In IBM DB2 for z/OS, the REORG TABLESPACE command has an option called SHRLEVEL CHANGE which allows you to change the sharing level of a table space while the table space is being reorganized. The sharing level determines how the table space is shared among different DB2 subsystems.

 

The two main sharing levels are:

 SHRLEVEL REFERENCE: This sharing level allows multiple DB2 subsystems to access the same table space, but each subsystem has its own copy of the data. This means that changes made to the data by one subsystem are not visible to the other subsystems until the table space is reorganized.

 

 SHRLEVEL CHANGE: This sharing level allows multiple DB2 subsystems to access the same table space, and changes made to the data by one subsystem are immediately visible to the other subsystems.

 

When you use the SHRLEVEL CHANGE option during a REORG TABLESPACE command, the table space is reorganized and the sharing level is changed at the same time.

 

For example, the following command can be used to change the sharing level of a table space called "MYTABLESPACE" to SHRLEVEL CHANGE while the table space is being reorganized:

REORG TABLESPACE MYTABLESPACE SHRLEVEL CHANGE

It's important to note that changing the sharing level of a table space can have an impact on the performance of the database and it's important to test the performance of the table space

SHRLEVEL REFERENCE is a sharing level that allows multiple DB2 subsystems to access the same table space, but each subsystem has its own copy of the data. This means that changes made to the data by one subsystem are not visible to the other subsystems until the table space is reorganized.

 

When you use the SHRLEVEL REFERENCE option during a REORG TABLESPACE command, the table space is reorganized and the sharing level is changed at the same time.

 

For example, the following command can be used to change the sharing level of a table space called "MYTABLESPACE" to SHRLEVEL REFERENCE while the table space is being reorganized:

REORG TABLESPACE MYTABLESPACE SHRLEVEL REFERENCE

It's important to note that changing the sharing level of a table space can have an impact on the performance of the database and it's important to test the performance of the table space after the change to ensure that it meets the desired requirements.

 

Also, SHRLEVEL REFERENCE is useful when you want to isolate different subsystems and prevent them from seeing each other's changes. This can be useful in a development or testing environment where different teams are working on different tasks and need to work independently.