Online and Offline Reconfiguration
Portions of the reconfiguration process require that no users be logged on to Teradata Database, and that the system be quiescent. Reconfiguration ends with a system restart. During these phases, the system is unavailable to users.
Optionally, a large portion of reconfiguration can occur while users remain logged on to the system. This process is called online reconfiguration, and can greatly increase system availability during reconfiguration.
Note: Online reconfiguration does not support move AMP, delete AMP, and hash bucket size change operations.
A special reconfiguration change log keeps track of changes to rows that will be moved to new AMPs as a result of the reconfiguration. (When the transaction journal is purged, table updates are written to the change log.) This allows the changes to be reapplied to the rows after they have been moved. Note the disk space recommendations described in “Disk Space for Reconfiguration” on page 247.
Offline reconfiguration is that portion of reconfiguration that happens when all users are logged off the system, and the system is quiescent. When the entire reconfiguration process is run offline, the overall reconfiguration can complete more quickly. However, the system typically will be unavailable to users for a much longer period of time than for a comparable reconfiguration that uses online reconfiguration.
Both online and offline reconfiguration allow user specification of the order in which tables are processed. Teradata recommends explicit specification of this order. If an ordering is not explicitly specified, tables are processed in table ID order. You specify the order by inserting rows into special system tables that exist for that purpose. These tables are described below.