IBM Tivoli Directory Server, Version 6.3


There are two alternative ways that Tivoli® Directory Server influences the DB2® optimizer to make better choice about how to access data in the LDAP tables. These are controlled by environment variables, as follows:

If LDAP_MAXCARD is set to YES and IBMDSLAPD_USE_SELECTIVITY is set to YES, the server will log a message and SELECTIVITY will not be used.

You can improve the performance of subtree searches on search bases that are high in a directory tree by using SELECTIVITY in Structured Query Language (SQL). The inclusion of SELECTIVITY in SQL enables the DB2 optimizer in the formation of access plans to resolve the search request (identifying which tables to access first during searches). Determination of the entries that are high in the tree (having a large number of children) is based on DB2 statistics. If a subtree search is done using one of these entries as the search base, the SELECTIVITY clause will be added to the SQL query. This causes DB2 to use the search filter to narrow down the search results before reading the table that identifies the entries that are descendants of a base in a search.

To use SELECTIVITY, the DB2 registry for the database instance must have DB2_SELECTIVITY set to YES. This is in addition to the environment variables described above. This is done when creating a database instance or while migrating from previous versions.

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