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The Compression Status screen provides information about tables that are already compressed, or that are candidates for compression.

The following tab pages are available on the Compression Status screen:

Compressed Tables

Displays all tables that are already compressed

Compression Candidates

Displays all tables where space could be saved by using compression Note

As of DB2 V9.7, index compression is available and supported by the DBA Cockpit. End of the note.

Compressed Tables

On this tab page, all tables meeting at least one of the following requirements are displayed: The table is enabled for data compression and contains compressed records. The indexes of a table are enabled for index compression and are compressed.

Column Description

Table Schema Name of the table schema

Table Name Name of the table

Data

Compression If the table is enabled for data compression, this checkbox is selected. Index

Compression

If the index of the selected table is enabled for index compression, this checkbox is selected.

Savings (MB)

Total savings of space

This includes all savings regardless, whether they are caused by data or index compression

Total Size

Total size of the table

The value displayed is the sum of DATA, LONG, LOB, XML, and index pages over all database partitions,

Savings (%) Percentage of savings

Column Description Last Check Time Last check time

Compression Candidates

On this tab page, tables that meet at least one of the following requirements are displayed: A table has already been compressed but more space could be saved by

recompressing it based on a better compression dictionary.

A table has been enabled for data compression but still contains compressed records that are not yet compressed.

A table whose indexes are not yet enabled for index compression

A table whose indexes are compressed but more space could be saved by recompressing the table

Column Description

Table Schema Name of the table schema

Table Name Name of the table

Data Compression If row compression is enabled, this option is selected.

Index

Compression If index compression is enabled, this option is selected.

Estimated Savings (MB)

Total savings of space that can be achieved

This includes all savings regardless, whether they are caused by data or index compression.

If the table has already been compressed, then the value displayed does not represent the new total savings but the additional savings.

Total Size Total size of table if the compression would be performed

Estimated Savings

(%) Percentage of estimated (additional) savings Last Check Date Last check date

Displaying Details About the Compression Status of a Table

You can display details about the compression status of a table by choosing a line in the overview table.

Note

The compression results are based on checks that have been performed before in the background. These checks evaluate statistics data that was gathered by the RUNSTATS utility. In case of missing or incomplete statistics data, the calculated check results can be inaccurate. In this case, an appropriate message is displayed. To display more details, choose Show more details. You are redirected to the Single Table Analysis screen where you can do further analysis.

For more information, see Analyzing and Maintaining a Single Table [page 154]. End of the note.

The following information is displayed in the Compression Status Details detail area:

Field Description

Summary

Schema Name Name of database schema

Table Name Name of the table

Total Size Total size in KB of the table (including indexes)

Total Table Size Total size in KB of the table

Total Index Size Total size in KB of the index

Data Compression If this checkbox is selected, data in this table is compressed

Index Compression If this checkbox is selected, the index of this table is compressed

Current Savings

Total Total amount of savings in KB for this table (including indexes)

Total Compression Ratio Total compression ratio in percent for this table

Data Total amount of savings in KB for the data of this table

Data Compression Ratio Total compression ratio in percent for the data of this table

Index Compression Ratio Total compression ratio in percent for all indexes of this

table

Estimated Savings

Total Total amount of estimated savings in KB of this table

(including indexes)

Total Compression Ratio Estimated total compression ratio in percent

Data Amount of estimated savings of data in KB

Data Compression Ratio Estimated data compression ratio in percent

Index Amount of estimated savings in KB for all indexes

Index Compression Ratio Estimated index compression ration

Additional Savings after Compression

Total amount of savings in KB if the table would be compressed again

Check Date Date when table was last checked

Check Time Time when table was last checked

Scheduling a Compression Job

To implement the estimated space savings, the affected tables need to be reorganized as follows:

1. On the Compression Candidates tab page, select all tables that you want to compress and choose the Compress pushbutton.

2. In the Schedule Job dialog box, you specify when you want the compression job to run:

o To run the job immediately, choose the Start Immediately in the Background radio button.

o To schedule the job at a certain day and time, choose the Schedule radio button and specify an appropriate date and time.

3. To schedule the compression job, choose OK.

The appropriate REORG jobs are scheduled in the DBA Planning Calendar where you can view the progress of the compression job.

Note

Depending on the required actions to perform the compression, there can be separate REORG jobs for table and for indexes.

Refreshing the Compression Status

Since compression information is not collected by the data collection framework (DCF) on a regular basis because of performance reasons, you must run compression checks manually as follows:

1. On the Compression Status screen, choose the Start Compression Check… pushbutton.

2. In the Schedule Compression Check dialog box, you specify when you want the compression check job to run:

o To run the job immediately, choose the Start Immediately in the Background radio button.

o To schedule the job at a certain day and time, choose the Schedule radio button and specify an appropriate date and time.

3. To schedule the compression job, choose OK.

A job is scheduled in the DB2 administrative task scheduler (ATS).

You can view view the progress of the compression check job either under Jobs

Scheduled DB Tasks or in the DBA Planning Calendar where you choose DB

Collectors from the Category dropdown list.