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Status Delivered
Workspace Db2 for z/OS
Created by Guest
Created on Jun 9, 2020

RELATED IDEAS

Choose statement concentration in JDBC on a per-statement level

See this idea on ideas.ibm.com

Statement concentration is a good thing if you have software that is not well written and uses literals where it should use parameter markers.

However, there are cases where using a literal helps the optimizer make a better decision. Statement concentration, on the JDBC connection level, is all-or-nothing.

I had a recent case where a query used a LIKE predicate. Using a literal, Db2 chose index access and the query ran fast; with a parameter marker, it chose a TS scan. So, I told the developer to not use a parameter marker in his program but dynamically construct the SQL and use a literal instead. However, statement concentration is turned on in the JDBC data source so this did not help.

Needed by Date Jun 9, 2020
  • Guest
    Reply
    |     Aug 25, 2020

    Right, the CONCENTRATE STATEMENTS attribute does exist for the PREPARE statement and it does exactly what I need. Problem being, in JDBC we cannot use PREPARE directly; it's the driver that does it for us.

    That said, I found later that a Db2 specific API does in fact allow turning statement concentration on or off dynamically (the setDBStatementConcentrator API as documented here: https://www.ibm.com/support/knowledgecenter/SSEPEK_12.0.0/java/src/tpc/imjcc_r0021824.html). It does affect only statements that are being prepared after it is executed; so we need to perform four steps:

    1. Remember the old setting for statement concentration

    2. Turn statement concentration on

    3. Prepare the statement

    4. Reset the statement concentration setting to its old value

    It would be more elegant to be able to do this on a single prepareStatement call, but one can live with it.

  • Admin
    Janet Figone
    Reply
    |     Aug 24, 2020

    We are pleased to inform you that this request was delivered in a previously released version of the product by using a prepare CONCENTRATE STATEMENTS attribute.

    Sincerely,

    Db2 for z/OS Development

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