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SQL Optimizer for DB2 LUW 4.4.1 - User Guide

SQL Optimizer for IBM® DB2® LUW
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Access Plan Page

Quest SQL Optimizer for IBM® DB2® LUW maximizes SQL performance by automating the manual, time-intensive and uncertain process of ensuring that SQL statements are performing as fast as possible. SQL Optimizer analyzes, rewrites, and evaluates SQL statements within multiple database objects, files, or SQL statements captured by the DB2 Event Monitor. With SQL Optimizer, you can analyze and optimize all your problem SQL from multiple sources. SQL Optimizer also provides you a complete index optimization and plan change analysis solution, from index recommendations to simulated index impact analysis, through comparison of multiple SQL access plans.

SQL Optimizer provides you with the following main modules.

SQL Optimizer (including SQL Rewrite and Generate Indexes functions)

SQL Formatter

Database Explorer

SQL Scanner

SQL Inspector

SQL Repository

Index Impact Analyzer

Index Usage Analyzer

 

Access Plan Page

ClosedView the Access Plan tab

 

The Access Plan tab in the SQL Optimizer window uses the following panes to display access plan details for the currently selected alternative and information about the objects that the alternative syntax accesses:

Access Plan

Object Statistics

Index Statistics

Column Statistics

Column Values Distribution Statistics

Regenerate Virtual Index Sets

You can rerun the Generate Indexes function to obtain the latest index recommendations.

Note: This process will clear all existing SQL and index-set alternative in this SQL Optimizer session.

To regenerate virtual index sets

Right-click within any of the statistics panes, and select Recommend Virtual Indexes.

Create Your Own Virtual Index Sets

You can add your own index sets to this SQL Optimizer session.

To create your own virtual index sets

Right-click within any of the statistics panes, and select Create Virtual Indexes.

Display or Hide Panes

Use the pane-control buttons to reorganize the panes.

To display the Access Plan, and the Table, Index, Column, and Column Value Distribution panes

Click .

To display only the Access Plan pane

Click .

 

Access Plan

ClosedView the Access Plan pane

The access plan is a combination of steps the DB2 LUW database optimizer chooses to execute a SQL statement. Each node represents how the database optimizer will physically retrieve rows of data from the database or how the data is prepared. By examining the access plan, you can see exactly how the database executes your SQL statement.

Right-click Menu

The Access Plan pane contains a right-click menu that allows you to perform the following functions:

Function

Description

Print

Sends the access plan in its current view to the printer, to display on the screen (print preview), or to a file.

Copy

Copies the access plan to the clipboard.

View Plan

Changes how the access plan is displayed.

Animated Plan Steps

Highlights one-by-one the access plan steps.

Plan Options

Opens the Access Plan Options window so you can select the specific detailed information that is displayed in the access plan. You can also choose to display specific information in individual columns.

Get Help on plan_step

Displays the help text for the currently selected step in the access plan.

Help on Access Plan

Opens online help for the access plan.

 

Related Topics

Table Statistics Pane

ClosedView the Object Statistics pane

The Object Statistics pane is displayed on the Access Plan tab in the SQL Optimizer window. It lists information for each table, view, or alias referenced in the access plan. If the operation in the selected access plan step accesses a specific object, this object is automatically highlighted in the Table Statistics pane. You can do the following in this pane:

  • Select an object in this pane to view statistics about its indexes and columns (in the Index and Column Statistics panes, respectively).

  • Right-click a specific object to update its catalog statistics.

ClosedAppend mode

The method in which rows are inserted on pages in the table or view:

Value

Description

Rows appended

New rows are inserted at the end of the data.

Rows inserted

New rows are inserted into existing spaces if available.

ClosedCheck count

The number of check constraints defined on the table or view.

This information is based on the CHECKCOUNT value for the table or view in SYSCAT.TABLES.

ClosedCol count

The number of columns in the table or view.

This information is based on the COLCOUNT value for the table or view in SYSCAT.TABLES.

ClosedFile pages

Total number of pages allocated for this table.

This information is based on the FPAGES value for the table or view in SYSCAT.TABLES.

