synchronization is required.	Multi node synchronization is required. Synchronization between instances is using the cache fusion technology via the cluster interconnect.
6	V$ views to monitor and manage instance	V$ views are available and provide visibility to a single instance level information. For monitoring at the cluster level Oracle provides GV$ views.
7	Meeting some of the business requirements (availability, scalability) is limited to a single instance configuration.	Modern business requirements of high availability and linear scalability are provided by multiple instances sharing a common physical database.

 

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