What are the pros and cons of using a large global subschema versus a smaller tailored subschema?

Document ID : KB000044523
Last Modified Date : 14/02/2018
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Question: 

We use one global subschema for every ADS dialog and COBOL program.

What are the pros and cons of using a large global subschema versus a smaller tailored subschema?

 

Answer: 

Global subschemas are easier to maintain but require more storage space. Tailored subschemas require more work to maintain but need less storage space. 

The size of the subschema affects the following: 

  • Subschema control blocks IB50 and VB50
  • Currency block ($*$CURCY)
  • ADS FDB Subschema Area Name Table (SSAN). 
  • Ready Area Table (RAT). If the dialog does a READY ALL which is the default, all areas will be readied.  

The larger the subschema the more ADS storage is allocated per task and the more database storage is allocated per run-unit. 

To prevent resource contention and poor performance it is always best to use a tailored subschema rather than one big global subschema.