Optimizing memory consumption for a Classic data server (guidelines)

To optimize memory consumption, estimate initial memory settings in the job control language (JCL) for your Classic data server and then evaluate them in a test environment.

Procedure

  1. Estimate initial values for REGION in the JCL for the Classic data server and for the MESSAGEPOOLSIZE configuration parameter.
    • For smaller environments, try the default values for the Classic data server:
      • REGION=96MB
      • MESSAGEPOOLSIZE=64MB
    • Consider larger values for REGION and MESSAGEPOOLSIZE for larger deployments that require more resources. For example, you can begin with values that are larger than needed at first. Then you can define your environment and work toward reducing these values by monitoring the environment and running reports such as the output from the DISPLAY,MEMORY command.

      Consider factors that contribute to resource consumption:

      • Fixed overhead per Classic data server outside message pool storage:
        • C runtime library functions (LE)
        • Added threads, such the log reader thread that reads logs for the replication log stream for each subscription.
      • The number of subscriptions, and related metadata:
        • Subscriptions
        • Replication mappings
        • Replication objects
  2. Experiment with different configurations in a test environment to verify that your Classic data server has sufficient resources for the size of your environment.
    1. Specify a region size that is at least 8 MB lower than the site limit, and use the greater of these values:
      • 8 MB higher than the message pool
      • 20% higher than the message pool
      If the 8 MB gap between the region and the message pool is still not sufficient, increase this difference in increments of 8 MB.
    2. Set the MESSAGEPOOLSIZE parameter to the greater of these values:
      • 20% less than the region size
      • 8 MB below the REGION value or 8 MB below any site limit imposed by exits.

      If you increase the value of the MESSAGEPOOLSIZE parameter, set the region size higher to maintain the 8 MB gap.

  3. If possible, set the maximum cache size of 3 GB per subscription for the source and target server.

    Caches on the source and target server use storage areas outside of the message pool storage, but those storage areas can also be a factor in estimating region size.