JR26737: SQL0901N ON QUERY RUN.

DB2 Version 9.1 Fix Pack 4a for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 4 for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 7  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 5   for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 6   for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 6a for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 7a  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 8  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 9  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 10  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 11  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 12  for Linux, UNIX and Windows

APAR status

• Closed as program error.

Error description

• SQL0901N on query run.
  

Local fix

• n/a
  

Problem summary

• This problem creates a cyclic corelation QGM because
  correlated columns could not map to the new destination box
  properly. To illustrate the problem, let's consider the QGM
  below:
  
  
                  ____  S_____
   uaQunp  |                     | pdQunp
         standing              push down
           UA                    UA
         /    \                   /    \
        S1    S2              S     S correlated to uaQunp
  
  After push down,
  
                 S
   uaQunp  |
           standing
             UA
           /    \
        S1    S2
          \_____\
                 |
                push down
                  UA
                /    \
               S     S  <-- still correlated to uaQunp
                            The correlation should have been moved
  down
                            to the quns under S1 and S2 but as
                            the push down UA is a CSE at this
  stage
                            it could not resolve to new column
  until
                            the CSE is broken off later.
  
  The strategy is to swap the standing UA and push down UA. That
  will automatically resolve the correlation issue.
  
  Bob has fixed a similar problem in defect 370298. In that
  problem, the correlation in push down UA is to a table
  joins to the standing UA (table BT). Bob has fixed the problem
  by reordering the push down sequence. He called
  sqlnr_sort_sips_order to order the quns according to correlation
  dependency. The dependent of the correlation
  will push down first (in this case, the correlated push down UA)
  before the parent of the correlation (table BT.)
  Bob's work does not solve the problem found in this defect. In
  addition, Bob's work creates a new problem.
  
  The quantifiers collected to do the join push down is done
  sqlnr_test_join_predicate in two passes. The first half of the
  quantifier array (BTqunpset, renamed to joinQunpList in v9) ,
  collected in the first pass, contains the quantifiers of
  direct joins to standing UA. The second half contains the
  quantifiers of indirect joins. By reordering the quantifiers
  in Bob's work, it may happen that an indirect join attempts to
  push down to standing UA. This push down attempt
  will fail because there is no join between the indirect join qun
  and the standing UA. It requires the 'link table' that joins
  directly to the standing UA to push down first.
  
  The fix in this defect does the following
  1. In sqlnr_test_join_predicate, move push down UA to the front
  of BTqunpset (or joinQunpList in v9) array in the first pass
  2. In sqlnr_joinppd_magic_detail (or sqlnr_joinppd_rewrite in
  v9), remove the call to sqlnr_sort_sips_order
  3. In sqlnr_joinppd_rewrite, reverse the walk of joinQunpList
  from end-to-beginning back to from beginning-to-end
  4. In sqlnr_joinppd_rewrite, add checking that if push down UA
  is correlated to standing UA, swap the UA in the next attempt of
  joinppd
  

Problem conclusion

• This was fixed in  FP4.
  

Temporary fix

Comments

APAR Information

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

  JR26735

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

  JR27774

Fix information

• Fixed component name

  DB2 UDB WSE WIN

• Fixed component ID

  5765F3501

Applicable component levels

• R910 PSY

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