ClosedIndex tablespace

The name of the tablespace that holds all the indexes created for the table or view.

This information is based on the INDEX_TBSPACE value for the table or view in SYSCAT.TABLES.

ClosedKey columns

The number of columns that make up the primary key for the table or view.

This information is based on the KEYCOLUMNS value for the table or view in SYSCAT.TABLES.

ClosedKey unique

The number of unique constraints (other than a primary key constraint) defined for the table or view.

This information is based on the KEYUNIQUE value for the table or view in SYSCAT.TABLES.

ClosedLOB tablespace

The name of the tablespace that holds all long data (for LONG or LOB column types) for the table or view.

This information is based on the LONG_TBSPACE value for the table or view in SYSCAT.TABLES.

ClosedLock size

The preferred lock granularity when DML statements are executed on the table:

Value

Description

Row

Row-level lock

Lock

Table-level lock

blank

Not applicable

ClosedObject name

The qualified name of the table or view.

This information is based on the TABSCHEMA and TABNAME values for the table or view in SYSCAT.TABLES.

ClosedOverflow

Total number of overflow records in the table or view. An overflow record is an updated record that is too large to fit on the page in which it is currently stored. The record is copied to another page, and its original location is replaced with a pointer to the new page.

This information is based on the OVERFLOW value for the table or view in SYSCAT.TABLES.

ClosedPages

Total number of pages that contain data for the table or view.

This information is based on the NPAGES value for the table or view in SYSCAT.TABLES.

ClosedPct free

Percentage of each page in the table or view to be reserved for future inserts.

This information is based on the PCTFREE value for the table or view in SYSCAT.TABLES.

ClosedPart mode

The mode used to distribute data in the table or view within a partitioned database:

Value

Description

Hash on partition key

Hash on the partitioning key

Replicate across partitions

Replicate table or view data across partitions

blank

No partitioning. The table, view, or alias exists in a single partition nodegroup with no partitioning key defined. A blank also appears for nicknames.

ClosedRI children

The number of referential constraints in which the table or view is a parent (that is, the number of dependent tables of this table).

This information is based on the CHILDREN value for the table or view in SYSCAT.TABLES.

ClosedRI parents

The number of referential constraints in which the table or view is a dependent (that is, the number of parent tables of this table).

This information is based on the PARENTS value for the table or view in SYSCAT.TABLES.

ClosedRI self

The number of referential constraints in which the table or view is both a parent and a dependent.

This information is based on the SELFREFS value for the table or view in SYSCAT.TABLES.

ClosedRows

Total number of data rows in the table or view.

This information is based on the CARD value for the table or view in SYSCAT.TABLES.

ClosedStatistics time

The timestamp for the last time a change was made to statistics for the table or view.

This information is based on the STATS_TIME value for the table or view in SYSCAT.TABLES.

ClosedStatus

Status type for the object from which information is retrieved:

Value

Description

Normal

Normal status for the table, view, alias, or nickname.

Check

CHECK PENDING status on the table or nickname. Constraint checking is turned off, and SELECT, INSERT, UPDATE, and DELETE operations are not allowed on the table.

X

Inoperative view or nickname. This status can occur when the underlying tables of the view or nickname have been dropped.

ClosedTablespace

The name of the primary tablespace for the table or view.

This information is based on the TBSPACE value for the table or view in SYSCAT.TABLES.

ClosedType

The type of table or view from which information is retrieved:

Value

Description

Table

Normal table

Hierarchy

The hierarchy table associated with the implementation of a typed table hierarchy

Summary

Summary table

View

Normal view

Alias

An indirect reference to a table

Nickname

A reference to a table (data source) in a federated database

Typed table

Table created from a structured type

Type view

A view created from a structured type

ClosedVolatile

The indicator showing whether the table or view has been declared volatile. A volatile table is a table whose contents vary greatly--from empty to large--at any point in time. To generate the access plan for a volatile table, DB2's SQL optimizer tends not to rely on existing table statistics and, therefore, often uses an index scan instead of a table scan. Values for this detail include:

Value

Description

Cardinality of table is volatile

Table is volatile

blank

Table is not volatile

 

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