Class XPLAINDefaultVisitor

java.lang.Object
org.apache.derby.impl.sql.execute.xplain.XPLAINDefaultVisitor
All Implemented Interfaces:
XPLAINVisitor
public class XPLAINDefaultVisitor extends Object implements XPLAINVisitor
This is the Default Visitor which produces explain information like the old getRuntimeStatistics() approach.
It exists to support backward-compatibility. The only thing this visitor does, is to log the output of the statistics to the default log stream. (the file derby.log)

  • Constructor Details

    • XPLAINDefaultVisitor

      public XPLAINDefaultVisitor()

  • Method Details

    • visit

      public void visit(ResultSetStatistics statistics)
      Description copied from interface: XPLAINVisitor
      This is the Visitor hook method, which gets called from each ResultSetStatistics. It depends on the sub-class implementation of this interface, to describe the behaviour of the explanation facility.
      To be easily extendable with new explain representation methods, just implement this interface and provide the new behaviour.
      Specified by:
      visit in interface XPLAINVisitor
      Parameters:
      statistics - the statistics, which want to get explained.

    • reset

      public void reset()
      Description copied from interface: XPLAINVisitor
      Call this method to reset the visitor for a new run over the statistics. A default implementation should call this method automatically at first of a call of doXPLAIN().
      Specified by:
      reset in interface XPLAINVisitor

    • doXPLAIN

      public void doXPLAIN(RunTimeStatistics rss, Activation activation)
      Description copied from interface: XPLAINVisitor
      This method is the hook method which is called from the TopResultSet. It starts the explanation of the current ResultSetStatistics tree and keeps the information during one explain run.
      Specified by:
      doXPLAIN in interface XPLAINVisitor

    • setNumberOfChildren

      public void setNumberOfChildren(int noChildren)
      Description copied from interface: XPLAINVisitor
      This method informs the visitor about the number of children. It has to be called first! by the different explainable nodes before the visit method of the visitor gets called. Each node knows how many children he has. The visitor can use this information to resolve the relationship of the current explained node to above nodes. Due to the top-down, pre-order, depth-first traversal of the tree, this information can directly be exploited.
      Specified by:
      setNumberOfChildren in interface XPLAINVisitor
      Parameters:
      noChildren - the number of children of the current explained node.