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Status Not under consideration
Workspace Db2 for z/OS
Created by Guest
Created on Apr 1, 2021

RELATED IDEAS

Improving latch contention in Db2 z/OS

DB2 workloads run at a priority that is related to their origin (may it be batch, IMS, DDF, …) and according to WLM service class definitions.

In high system utilization scenarios, or due to workloads running in a WLM service class with a resource group maximum, it may well happen for a service class to be assigned to a very low priority, or even tasks may be marked non dispatchable in order to keep service class’ CPU utilization below the maximum defined to their resource group.

If a task can't have access to the CPU due to its low priority and it's holding a latch, even for a few seconds (2-5), contention may happen and undesired side effects could arise, as we’ve often observed in our OLTP.

Current contention notification seems too “slow” in trying to solve such situations, and there’s a noticeable negative impact to our highly response time sensitive online workload.

Blocked workload support has solved the problem to some extent, as we’re still facing latch contention episodes (even though we’ve set the BLWLINTHD to its minimum allowed value of 1) and this solution seems inelegant to us (we’re promoting all CPU blocked tasks, may they be holding latches or not, may they be high or low priority workloads…)

Needed by Date Dec 31, 2021
  • Admin
    Janet Figone
    Reply
    |     Aug 24, 2021

    Dear Carlos, My sincerest apologies but the enhancement development is planning to implement is not going to solve the problem of 2-5 second latch waits. You will need to rely upon the system to ensure each task gets its fair share of CPU, but ultimately if the system remains severely constrained in terms of CPU then latch waits are an inevitable consequence. Therefore, unfortunately, we will be closing this idea as Not under consideration.

    Sincerely,

    The Db2 for z/OS Development team

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