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Status Not under consideration
Workspace Db2 for z/OS
Created by Guest
Created on Mar 30, 2016

RELATED IDEAS

Lock hashing algorithms of DB2 and XES are incompatible. Leads to excessive False Contention and high IRLM CPU for GLM xfer

There is an anomaly between DB2 and XES hashing algorithms which means that a 4-byte DB2 (unique) lock hash value passed to XES may not be hashed to a unique value by XES unless the LTE size is set excessively high (1G).

I understand that DB2 hashing value takes in to account DBID, OBID, Page Number, Row id, so high False Contention is likely when multiple update processes run in a Datasharing environment against the same Table.

Global Lock Manager (GLM) ownership transfer occurs on Commit for locks which are hashed uniquely in DB2, but to the same hash value in XES (and therefore subject to False Contention). This can lead to very high volumes of XCF signalling and IRLM (SRB) CPU spikes on Commit of a large UOW in a DB2 Datasharing environment. With IRLM running at SYSSTC priority, this will have a major impact on a running system.

The suggestion is that DB2 and XES hashing algorithms should be made more compatible so that the probability of uniqueness in XES is increased and False Contention is reduced (at reasonable LTE size). DB2 performance is improved.
  • Admin
    Janet Figone
    Reply
    |     Apr 25, 2021

    Thank you for submitting this enhancement request. While we view all the enhancement requests we receive as valuable and we would like to implement all of them, in an effort to have maximum transparency we are closing the ones that don’t currently appear on our two year product roadmap. This is not to say that these enhancements may not still be implemented at some point in the future as we do evaluate our requirements on the basis of customer demand and technical impact, to deliver maximum value to our customers.


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


    Sincerely,

    The Db2 for z/OS Team

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