IBM Tivoli Monitoring > Version 6.3 Fix Pack 2 > Installation Guides > Installation Guide > Performance tuning > Tivoli Data Warehouse > Relational database design and performance tuning for DB2 Database servers > Tuning
IBM Tivoli Monitoring, Version 6.3 Fix Pack 2
Registry variables
Each instance of the database manager has a set of registry and environment variables that affect various aspects of DB2 processing. You can change the value of DB2 registry variables using the DB2SET command. Although numerous other registry and environment variables exist, the DB2_PARALLEL_IO variable has a high impact on performance.
See the DB2 Administration Guide: Performance for a detailed explanation of all the registry and environment variables.
While reading or writing data from and to table space containers, DB2 may use parallel I/O for each table space value that you specify. The prefetch size and extent size for the containers in the table space determine the degree of parallelism. For example, if the prefetch size is four times the extent size, there are four extent-sized prefetch requests. The number of containers in the table space does not affect the number of prefetchers.
To enable parallel I/O for all table spaces, you can specify the asterisk (*) wildcard character. To enable parallel I/O for a subset of all table spaces, enter the list of table spaces. For several containers, extent-size pieces of any full prefetch request are broken down into smaller requests that are executed in parallel based on the number of prefetchers. When this variable is not enabled, the number of containers in the table space determines the number of prefetcher requests that are created.
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Tuning