15.10 - Setting Values for the MaxSessions Attribute - Parallel Transporter

Teradata Parallel Transporter User Guide

Parallel Transporter
User Guide

Setting Values for the MaxSessions Attribute

Consider the following factors when specifying a value for the MaxSessions attribute:

  • If no value is set for MaxSessions, the operator attempts to connect to one session per available AMP.
  • The DDL, ODBC, and SQL Selector operators are limited to a single concurrent session, that is, one session each per single-step job, or one each session per step in a multi-step job.
  • If the value of the MaxSessions attribute for an operator is smaller than the number of operator instances, the job will abort.
  • If the value of MaxSessions is set to a number greater than the number of available AMPs, the job runs successfully, but logs on only as many sessions as available AMPs.
  • For some jobs, especially those running on systems with a large number of AMPS, the default session allocation (one per available Teradata Database system AMP) may not be advantageous, and you may need to adjust the MaxSessions attribute value to limit the number of sessions used. After the job has run, use the evaluation criteria shown in “Strategies for Balancing Sessions and Instances” on page 85 to help adjust and optimize the MaxSessions setting.
  • The SQL Inserter operator supports only one session.
  • The Stream operator uses an SQL protocol, so it is not seen as a “load job” by the Teradata Database. Therefore, Stream operator connects to as many sessions as requested, up to the number of sessions allowed by the Teradata Database.
  • The Effect of Operator Instances on the MaxSessions Value

    The number of sessions specified by the value of the operator MaxSessions attribute are balanced across the number of operator instances. For example, if the Update operator is defined with two instances, and the MaxSessions attribute is set to 4, each instance of the defined Update operator will run two sessions, provided there are at least four AMPs on the system.

    An Update operator uses a maximum of one session per available AMP on the Teradata Database system. This means that if your Teradata Database system has ten available AMPs, the MaxSessions value must be less than or equal to ten.

    Examples of How the MaxSessions Value is Processed

    If there are ten maximum sessions defined for an operator, the following combinations of instances and sessions are possible:

  • One instance with ten sessions
  • Two instances with five sessions each
  • Three instances: two instances with three sessions and one instance with four sessions
  • Four instances: two instances with three sessions and two instances with two sessions
  • Five instances with two sessions each