Scenario | Teradata Director Program - Scenario - Teradata Director Program

Teradata® Director Program Reference - 17.20

Deployment
VantageCloud
VantageCore
Edition
Enterprise
IntelliFlex
Lake
VMware
Product
Teradata Director Program
Release Number
17.20
Published
June 2022
Language
English (United States)
Last Update
2023-11-17
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Product Category
Teradata Tools and Utilities

Suppose a customer has been getting TDP0021 warnings for 992 byte cells (data buffers), for example:

TDP0021 **WARNING** 100% OF 992 BYTE CELLS IN USE

The maximum number of data buffers required is equal to the product of the number of sessions and the amount of data transferred divided by 992:

((number of sessions)(amount of data transferred))/992

The amount of data transferred applies to both requests and responses.

For all but the most unusual cases, using this maximum number of data buffers is unnecessary. Cell usage can push the maximum in cases where the ratio of interface processors to AMPs on the system is very low (for example, 8:104). In this case, data transfer through the interface processor is a bottleneck because each session sends a request into TDP, and those requests become enqueued within TDP because the bottleneck restricts TDP’s ability to dispatch the requests to the database in a timely way.

This creates a “producer-consumer” relationship in which the sessions produce requests (up to 32K each in the case of FastLoad) that are buffered in TDP until the database can consume them. The interface processor bottleneck represents slow consumption, and more data ends up buffered in TDP than would normally occur.

More commonly, the sessions communicating through TDP might, at any given instant, be in one of several states. These states include:
  • Request inside TDP waiting for I/O to the database (Requires TDP cells)
  • Request active on the database (Does not require cells)
  • Response received in TDP but not yet sent to the application (Requires cells)
  • Response sent to the application, but next request has not yet arrived (Does not require cells)

At any given moment, the number of sessions whose request is within TDP but has not yet been sent to the database is less than or equal to the total number of sessions logged on. Set the number of cells more than the average, but less the peak. Average and peak are functions of the configuration and the workload. For example, running five FastLoad jobs and several BulkLoad jobs on the database with eight interface processors and 104 AMPs produces a much higher average percent of sessions with requests/responses passing through TDP than would a sixteen interface processor, 104 AMP database system.

The optimal way to handle standard use is to set the number of cells just more than the average and then let TDP memory management algorithm deal with peak activity periods because it is generally neither practical nor beneficial to give TDP the number of cells required to handle peak requests. Generally, it is better to let requests back up in the application address space instead. Such an approach should provide equal or better throughput while at the same time ensure better usage of CPU and real storage consumption by the operating system.

The message noted at the beginning of this section, the TDP0021 message, indicates the percentage of available cells that are in use. Peaks of 100% are not cause for alarm, though an average of 100% indicates that more cells should be added. In general, assume that somewhere between 20 and 30 percent of the sessions active are inside TDP at any given moment.