Configuring data movement services options

For every Capture server that is created and configured by the data movement services component, there are two parameters that can affect the behavior of the Capture components. They are the lag_limit and startmodeparameters.

The lag_limit and startmode parameters have the default values: "7 days" and "WARMSI". For more information on these parameters, refer to DB2® SQL Replication Guide and Reference.

You cannot modify these settings until the artifacts are deployed. However, you can alter these settings before you run any of the Capture component servers, or you can change the parameters for currently running Capture servers
Note: To enable changes performed while the Capture servers are running, you need to stop and restart the Capture servers.
If the default settings of the lag_limit and startmode parameters are used while you are deploying replication artifacts, and a Capture server has been stopped for longer than 7 days and then restarted, the Capture component returns an error. The error states that the Capture server cannot run because the data is too old. You can overwrite the default in several ways. The following describes three methods:
  1. Modify the default parameters as specified in the <CAPTURESERVERSCHEMA>.IBMSNAP_CAPPARMS table. After deploying the replication artifacts, you can determine the number of Capture servers that the data movement services component has created by running the following query against the Runtime database.

    CONNECT TO RUNTIME DATABASE

    SELECT DISTINCT OM_NAME, SERVICE_NAME, SRC_RM_CAP_SVR_NAME

    FROM WBIRMADM.RMMETADATA

    ORDER BY 1,2,3

    You see a table like the following:
    Table 1. RMMETADATA example
    OM_NAME SERVICE_NAME SRC_RM_CAP_SVR_NAME
    SubDoctor3 Runtime to Historical CAPTURE_18
    SubDoctor3 State to Runtime CAPTURE_1
    SubDoctor3 State to Runtime CAPTURE_115
    SubDoctor3 State to Runtime CAPTURE_156
    SubDoctor3 State to Runtime CAPTURE_194
    SubDoctor3 State to Runtime CAPTURE_212
    SubDoctor3 State to Runtime CAPTURE_250
    SubDoctor3 State to Runtime CAPTURE_41
    SubDoctor3 State to Runtime CAPTURE_59
    SubDoctor3 State to Runtime CAPTURE_97
    The OM_NAME is the name of the WebSphere® Business Modeler project. The SERVICE_NAME indicates the data movement service, and the SRC_RM_CAP_SVR_NAME is the identifier (CAPTURE SCHEMA) for the Capture server that is being used as part of the data movement service. In the above table, there is one capture server for the Runtime to Historical data movement service and nine for the State to Runtime data movement service.
    Note: The number of servers and the names of the servers vary, based on the model being used and the policy parameters specified during artifact generation.

    The database services component supports all the options for lag_limit and startmode parameters, but you should be aware that there are serious performance problems if the number of cold starts (the start of the Capture servers after failure) increases. If there are frequent cold starts, the ETL component of the data movement service processes all existing records instead of simply recording the changes. Once all of the Capture servers that need to be modified are identified, you can modify the default parameters in the database. Once the default parameters are modified for each Capture server, you can start the Capture servers.

  2. Or modify the command line that starts the Capture server. During generation of the database services artifact, convenience scripts are generated that can start and stop the Capture and Apply servers. The capture start scripts (StartCapture_#.bat or StartCapture_#.sh) are located in the directory <data_movement_service_name>\source. Each of these scripts contains the asncap command, which is used to start the Capture program. For more information about these parameters, refer to IBM® DB2 documentation. Modify the start script accordingly, save, and then run the start script to run the Capture server with the new settings.
  3. Or modify the Capture server during runtime. Follow the instructions found in the IBM DB2 documentation, which describes how to temporarily change the settings for a running Capture server.

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