16.10 - System Tables Subject to Skewing - Teradata Database

Teradata Database Administration

Product
Teradata Database
Release Number
16.10
Release Date
April 2018
Content Type
Administration
Publication ID
B035-1093-161K
Language
English (United States)
  • Journal tables take the require spool and other transient storage from free space. A common practice is to allocate a database with a certain amount of PERM, but never use it. This ensures that there is free space for journals and so on. When your journal tables are skewed, you get an error when running queries, letting you know the system needs the journal space but cannot obtain it.
  • The DBC.AccessRights table is notorious for becoming skewed. If it grows too large, it will affect the space limits dramatically. To reduce this skewing, either clean up DBC.AccessRights by removing redundant rows or convert to using roles and then remove the now redundant rows.
  • DBC.AccLogTbl table. Teradata Database generates at least one entry every time a user defined for logging attempts to access an object. This table can grow very large and consume a lot of disk space.
  • Resource usage logging tables or query logging tables. Consider daily offloading data from the actual DBC tables into temporary staging tables and ultimately history tables for analysis or archive.

Any table can becoming skewed if the primary index is poorly designed or if statistics have not been collected and the Optimizer is using stale data. A usual tell-tale sign is if one or more queries are doing a lot of maintenance on typically a single AMP. If this happens, you need to track that query down and handle it like any other skewed processing.