16.20 - Identity Column Inserts and Transaction-Bound Table Locks on DBC.IdCol - Teradata Database - Teradata Vantage NewSQL Engine

Teradata Vantage™ SQL Data Definition Language Detailed Topics

Product
Teradata Database
Teradata Vantage NewSQL Engine
Release Number
16.20
Release Date
March 2019
Content Type
Programming Reference
Publication ID
B035-1184-162K
Language
English (United States)
An identity column cache is populated by a range of column numbers whenever an INSERT operation into an identity column table is processed. The values for the range are determined by the following factors.
  • The next available value stored in DBC.IdCol.AvailValue
  • The defined incremental identity column batch size for the system

    This quantity is specified by the DBS Control parameter IdCol batch size. For more information, see Teradata Vantage™ - Database Utilities , B035-1102 and Optimizing Bulk Inserts Into an Identity Column.

When the pool of available identity column numbers in the cache is exhausted, Teradata Database must update DBC.IdCol.AvailValue and obtain a new range of numbers.

If an ongoing transaction has DBC.IdCol locked, as it would during a SELECT statement against the table, then system access to the column number pool is temporarily blocked and all inserts into the relevant identity column table are suspended until the transaction either commits or aborts. A SELECT statement against DBC.IdCol places an ACCESS lock on the table.

The SELECT privilege on DBC.IdCol is restricted to user DBC and any user explicitly granted the privilege by DBC.

When performing a SELECT statement against DBC.IdCol in Teradata session mode, you run the risk of creating a deadlock if you upgrade the default lock from ACCESS to READ or higher severity when both of the following conditions are true.
  • The SELECT statement is run within the boundaries of an explicit transaction.
  • Concurrent INSERT operations are being performed on an identity column table.