Saturday, 24 August 2013

DB2 Directory

The DB2 directory is used to store information about the operation and housekeeping of the DB2 environment. This directory, unlike the DB2 catalog, cannot be accessed by using SQL.
The DB2 directory contains information required to start DB2; activities and utilities in the DB2 environment do the updating and deleting of table entries in the DB2 directory.
Directory Table
Information Contents
Referred to as the skeleton package table (SKPT), this table contains information about the access paths and the internal form of the SQL for a package at bind time. Entries are made into this table during bind time (BIND PACKAGE), and entries are deleted when a package is freed (FREE PACKAGE). This table is loaded into memory at execution time, along with the SCT02 table described next.
Referred to as the skeleton cursor table (SKCT), this table contains information about access paths and the internal form of the SQL for an application plan. Entries in this table are made when a plan is bound (BIND PLAN) and deleted when a plan is freed (FREE PLAN). This table is also loaded into memory at execution time.
Information about DBDs (database descriptors), which are internal control blocks, is kept in this table. Each DB2 database has one DBD for its objects: table spaces, indexes, tables, referential integrity constraints, and check constraints. Updates to this table are made when a database is created or updated. This information is accessed by DB2 in place of continually using the DB2 catalog, permitting faster, more efficient access to this information. The information in the DBD01 directory table is also contained in the DB2 catalog.
Referred to as the log range table, this table contains information from the DB2 logs about the RBA (relative byte address) range for updates. This allows DB2 to efficiently find the RBAs needed from the DB2 logs for recovery purposes. A row is inserted every time a table space or a partition is opened or updated and is updated when the object is closed.
This system utilities table stores information about the execution of DB2 utilities, including the status and the steps during execution. This information is used when a utility needs to be restarted. Information in this table is added when a utility is started, and the entry is removed when the execution has ended.

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