Chat now with support
Chat with Support

SQL Optimizer for DB2 LUW 4.4.1 - User Guide

SQL Optimizer for IBM® DB2® LUW
UsageStatistics Getting Started Options SQL Scanner SQL Optimizer SQL Formatter SQL Inspector Database Explorer SQL Repository Index Impact Analyzer Index Usage Analyzer User-Defined Temp Table Editor Functions SQL Functions SQL Information and Functions Activity Log
Tutorials About us Copyright

Plan Statistics Page

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.

Summary Page

ClosedView the Summary tab

The Summary tab in the SQL Optimizer window displays the Run Time information and the cost estimates from various perspectives.

Run Time Pane

The Run Time pane displays the run time statistics for retrieving all records and for retrieving the first record.

Cost Estimates

Cost statistics shown on the Summary tab are estimated cumulative costs across all operations used in the access plan.

Item

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.

Charts

The statistics from the grid are grouped together and displayed in charts.

To select how many records are displayed in the charts

Select the number from the Number of Alternatives list.

To select which statistic to use to select the records

Select the statistic from the By list.

To select the top or the bottom range of the statistic

Select Asc (Ascending) or Desc (Descending) from the Order option.

Display or Hide Panes

Use the pane-control buttons to reorganize the panes:

To display the statistics and charts

Click Chart and Statistics .

To display only the charts 

Click Chart Only.

To display only the statistics

Click Statistics Only .

 

Compare Page

ClosedView the Compare Tab

The Compare tab in the SQL Optimizer window enables you easily to compare SQL text, access plans, and statistics between two alternatives or between an alternative and the original SQL.

The Compare tab consists of two major panes—Source of Comparison and Compare With. Each pane shows information for one alternative. Differences in syntax and access plans are highlighted in either pane.

Display or Hide Panes

Use the pane-control buttons to reorganize the panes:

To display panes vertically

Click image\B_Rotate.gif.

To display panes horizontally

Click image\B_Rotate.gif.

To display or remove SQL Text panes

Click .

To display or remove Access Plan panes

Click .

To display or remove Statistics panes

Click .

 

Execute Result Page

The Execution Result tab in the SQL Optimizer window compares the data returned by the original SQL with the data returned by any one of the SQL alternatives.

To compare all rows of data between the original SQL and an SQL alternative

  1. Select Unlimited for Max rows to compare.
  2. From the SQL list, select the SQL alternative that you want to compare with the original SQL.
  3. Click .

To compare a limited number of rows between the original SQL and an alternative

  1. Enter the number of rows in Max rows to compare.
  2. From the SQL list, select the SQL alternative that you want to compare with the original SQL.
  3. Click .

Comparison Grid

The grid in the top pane provides quick overview of returned-data differences. The numbers of returned columns and rows show whether the SQL alternative produces the same result as the original SQL statement. The displayed time shows how long it took to execute Batch Run or the Run Time, not the time it took to retrieve the data for the Execution Result tab.

Note: If the Data statistic shows that the returned data differs when you retrieve limited rows, do not assume that the alternative is returning wrong data. The difference can suggest that the alternative has returned data in an order different from the order returned by the original SQL. Two SQL statement are considered to be semantically equivalent if they retrieve the same data in any order (as long as the ORDER BY clause is not used in the SQL statement).

Comparison Functions

To refresh the data for the currently selected alternative

Click .

To clear all the data for original and all alternatives

Click .

To abort Compare SQL or Refresh SQL process

Click .

 

Related Documents