XISCAN node

This operation is performed for a single query predicate.

Node name: XISCAN

Represents: Its evaluation narrows down the qualifying return set of rows IDs and XML node IDs by range scanning any associated index over XML data before accessing the base table. The use of an index can improve the performance of a query because the compiler determines whether and how to use index information to complete the query. This typically results in:
  • The sorting of nodes by document and the elimination of any duplicates.
  • The fetching of each row of the table that contains the qualifying documents.
  • An XSCAN operation on the XML document.
Performance suggestions:
  • Over time, database updates might cause an index to become fragmented, resulting in more index pages than necessary. This can be corrected by dropping and recreating the index, or reorganizing the index.
  • When two or more tables are being accessed, access to the inner table by means of an index can be made more efficient by providing an index on the join column of the outer table.
  • If statistics are not current, update them using the RUNSTATS command.

Feedback