PM47428: POOR PERFORMANCE RESULTS IF THE RESULT OF A PATH EXPRESSION IN XSLT OR XQUERY CONTAINS MANY NODES FROM TEMPORARY TREES

APAR status

• Closed as program error.

Error description

• If the result of evaluating a path expression in XSLT or
  XQuery is a sequence of nodes, the nodes must be sorted in
  document order.  When it evaluates a path expression whose
  result is a sequence of nodes that were constructed by the XSLT
  stylesheet or XQuery expression itself, the processor is
  failing to recognize cases in which the nodes are already
  in document order, and always sorts them.
  
  If such a path expression returns a very large number of
  constructed nodes, the performance impact for the XSLT
  stylesheet or XQuery expression can be significant.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:  All IBM WebSphere Application Server        *
  *                  Feature                                     *
  *                  Pack for XML users                          *
  ****************************************************************
  * PROBLEM DESCRIPTION: In evaluating a step expression in an   *
  *                      XSLT stylesheet or XQuery expression,   *
  *                      the processor is required to ensure     *
  *                      that the result of the step             *
  *                      expression consists of nodes sorted     *
  *                      in document order, with duplicates      *
  *                      eliminated.  If the result of           *
  *                      evaluating such an expression           *
  *                      contains nodes that were constructed    *
  *                      by the stylesheet or expression         *
  *                      itself, the processor fails to          *
  *                      recognize many situations in which      *
  *                      the sequence of nodes is already in     *
  *                      document order with no duplicates,      *
  *                      and sorts the sequence.  This results   *
  *                      in poor performance.                    *
  ****************************************************************
  * RECOMMENDATION:  Install a fix pack that contains this       *
  *                  APAR.                                       *
  ****************************************************************
  The processor evaluates a step expression in an XSLT
  stylesheet or XQuery expression by iterating through the nodes
  returned by evaluating the expression on the left-hand side of
  the "/" operator, and for each, evaluating the expression on
  the right-hand side of the operator.  All the results of
  evaluating the right-hand side are concatenated into a single
  sequence, and if not already known to be sorted in document
  order, the sequence of nodes is sorted into document order
  with duplicates eliminated.  If that sequence consists of
  nodes that were constructed by the XSLT stylesheet or XQuery
  expression, the processor is sorting the nodes even if the
  nodes are already in document order.
  

Problem conclusion

• The problem was resolved by having the processor check when it
  concatenates sequences of nodes that result from evaluating a
  step expression, whether every pair of adjacent sequences is
  already known to be sorted in document order with no
  duplicates, and if so, whether the last node in each such
  sequence comes before the first node in the immediately
  following sequence.  If both of those conditions hold, the
  processor marks the sequence that results from concatenating
  those individual sequences as being known to be already sorted
  in document order with no duplicates, and hence, no further
  expensive sorting operation is required.
  
  The fix for this APAR is currently targeted for inclusion in
  fix pack 1.0.0.11.  Please refer to the Recommended Updates
  page for delivery information:
  http://www.ibm.com/support/docview.wss?rs=180&uid=swg27004980
  

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:

  PM47656

Fix information

• Fixed component name

  XML FEATUREPACK

• Fixed component ID

  5724J0856

Applicable component levels

• R700 PSY

     UP