15.00 - Protecting a Join Index with Fallback - Teradata Database

Teradata Database Design

prodname
Teradata Database
vrm_release
15.00
category
User Guide
featnum
B035-1094-015K

Protecting a Join Index with Fallback

You can define fallback protection for a simple or aggregate join index.

With fallback, you can access a join index and the base table it references if an AMP fails, with little impact on performance.

Without fallback, an AMP failure has significant impact on both availability and performance as follows.

  • You cannot update the base table referenced by a join index even if that base table is defined with fallback.
  • The Optimizer cannot access a join index on a down AMP to create query plans. Performance can be degraded significantly when this occurs.
  • The cost of having fallback for a join index when executing a DML request that modifies a base table referenced by the join index is a slight increase in processing to maintain the fallback copy of the join index.