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:
- 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
exampleOM_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.
- 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.
- 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.