Read Requests for Managed Routing | Teradata Unity - 17.00 - Read Requests for Managed Routing - Continuous Availability - Teradata Unity

Teradata® Unity™ User Guide

Product
Continuous Availability
Teradata Unity
Release Number
17.00
Published
September 2020
Language
English (United States)
Last Update
2020-09-15
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Unity routes session read requests to a single database system. If no routing rules are defined for a client logon, Unity provides a default routing rule (DefaultRouting).

When the requested data resides in tables on a subset of database systems, the Sequencer determines which database systems have all of the tables requested in the read operation.

The algorithm selected for routing depends on both the routing rule specific to the session client logon and current system and table states. Only tables in active or read-only state are available for reading. If there are no tables in active or read-only state, but one or more tables are in standby state, then Unity uses one of the tables in standby state for the read operation.

In a managed routing session, Unity load balances incoming read requests across all systems that have the needed tables. Unity keeps track of the number of outstanding requests on each system and sends the next read to the system with the least number of outstanding requests. Unity includes the EnableIncludeReadsInLBQ configuration setting. If set to true, the count of outstanding reads is included in the count of outstanding requests for load balancing in managed sessions. If set to false, only the outstanding writes are counted.