This topic applies only to the IBM Business Process Manager Standard configuration.

This topic applies only to the IBM Business Process Manager Advanced configuration.

Maintaining change logs on federated IBM BPM systems

The change log is a transaction log on an IBM® BPM system that consumers can examine to monitor and discover changed task-related data on the system.

About this task

A consumer is the indexing service on Process Federation Server for a specific IBM BPM system. The consumer indexes the changed data and marks the task in the change log as consumed.

The change log table includes a row for each monitored task instance, and a column for each Process Federation Server consumer. The rows and columns indicate the consumption status for task instances and consumers. When an indexing service starts, it automatically reserves a consumer column in the change log table. Consumers are identified by their ibmPfs_federatedSystem IDs.

By default, the change log table includes 20 columns that can support up to 20 consumers. Only the first 5 columns are indexed. If you have more than 5 consumers, you can improve performance by creating a database table index for each additional column that you use. See the create_bpd_change_log.ddl script for examples of the table indexes that you can create.

If your federated environment has more than 20 consumers, you can add columns to the table. You can also clear column reservations if they are no longer needed by their consumers.

Procedure

The following steps show SQL statements for an IBM BPM BPD system. For BPEL systems, replace BPD in the statements with BPEL.

Add consumer columns to the change log.
1. Add a new column to the table by using an SQL statement similar to the following example, which shows how to add the 21st column to the table.
```
ALTER TABLE PFS_BPD_CHANGE_LOG ADD CONSUMER_021 DECIMAL(5,0) DEFAULT 0 NOT NULL
```
2. Add the name of the new column from the previous step to the consumer change log by using an SQL statement similar to the following example:
```
INSERT INTO PFS_BPD_CHANGE_LOG_CONSUMER (COLUMN_NAME) VALUES ('CONSUMER_021')
```
Clear column reservations. If a consumer's ibmPfs_federatedSystem ID changes or if a consumer is no longer needed, you can reclaim the reserved columns. Clear column reservations only if all the existing columns are reserved and you do not want to add new columns to the table.
1. Shut the consumer down.
2. Clear the column name registration by using an SQL statement similar to the following example, which shows how to clear the reservation for the 20th column.
```
UPDATE PFS_BPD_CHANGE_LOG_CONSUMER SET CONSUMER_ID = NULL WHERE COLUMN_NAME = 'CONSUMER_020'
```
3. Reset the state of the consumer column by using an SQL statement similar to the following example. The example shows how to reset the 20th column.
```
UPDATE PFS_BPD_CHANGE_LOG SET CONSUMER_020 = 0
```