Tables may stay the same size after being created or change frequently. A table must use a map that has the number of AMPs appropriate to the table size, which leads to an even distribution of the table rows among the AMPs in the map. Periodically reassess a table to make sure that the table uses a map appropriate for the current size and for expected growth.
Here are scenarios in which a DBA may want to use maps to move table data from one set of AMPs to another.
System Expansion
After you add AMPs or nodes to a system, if MAPS architecture is enabled, the Reconfiguration utility (Reconfig) creates a new map that reflects the expanded system. A DBA can then move table rows to the new AMPs using Reconfig or MAPS. There are advantages to using MAPS instead of Reconfig:
- Reconfig requires more planned downtime.
- Reconfig requires you to move all tables in the system immediately to evenly distribute rows between AMPs. However, if you use MAPS, you can move tables into the new configuration gradually while the system is online. You can have tables in the old map and tables can be in the new, expanded map.
- The Configuration and Reconfiguration utilities must be run under the supervision of Teradata Support personnel.
- You can also use the MAPS Advisor procedures to model the moves before a system expansion. You can redo the analysis as often as needed.
Upgrade
When you upgrade your system to Release 16.10 or later and enable Teradata MAPS architecture, look for small tables that can benefit from using a sparse map.