Lower High Water Mark

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Against automatically-managed tablespaces, this action lets you build and submit an ALTER TABLESPACE... REDUCE statement, specifying that existing containers be reduced by a specified size.

Against database-managed tablespaces, you build and submit an ALTER TABLESPACE... LOWER HIGH WATER MARK statement followed by an ALTER TABLESPACE... REDUCE statement, explicitly lowering the high water mark before reducing the size of the tablespace.

Note: Before using this object action, consult DB2 LUW documentation for information on automatic and non-automatic storage, storage reclaimasbility, as well as database versus system-managed tablespaces. For more information, see Accessing Third Party Documentation.

Platform Availability

To Lower the High Water Mark for a Tablespace

  1. Initiate a Lower High Water Mark action against a tablespace. For more information see Initiating an object operation.
  2. Use the following table as a guide to understanding and choosing options in the Lower High Water Mark dialog:
Pane Options

Action Options

Against automatically-managed tablespaces, this pane lets you provide the REDUCE option value for the generated ALTER TABLESPACE statement. Two options are provided. Selecting MAX specifies that the high water mark be lowered by moving the maximum number of extents to the beginning of the tablespace. Specifying a Size and Unit specifies the numeric value by which the tablespace is to be reduced through extent movement. Against database-managed tablespaces, this pane only allows you to specify that All Containers are to be decreased by a specified Size (in Pages, KB, MB, or GB Units). If you want to specify individual containers, use the Containers panel.


This tab is only available for database-managed tablespaces. As well, the functionality provided depends on whether you selected the All Containers option on the Action Options pane. With All Containers selected, this panel lets you specify an ON DBPRATITIONNUM clause on the ALTER TABLESPACE... REDUCE statement generated, specifying partitions for the container operations. Click the Partitions button, select one or more partitions on the Select Partitions dialog, and click OK. With All Containers deselected, this panel lets you specify an ON DBPRATITIONNUM clause and also lets you specify a database container clause on the ALTER TABLESPACE... REDUCE statement generated. For each container to be included in the databae container clause, click the Add Container button, select a container from the dropdown, and select a Size and Unit (Pages, KB, MB, or GB) for the container.


Displays the DDL generated to execute the operation. For more information, see Preview.

3. Execute or Schedule the action.