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SQL Optimizer for DB2 LUW 4.4.1 - Installation Guide

Plan Statistics Tab

The Plan Statistics tab in the SQL Optimizer window displays the cost for each step in the access plan for the currently selected SQL or index-set alternative, along with the plan's arguments and values, its predicates, and the columns involved in the data stream.

Cost Statistics Pane

The Cost Statistics pane provides detailed descriptions of each operation used in the access plan.

Estimated Cost Statistics

The following statistics are shown for each row of the access plan:

Statistic Description
Buffers The estimated cumulative number of logical read requests for data pages that have gone through the buffer pool. This value is expressed in 4KB page units.
Communication The estimated cumulative communication cost of executing the access plan up to and including the operation specified in the selected step. This value is expressed in TCP/IP frame units.
CPU The estimated cumulative number of CPU instructions required to execute the access plan up to and including the operation specified in the selected step.
First row The estimated cumulative cost of fetching the first row of data for the access plan up to and including the operation specified in the selected step. This statistic is expressed in timeron units.
First row comm. The estimated cumulative communication cost of fetching the first row of data for the plan up to and including the operation specified in the selected step. This statistic is expressed in TCP/IP frame units.
I/O The estimated total number of I/Os required for the access plan, up to and including the operation specified in the selected step. This value is expressed in units of 4KB pages.
Next row CPU The estimated cumulative number of CPU instructions required to fetch the second row of data for the plan up to and including the operation specified in the selected step.
Next row I/O The estimated cumulative number of I/Os required to fetch the second row of data for the plan up to and including the operation specified in the selected step. This statistic is expressed in timeron units.
Next row total The estimated cumulative cost of fetching the second row of data up to and including the operation specified in the selected step. This statistic is expressed in timeron units.
Object name The name of the table, view, or alias involved in the operation.
Operation A brief description of the operation performed on the data, as specified in the selected access plan step.
Remote comm. The estimated cumulative communication cost of executing the remote access plan up to and including this operator. This statistic is expressed in TCP/IP frame units.
Remote total The estimated cumulative cost of performing operations on a remote database for this access plan up to and including the operation specified in the selected step. This statistic is expressed in timeron units.
Step The number of the step within the sequence of steps performed in the access plan.
Total cost The estimated cumulative cost of executing the access plan up to and including the operation specified in the selected step. This statistic is expressed in timeron units.

To see the Argument, Predicate, and Column information for a specific step

  1. Select a specific plan step in the Cost Statistics pane.
  2. Click the Argument, Predicate, or Column tab.

Argument

The Arguments tab lists the arguments and their values that are used in the access plan operation highlighted in the Statistic pane.

Predicate

The Predicates tab provides information about the SQL predicates that the operation highlighted in the Statistic pane is processing.

The following information shows for each predicate:

Columns

The Columns tab lists the table columns involved in the data stream for the access plan operation highlighted in the Cost Statistics pane.

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