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
IBM Tivoli Monitoring, Version 6.3 Fix Pack 2
Terminology
The terms in this section are useful for understanding performance issues.
- Throughput
- The amount of data transferred from one place to another or processed in a specified amount of time. Data transfer rates for disk drives and networks are measured in terms of throughput. Typically, throughputs are measured in kilobytes per second, Mbps, and Gbps.
- Optimizer
- When an SQL statement is run, the SQL compiler must determine the access plan to the database tables. The optimizer creates this access plan, using information about the distribution of data in specific columns of tables and indexes if these columns are used to select rows or join tables. The optimizer uses this information to estimate the costs of alternative access plans for each query. Statistical information about the size of the database tables and available indexes heavily influences the optimizer estimates.
- Clustered Index
- An index whose sequence of key values closely corresponds to the sequence of rows that are stored in a table. Statistics that the optimizer uses measure the degree of this correspondence.
- Cardinality
- The number of rows in the table or for indexed columns the number of distinct values of that column in a table.
- Prefetch
- An operation in which data is read before its use when its use is anticipated. DB2 supports the following mechanisms:
- Sequential prefetch
- A mechanism that reads consecutive pages into the buffer pool before the application requires the pages.
- List prefetch or list sequential prefetch
- Prefetches a set of non-consecutive data pages efficiently.
Parent topic:
Relational database design and performance tuning for DB2 Database servers