Some tables stay the same size after they are created, while others change frequently. A table should 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. Consequently, it is a good idea to periodically reassess a table to ensure that it uses a map appropriate for the current size and for expected growth.
There are several scenarios in which a DBA might want to use maps to move table data from one set of AMPs to another.
- 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. Some tables can be in the old map and some tables can be in the new, expanded map.
When you upgrade your system to Release 16.10 or later and you enable Teradata Database MAPS architecture, you can look for small tables that would benefit from using a sparse map.
As you add new tables to your system, you may occasionally want to analyze whether tables are placed on AMPs for maximum efficiency.