Special Considerations for DQL Language Queries › Estimated Statistics

Estimated Statistics

The Option Table parameter, MAXIO, allows a site to specify an I/O threshold giving a number of estimated I/Os. When this number is exceeded by the number of I/Os estimated to process a DQL FIND statement, the following new panel will be displayed. The user has the option to continue <PF4> CONTINUE or not <PF2> RETURN. The I/O threshold may be set for an individual user using the online User Table Maintenance. The user's threshold value if any would take precedence over the System Option Table value. The Estimated Statistics panel is displayed after optimization but before retrieving any data.

Estimated Statistics (DQMI0)

 =>
 Estimated statistics have exceeded maximum limits.  To proceed with query:
 press the PF4 key.  To cancel execution of query; press the PF2 key.
 ------------------------------------------------------------------------DQMI0
 DATAQUERY:  ESTIMATED STATISTICS                  QUERY NAME: DEMOJOIN
 -----------------------------------------------------------------------------

              NUMBER REQUESTED: ALL


      FIND TERMINATED BECAUSE:  TOTAL ESTIMATED I/O EXCEEDS ESTIMATED MAX I/O

                                ESTIMATED
                                ---------
      TOTAL ESTIMATED ROWS:          24
      TOTAL JOINS EXAMINED:           2
      VALID JOINS EXAMINED:           2
      TOTAL ESTIMATED I/O            26     **



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 <PF1> HELP     <PF2>  RETURN      <PF3> NOT USED    <PF4> CONTINUE

Action

To continue and retrieve the rows, press <PF4> CONTINUE.

To stop, press <PF2> RETURN or <CLEAR>.

Panel Description

TOTAL ESTIMATED ROWS

Number of rows to be retrieved by the FIND.

TOTAL JOINS EXAMINED

Number of possible ways to join tables named in FIND.

VALID JOINS EXAMINED

Number of valid joins.

TOTAL ESTIMATED I/O

Estimated I/O to execute FIND - based on the lowest cost join.