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Status Not under consideration
Workspace Db2 for z/OS
Created by Guest
Created on Jul 25, 2019

Improve persistent thread concurrency

With the implementation of transactions with persistent threads (like pseudo wait-for-input on IMS) we have been facing some concurrency issues in our site, specially with HPU and batch programs that perform lock escalation. This happens because the persistent thread claims an intent lock on the table/partition and, since our plans have the parameter RELEASE set to DEALLOCATE, never releases it. Programs that try to claim non-intent locks on the table/partition used by persistent threads get a timeout.

Previously the concurrency issues were worse because no utility could run against tables that were acessed by persistent threads, but the problem was solved with the introduction of the PKGREL_COMMIT parameter on v11.

To solve the concurrency issues, we propose a similar behavior as introduced by the PKGREL_COMMIT parameter: dynamically changing the RELEASE parameter (from DEALLOCATE to COMMIT) when a process claims a non-intent lock on the table/partition used by the persistent thread.

 

Itau-Unibanco S.A.

  • Admin
    Janet Figone
    Reply
    |
    Nov 30, 2022

    Thank you Joshua. I have asked Db2 development to review your comment and provide feedback.

  • Guest
    Reply
    |
    Nov 30, 2022

    There are three fundamental ways in which concurrent execution can improve performance: to reduce latency (that is, to make a unit of work execute faster); to hide latency (that is, to allow the system to continue doing work during a long latency operation); or to increase through put .

    The main way we can avoid such concurrency issues and build reliable code is to work with immutable objects. This is because their state cannot be modified by the interference of multiple threads. However, we can't always work with immutable objects.

  • Admin
    Janet Figone
    Reply
    |
    Dec 10, 2020

    Thank you for submitting this Db2 for z/OS enhancement request.

    After giving the request a comprehensive review, we have determined that we cannot include it as a candidate in an upcoming product deliverable because the request has a high implementation cost with a low relative value. As a consequence we will not be implementing this request.

    We appreciate your input to the Db2 for z/OS development team. We also hope that you will continue to submit ideas for improvements as customer feedback is a key component to shaping the future direction of Db2 for z/OS.

    Sincerely,

    Db2 for z/OS Team

  • Admin
    Janet Figone
    Reply
    |
    Oct 16, 2020

    Hello, Yes. The additional input you provided has been shared with the Db2 for z/OS developer reviewing this idea. We will let you know if any additional information is needed. Thank you.

  • Guest
    Reply
    |
    Aug 14, 2020

    Hello, Janet.

    Did you see our last update on November 21, 2019 ?

    Is it enough to allow analysis proceed or do you need/want more information ?

    IDEA is NEED MORE INFORMATION.

    Could you let us know, please ?

  • Guest
    Reply
    |
    Nov 21, 2019

    Hello, Janet.

    Here is a scenario:
    Transaction 1 updates records in the table A. Since transaction 1 is in a PWFI (pseudo wait-for-input) IMS region (the program will never be deallocated) and its plan is bound with the release parameter set to "deallocate", an IX (intent exclusive) lock will be constantly held on the table A. Then, the batch program 2 tries to scan table A with read stability, but since it claims many READ row locks it will try to escalate its locks to a table shared lock. This will cause program 2 to receive a timeout or deadlock message, since the shared lock will never be obtained on table A because of the release parameter on the transaction 1. The same would happen when running a HPU with LOCK YES on table A.

    We would like to know if it is possible to change the behaviour of the release parameter to dynamically change to "COMMIT" on a plan whenever a non-intent lock is requested on an object that has locks held by it. That way, program 2 would claim a shared lock on table A and the release parameter on transaction 1 would dynamically change to "COMMIT", allowing it to release the locks held on table A on the next commit.

  • Admin
    Janet Figone
    Reply
    |
    Nov 21, 2019

    Thank you for submitting this Idea. We have reviewed it and would like to ask if you can please send in a detailed scenario, perhaps with messages, or anything providing more details. Thank you.