Oracle Data Warehouses in a RAC Environment Oracle Database Tips by Donald Burleson

2014 Update:  Please see these 2015 updates to Oracle hardware architectures and the costs and benefits of server deconsolidation.

While Oracle Real Application Clusters (RAC) is not the ideal hardware architecture for Oracle data warehouse applications, some shops require the robust features of RAC for their data warehouse applications.

Generally, only shops that need 100% continuous availability or fast scalability choose RAC for a data warehouse, primarily because of the huge licensing costs and human effort required for proper installation and configuration. 

http://www.dba-oracle.com/t_rac_clusters_data_warehouse.htm

Oracle RAC is not the best solution to data warehouse applications because they require large banks of CPU's to perform parallel table-scan operations.  Mike Ault, noted Oracle data warehouse consultant notes "I have never heard of any shop using RAC for a data warehouse, and I could imaging large parallel operations clobbering the interconnect as to make RAC somewhat sub-optimal for data warehouse processing".

Unlike a monolithic data server where CPU and RAM resources are allocated automatically, Oracle RAC systems must have manual load balancing mechanisms to distribute the load across the server blades.

The costs of RAC

Oracle RAC is expensive to purchase and even more expensive to configure, especially in a data warehouse environment.  It is not uncommon to spend weeks of DBA effort allocating data warehouse ETL and aggregation jobs to minimize the impact and load balance between the server blades. 

Transparent Application Failover Configuration

We have many choices for RAC failover, each with differing complexity and overhead, depending on the needs of the COHORT users.  My article from Oracle Magazine, explains these issues:

http://www.dba-oracle.com/art_oramag_rac_taf.htm

Parallel Query in RAC

Especially challenging will be the parallel parallelism that is required to implement super-fast rollups in a massively-parallel environment, a task that can take a week or more to test and configure.

http://www.dba-oracle.com/art_builder_opq_cpu.htm

RAC load balancing

We also have to manage load-balancing for RAC, and this involves extensive manual configuration to use a round-robin configuration to distribute the load among the instances.  Starting in Oracle 10g release 2, we have a brand-new load-balancing advisory that promises to cut-down the manual effort for RAC load balancing between instances:

Time estimates for RAC configuration

It is highly recommended that COHORT utilize Oracle 10g release 2 RAC because of the improved RAC load-balancing automation which can save thousands of dollars,  Here are time estimates for a seasoned Oracle RAC DBA Consultant (with experience installing RAC on dozens of environments) for a typical RAC install and configuration.  A certified DBA without experience may take double these numbers:

Because an experienced  Oracle RAC consultant is more productive, many corporations outsource the RAC installation and configuration to Oracle consultancies such as Burleson Consulting..

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