where the following is true:
-
max
- Maximum number of sessions to log on.
- The max specification must be greater than zero.
- The default, if the SESSIONS command is not used, is one session for each AMP.
-
min
- Minimum number of sessions required for the job to continue.
- The min specification must be greater than zero.
- The default, if the SESSIONS command is not used, is 1.
- *
- Minimum and maximum number of sessions.
- Using the asterisk character as the max specification logs on for the maximum number of sessions—one for each AMP.
- Using the asterisk character as the min specification logs on for at least one session, but less than or equal to the max specification.
Specifying SESSIONS * * has the same effect as not using the SESSIONS command at all.
On large to very large Teradata Database configurations, the default of one session per AMP may be inappropriate.
- There is no general method to determine the optimal number of sessions, because it is dependent on several factors, including, but not limited to:
- Teradata Database performance and workload
- Client platform type, performance, and workload
- Channel performance, for mainframe-attached systems
- Network topology and performance, for network-attached systems
- Volume of data to be processed by the application
- Using too few sessions is likely to unnecessarily limit throughput. On the other hand, using too many sessions can increase session management overhead (and also reduce the number of sessions available to any other applications) and may, in some circumstances, degrade throughput.
- Regardless of the size of the Teradata Database configuration, for large repetitive production applications, it will usually be appropriate to experiment with several different session configurations to determine the best trade-off between resource utilization and throughput performance.
- For larger Teradata Database configurations, it is appropriate to establish an installation default for the maximum number of sessions that is less than one session per AMP. This can be done either via the installation configuration file (see Teradata FastLoad Configuration File) or via a standard runtime parameter (see Mainframe-Attached Runtime Parameters). An installation default for number of sessions, if specified in the configuration file, can be overridden in individual Teradata FastLoad job scripts, when necessary.