DB2 10.5 for Linux, UNIX, and Windows

XSCAN operator

This operator is used to navigate XML fragments to evaluate XPath expressions and to extract document fragments if needed.

Operator name: XSCAN

Represents: This operator processes node references passed by a nested-loop join operator (NLJOIN). It is not represented with a direct input in the access plan.

For example, consider the following XQuery statement:

XQUERY for $i in db2-fn:xmlcolumn("MOVIES.XMLCOL")//actor return $i

The access plan for this statement as provided by the db2exfmt utility shows an XSCAN operator processing document node references retrieved by a table scan on the table TELIAZ.MOVIES. The XSCAN operator in this case returns actor node references found within the TELIAZ.MOVIES.XMLCOL collection.

          Rows 
         RETURN 
         (   1) 
          Cost 
           I/O 
           |
           180 
         NLJOIN 
         (   2) 
         10137.9 
          1261 
          /-+\
       180      1 
     TBSCAN  XSCAN  
     (   3)  (   4) 
     21.931   56.2 
        1       7 
       |
       180 
 TABLE: TELIAZ   
     MOVIES