IC70004: INSERTING INTO TABLE WITH SMALL EXTENT SIZE AND UNCOMMITTED FREESPACE IS SLOW

APAR status

• Closed as program error.

Error description

• If the next extent size of a table is configured to small for
  the amount
  of data inserted, IDS will repeatedly double the extent size if
  too many
  extents are created. But if the new extents can be created by
  enlarging
  the current extent, there is no threat of overflowing the extent
  table
  and no extent doubling is done.
  
  But in this case a big performance problem can occur if the
  table
  has a lot of free space that belongs to not yet committed
  deletes. Every
  time before the current extent is enlarged, the whole table is
  scanned
  for usable free space. Pages with free space have to be brought
  into the
  buffer pool and the lock manager has to be consulted to see if
  the free
  space on the page belongs to an open transaction.
  
  These are the symptoms:
  
    - Insert performance becomes very low
      (below one row per second in some cases).
  
    - Stack traces of the running insert mostly contain
  
         allocvrow
  
    - If there are multiple inserting threads, there are lots of
  bufwaits
      for bitmap pages
  
         bf_bfwait
         buffget
         allocvrow
  
  The onstat -pt output will not show the problem directly:
  
      TBLspace Report for d:user1.t1
          ...
  
          Pagesize (k)                   2
          First extent size              8
          Next extent size               8
          Number of pages allocated      22112
          Number of pages used           22112
          ...
  
          Extents
               Logical Page     Physical Page        Size Physical
  Pages
                          0         1:1504541        1672
  1672
                       1672         1:1509276       20440
  20440
  
  But a second look reveals that both extents above have been
  enlarged
  far beyond the specified next extent size of 8k.
  
  Workaround:
  
    Make sure the extent size is specified adequately.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All users                                                    *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * Inserts will be slow when small extents are used and there   *
  * is uncommitted free space in previous extents.               *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to IDS.11.50.xC8                                     *
  ****************************************************************
  

Problem conclusion

• The extent allocation was adjusted to double in an appropriate
  way.
  

Temporary fix

Comments

APAR Information

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

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

Fix information

• Fixed component name

  IBM IDS ENTRP E

• Fixed component ID

  5724L2304

Applicable component levels

• RB15 PSN

     UP

• RB15 PSY

     UP