IBM Support

IC81916: A prefetch request at a high offset into a large tablespace may lead to a hang situation.

Subscribe

You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • Under certain conditions tablespace I/O will be done by db2
    prefetcher edus.
    When very large tablespaces exist and an I/O request is
    submitted to a db2 prefetcher
    that is at an offset higher than  2^31 x <the DB2 I/O size>,
    then the request submitting edu may hang and the I/O request
    never completes.
    This can cause the application or eventually even the database
    to hang.
    
    A typical stack trace would show :
    
    sqloCSemP
    sqlbpfParallelDirectIO
    sqlbpfParallelDirectRead
    ...
    
    Note that this stacks trace is typical for any edu waiting for
    an I/O to be done by the prefetchers,
    but the stack should not remain the same indefinitely.
    
    This problem is more likely to occur on LOB I/O, when the I/O
    size is only 1k.
    So any I/O request above 2^31 x 1k = 2TB could cause a hang in
    this case.
    

Local fix

  • Disable the parallel I/O for the tablespace where your object is
    located.
    
    For example, if the object is in tablespace 3 use the following
    registery:
    db2set DB2_PARALLEL_IO=3:1
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * All                                                          *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * Under certain conditions tablespace I/O will be done by db2  *
    * prefetcher edus.                                             *
    * When very large tablespaces exist and an I/O request is      *
    * submitted to a db2 prefetcher                                *
    * that is at an offset higher than  2^31 x <the DB2 I/O size>, *
    *                                                              *
    * then the request submitting edu may hang and the I/O request *
    * never completes.                                             *
    * This can cause the application or eventually even the        *
    * database to hang.                                            *
    *                                                              *
    * A typical stack trace would show :                           *
    *                                                              *
    * sqloCSemP                                                    *
    * sqlbpfParallelDirectIO                                       *
    * sqlbpfParallelDirectRead                                     *
    * ...                                                          *
    *                                                              *
    * Note that this stacks trace is typical for any edu waiting   *
    * for an I/O to be done by the prefetchers,                    *
    * but the stack should not remain the same indefinitely.       *
    *                                                              *
    * This problem is more likely to occur on LOB I/O, when the    *
    * I/O size is only 1k.                                         *
    * So any I/O request above 2^31 x 1k = 2TB could cause a hang  *
    * in this case.                                                *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to V9.7 FP7 or disable the parallel IO               *
    ****************************************************************
    

Problem conclusion

  • First fixed in V9.7 FP7
    

Temporary fix

Comments

APAR Information

  • APAR number

    IC81916

  • Reported component name

    DB2 FOR LUW

  • Reported component ID

    DB2FORLUW

  • Reported release

    970

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-03-08

  • Closed date

    2012-06-05

  • Last modified date

    2012-06-05

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

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

    IC84529 IT03579

Fix information

  • Fixed component name

    DB2 FOR LUW

  • Fixed component ID

    DB2FORLUW

Applicable component levels

  • R910 PSY

       UP

  • R950 PSY

       UP

  • R970 PSY

       UP

  • R980 PSY

       UP



Document information

More support for: DB2 for Linux, UNIX and Windows

Software version: 9.7

Reference #: IC81916

Modified date: 05 June 2012