Enforcement Priority: Soft, Hard, or Just Window-Dressing?

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.

There are four enforcement priorities, and every workload you define must be assigned one of those four. Enforcement priority doesn’t have anything to do with how resources are allocated, neither does it provide a priority boost to the more important work, at least not directly (I’ll explain what I mean by “not directly” a little further down). Rather, it is a way of for you to characterize and label the relative importance of the work running in that workload.

The four enforcement priorities to choose from include:

1. Tactical: For very short, critical queries that have a defined service level expectation.
2. Priority: For important work that needs to complete more quickly than most other work.
3. Normal: For average priority work (the default).
4. Background: For work that doesn’t have a response time requirement

In Viewpoint Workload Designer, select the General tab under Workload and you can see where to establish enforcement priority for a workload.

For the most part, enforcement priorities are passive. They are a method of grouping workloads with similar importance. Viewpoint uses enforcement priority to group and report on workloads, for example. However, there are a couple of ways in which they play an active role:

• Priority scheduler allocation groups support multiple workloads only when they have common enforcement priorities: You are only allowed to map multiple workloads to the same priority scheduler allocation group if those workloads share the same enforcement priority. If you have an allocation group with a relative weight of 15% and you have assigned a workload with a Priority enforcement priority to that allocation group, you are then prohibited from mapping a different workload to that allocation group unless it also has been defined with an enforcement priority of Priority.

• Special performance advantages to workloads with Tactical enforcement priorities. An additional active role for enforcement priority has to do with special performance boosts that are based on enforcement priority. This only applies to workloads given the Tactical enforcement priority. In Teradata 13.0 and 13.10, any workload that is given a Tactical enforcement priority will automatically be given an expedited status. This expedited status allows the workload’s queries to make use of special reserved AMP worker tasks pools (if they have been defined), as well as other internal database prioritizations. 

Enforcement priority was so named because at the time of the first TASM release enforcement priority was intended to be used in some future release to play an active part in influencing access to resources. However, with the emergence of Linux SLES 11 and a new priority scheduler for the Teradata Database, enforcement priority has been replaced by some of the new features and capabilities that SLES 11 offers.

So today, think of enforcement priority as primarily documentation, a method of grouping similar workloads for reporting and viewing purposes, with Tactical being the only case of any active, performance-related benefit. In fact many Teradata TASM users simply use the default enforcement priority of Normal for all their non-tactical workloads, so they can more easily move them between allocation groups, as tuning necessitates.

One thing I want to add, before I forget it. When you migrate from Linux SLES 10 to SLES 11, enforcement priority will play a small role in the automatic migration that takes place from the old priority setup to the new priority setup. Once again, this only applies to Tactical workloads. Any workload with a Tactical enforcement priority in SLES 11 will automatically be given a special very high priority positioning within the SLES 11 world.

So the bottom line on enforcement priority is that as long as you get your tactical workloads labeled correctly, it is not going to impact your performance or the balance of your work no matter which enforcement priorities you assign to the other workloads. However, you may find some benefit in the grouping that is done using enforcement priorities when it comes to viewing or filtering your workloads in Viewpoint.