Oracle RAC

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In database computing, Oracle Real Application Clusters (RAC) — an option[1] for the Oracle Database software produced by Oracle Corporation and introduced in 2001 with Oracle9i — provides software for clustering and high availability in Oracle database environments. Oracle Corporation includes RAC with the Standard Edition, provided the nodes are clustered using Oracle Clusterware.[2]




In an Oracle RAC environment, 2 or more computers (each with an Oracle RDBMS instance) concurrently access a single database. This allows an application or user to connect to either computer and have access to a single coordinated set of data.




Oracle RAC depends on the infrastructure component Oracle Clusterware to coordinate multiple servers and their sharing of data storage.[3] The FAN (Fast Application Notification) technology detects down-states.[4] RAC administrators can use the srvctl tool to manage RAC configurations,[5]

Cache Fusion[edit]


Since all computers/instances in a RAC access the same database, the overall system must guarantee the coordination of data changes on different computers such that whenever a computer queries data, it receives the current version — even if another computer recently modified that data. Oracle RAC refers to this functionality as Cache Fusion. Cache Fusion involves the ability of Oracle RAC to "fuse" the in-memory data cached physically separately on each computer into a single, global cache.







The overhead on the resource mastering (or ownership-transfer) is minimal for fewer than three nodes, as the request for any resource in the cluster can be obtained in a maximum of three hops (owner-master-requestor).[citation needed] This makes Oracle RAC horizontally scalable with many nodes. Application vendors (such as SAP) use Oracle RAC to demonstrate the scalability of their application. Most of the biggest OLTP benchmarks are on Oracle RAC. Oracle RAC 11g supports up to 100 nodes.[7]


Competitive context[edit]

Shared-nothing and shared-everything architectures each have advantages over the other. DBMS vendors and industry analysts regularly debate the matter; for example, Microsoft touts a comparison of its SQL Server 2005 with Oracle 10g RAC.[8]

Oracle Corporation offered a Shared Nothing architecture RDBMS with the advent of the IBM SP and SP2 with the release of 7.x MPP editions, in which virtual shared drives (VSD) were used to create a Shared Everything implementation on a Shared Nothing architecture.


"Shared-everything" architectures share both data on disk and data in memory between nodes in the cluster. This is in contrast to "shared-nothing" architectures that share none of them.

Some commercially-available databases offer a "shared-everything" architecture. IBM DB2 for z/OS (the IBM mainframe operating-system) has provided a high-performance data-sharing option since the mid-1990s when IBM released its mainframe hardware and software-clustering infrastructure. In late 2009, IBM announced DB2 pureScale, a shared-disk clustering scheme for DB2 9.8 on AIX that mimics the parallel sysplex implementation behind DB2 data sharing on the mainframe.

In February 2008, Sybase released its Adaptive Server Enterprise, Cluster Edition. It resembles Oracle RAC in its shared-everything design.[9]

Although technically not shared-everything, Sybase also provides a column-based relational database focused on analytic and datawarehouse applications called Sybase IQ that can be configured to run in a shared disk mode.


"Shared-nothing" architectures share neither the data on disk nor the data in memory between nodes in the cluster. This is in contrast to "shared-everything" architectures, which share both.

Competitive products offering shared-nothing architectures include:

See also[edit]


  1. ^ Options and Packs
  2. ^ Oracle Database Editions
  3. ^ Introduction to Oracle Real Application Clusters
  4. ^ Mensah, Kuassi (2006). Oracle database programming using Java and Web services. Digital Press. p. 1087. ISBN 978-1-55558-329-3. Retrieved 2011-09-11. "The Fast Application Notification (FAN) mechanism [...] allows the rapid detection of "Instance DOWN" or "Node DOWN events [...]" 
  5. ^ Stoever, Edward (2006). Personal Oracle RAC Clusters: Create Oracle 10g Grid Computing At Home. Oracle In-focus Series. Rampant TechPress. p. 119. ISBN 9780976157380. Retrieved 2013-05-30. "An RAC database configuration requires extra tools to manage the software and its instances. One such tool is srvctl, used to startup, shutdown and check the status [of] a RAC database." 
  6. ^ "Oracle Real Application Clusters One Node: Better Virtualization for Databases". Find White Papers. 2009-12-09. Retrieved 2010-04-19. "Oracle RAC One Node provides: . Always on single-instance database services . Better consolidation for database servers . Enhanced server virtualization . [,,,] should the need arise, upgrade to a full multi-node Oracle RAC database without downtime or disruption. [...] Oracle Real Application Clusters (RAC) One Node is a new option to Oracle Database 11g Release 2 Enterprise Edition. It provides enhanced high availability for singleinstance databases," 
  7. ^ "clustering". Retrieved 2012-11-07. 
  8. ^ Thomas, Bryan (2006-05-30). "Solutions for Highly Scalable Database Applications: An analysis of architectures and technologies" (PDF). Microsoft. Retrieved 2007-09-09. 
  9. ^ "". Retrieved 2012-11-07. 
  10. ^ "Oracle buys Finnish open-source developer". InfoWorld. October 7, 2005.  "Oracle Buys SUN; MySQL is Forked". Linux Magazine. April 20, 2009. 

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