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There’s a comment on an earlier blog posting of mine from 2009 titled Controlling the Flow of Work in Teradata.  The comment poses a question that is more reasonably answered by making second posting on flow control. 

AMP worker tasks are the dedicated tasks inside each AMP that get the database work done.  As there are a limited number, this important resource is actively monitored by DBAs on busy systems.  TASM system-level events can take care of the monitoring for you, and based on a threshold you have set set, will trigger changes in workload management setup to manage the AWT shortage.  How AMP worker task events do their monitoring has changed in Teradata Database 13.10, and this posting describes those changes.

Statistical information is vital for the optimizer when it builds query plans.  But collecting statistics can involve time and resources.  By understanding and combining several different statistics gathering techniques, users of Teradata can find the correct balance between good query plans and the time required to ensure adequate statistical information is always available.

The following statistics collection recommendations are intended for sites that are on any of the Teradata 13.10 software release levels.  Most of these recommendations apply to releases earlier than Teradata 13.10, however some may be specific to Teradata 13.10 only.

Accurately identifying how much a table has grown since statistics on a column were last collected is an important prerequisite for the statistics extrapolation process.  Once table growth has been detected, then stale statistics can be adjusted accordingly.  Extrapolations based on table growth will be be more accurate if statistics are being regularly collected on the system-derived column PARTITON, whether or not a table is partitioned.

If you are a TASM user, there is an option that springs up when you create a workload, labeled Enforcement Priority. The option name sounds a little more intimidating than it actually is. I’d like to take this opportunity to explain what enforcement priority is, what it actually does, and what it doesn’t do, and just how seriously you should take it.

I know of a Teradata site that chose to use global temporary tables (GTTs) with their tactical queries in an attempt to get good performance against their fact table. However, there are some known limitations in doing that which I want to share with you. Read this posting to find out why mixing GTTs and tactical queries should not be your first choice.

Reserving AMP worker  tasks (AWT) for tactical applications is a technique to protect business-critical, short queries, when the platform is experiencing AMP worker task exhaustion.   If you are thinking about reserving AWTs, there are two different settings for which you will be required to provide values.  This posting discusses what these two settings are and how to be smart about setting them.

If you are using Teradata on one of the 1xxx or 2xxx platforms, be aware that query demotions are automatically built into your workload management scheme.   Because I’ve had a few questions about what these so-called "query milestones" are and how they actually work, I’d like to explain this functionality and discuss its trade-offs. 

The FastExport utility is usually seen as a batch-oriented job to use when you need to return large numbers of rows from the database to a user.   It is the ideal tool for efficiently and quickly returning large answer sets, sorted or otherwise, back to the client from the database.   That’s why it was named the way it was:  “FastExport”.  

It might surprise you that FastExport  can also be used against small data volumes.  And when it is, Teradata 13.10 includes an important enhancement that gives you a more efficient way to get those rows back quickly.

Have you ever wondered how many AMP worker tasks (AWT) were actually being used during an archive or a restore?  You're not alone.  Is it one per session?  Could it be one per AMP?  Here's how it works.

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