PM77236: UNEXPECTED TABLESPACE GROWTH DURING UPDATE'S WHEN ROW-LEVEL-LOCKING & SMALL MAXROWS VALUE

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APAR status

  • Closed as program error.

Error description

  • Tablespaces may not be using available space on a page for
    UPDATE's, causing unexpected tablespace growth.
    .
    This growth problem may occur when all of the following occur:
    .
     1) Row-Level-Locking is in affect.
     2) Multiple units-of-work are updating the same page at the
        same time.  Some change must be affected holes (shrinking
        or deleting a row).
     3) The page already has MAXROWS number of rows on it.
    .
    When space is being looked for on a page, but another update
    is already in progress on the same page that affect holes, by
    either changing a row to be smaller or deleting a row, then
    the holes on that page cannot be used at this point.
    The contiguous freespace at the end of the page, if any,
    might be able to be used.
    .
    The current code, at the point described above, checks the
    number of rows, to see if it is already at the MAXROWS value,
    and if it is, then other pages are then checked for space.
    This logic is correct, if the operation is an INSERT, but not
    correct for an UPDATE, as it would not be adding a new row, and
    the existing space on the page could have been used.
    

Local fix

  • Increase the MAXROWS value.
    Change to Page-Level-Locking.
    Avoid updates to same pages, if possible.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED: DB2 9 and 10 for z/OS users of tablespaces   *
    *                 with MAXROWS attributes under RRL - row      *
    *                 level locking.                               *
    ****************************************************************
    * PROBLEM DESCRIPTION: Unexpected Growth of tablespaces        *
    *                      under massive concurrent delete and     *
    *                      update operations.                      *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    Under the following circumstances, the tablespace can grow:
     (1) The tablespace is defined without hash organization.
     (2) Row-Level-Locking is in affect
     (3) Multiple units-of-work are updating the same page
         at the same time and the total RIDs already reached the
         MAXROWS.
     (4) The page has reached the MAXROWS limit, but the page
         has contiguous free space to hold updated row size.
    Today, DB2 code verifies the MAXROWS limit first and eliminates
    the need to use contiguous free space within the page during
    the UPDATE operation which creates a bigger size of row.
    As a result, the updated row was processed as an overflow
    record which is then inserted to other data pages and caused
    more data pages to be created.
    

Problem conclusion

  • DB2 code is modified to ignore the MAXROWS checking for UPDATE
    operation which allows the UPDATE to use the contiguous free
    space if it is adequate.
    

Temporary fix

  • *********
    * HIPER *
    *********
    

Comments

APAR Information

  • APAR number

    PM77236

  • Reported component name

    DB2 OS/390 & Z/

  • Reported component ID

    5740XYR00

  • Reported release

    A10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-11-16

  • Closed date

    2013-01-03

  • Last modified date

    2013-04-02

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

    UK90725 UK90726

Modules/Macros

  •    DSNIREPR DSNISGRT DSNISMRT
    

Fix information

  • Fixed component name

    DB2 OS/390 & Z/

  • Fixed component ID

    5740XYR00

Applicable component levels

  • RA10 PSY UK90725

       UP13/01/19 P F301

  • R910 PSY UK90726

       UP13/01/19 P F301

Fix is available

  • Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.



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Document information


More support for:

DB2 for z/OS

Software version:

A10

Reference #:

PM77236

Modified date:

2013-04-02

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