The following table describes the things to consider when using the BEGIN EXPORT command.
Topic | Usage Notes |
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Command Placement and Frequency | The BEGIN EXPORT command must be the first command in a group of FastExport utility commands that specify an export task. Multiple BEGIN EXPORT commands can be used in a FastExport job script, but each export task specification must begin with a BEGIN EXPORT command and end with an END EXPORT command. |
Sessions Limit Specification | The number of sessions that you should specify depends on the connections to the database and the amount of data to be returned. In addition to the sessions that are used for the export task, FastExport uses two additional sessions to:
There is no general method to determine the optimal number of sessions, because it is dependent on several factors, including, but not limited, to:
When specifying the session limit, always consider the load that the export task is placing on the channel or network connection. For example, four sessions on a mainframe-attached system, each on a different interface processor (IFP) on a channel, and all concurrently returning data can saturate a single channel. In such a case, define the maximum number of sessions as four times the number of channels that are controlled by the Teradata Director Program (TDP) that connects the sessions. 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. If the minimum number of FastExport sessions are not logged, FastExport will terminate. Regardless of the size of the database system 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 database system configurations, it is appropriate to establish an installation default for the maximum number of sessions that is greater than four sessions, but less than one session per AMP. This can be done using an installation configuration file (see FastExport Configuration File) or a standard runtime parameter (see Runtime Parameters). An installation default for number of sessions, if specified in the configuration file, can be overridden in individual FastExport job scripts, when necessary. On large to very large database system configurations, the limit of one session per AMP when * is specified may be inappropriately large. |
Spool/NoSpool Modes | The NoSpool mode exports the contents of a table as fast as possible without reading the table into a spool file or distributing the file to all AMPs before extracting it. Three options for spooling are:
Possible scenarios for taking advantage of the NOSPOOL mode are as follows:
Limitations and functionality:
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