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Gang Li & Yun Huang




Documentation of System Table


System tables uses to track the database objects. In essence, access is a set of relational database tables (the system tables) about a set of relational database tables (the user project). System tables should not be altered directly by any user. For example, do not attempt to modify system tables with DELETE, UPDATE, or INSERT statements, or user-defined triggers.

System tales are much like the tables you create in a database - with a few exceptions. First, they are identified internally as system objects so that you can differentiate your regular tables from system tables. Secondly, some system tables are inherently read-only. System table are documented here solely for the purpose of giving us a better understanding of how Teradata RDBMS works internally. The following table describes each of the system tables.

DBC.ACCESSRIGHTS
Describes each database and userid on the Teradata RDBMS.

DBC.AccLogTbl
Each time a user named in a BEGIN LOGGING statement attempts to execute a specified action against a specified object, Teradata performs one or more access-rights checks as defined by the rule(s) residing in DBC.AccLogRuleTbl. The completed check(s) generate one or more log entries in DBC.AccLogTbl.

The BEGIN LOGGING statement can request checks on one, all, or any combinations of the following:

The contents of DBC.AccLogTbl can be monitored via the The contents of DBC.AccessLog system view.

DBC.AccLogRuleTbl
The rules resulting from the execution of BEGIN LOGGING statements are entered in the system table DBC.AccLogRuleTbl

When access logging is active, Teradata looks in DBC.AccLogRuleTbl to determine which privilege checks should be made against a specified user, action, or object.

The END LOGGING statement is used to turn off the frequency and/or the text flag or a user, action, or object for which access rules are active. If this action turns off all logging rules for a particular user, database, or table, the row is deleted from DBC.AccLogRuleTbl.

The contents of DBC.AccLogRuleTbl can be monitored via the DBC.AccLogRuleTbl system view.

DBC.DBASE
Describes each database and userid on the Teradata RDBMS. Identify database.

DBC.INDEXES
Describes columns contained in indexes in the Teradata RDBMS.

DBC.ResUsage
Log resource usage data.

DBC.SessionTbl
Identify session. The DBC.SessionTbl table reflects the new account/priority for the current session. Performance data is collected on status of individual sessions. The LongonSource column of DBC.SessionTble table is affected by Performance Monitor (PM). This column includes additional information about the source of sessions logged on from an MVS or VM client, including information on the TDP and job name.

DBC.SW_Event_Log
The acccout/priority change is recorded in the DBC.SW_Event_Log table with the following text in the TEXT column:
SESSION session_no HOSTID host_id CHANGED FROM ACCOUNT account to ACCOUNT account ON sess_req.

The EVENT_TAG field contains an event number. THEDATE and THETIME fields, which comprise the index of the DBC.SW_Event_Log table, contain the date and time of the account/priority change. All other fields of the table are blank.

DBC.TVM
Describes each table, view, or macro on the Teradata RDBMS. Identify table.

DBC.TVFIELDS
Describes each column on the Teradata RDBMS.

DBC.User
Identify user.