The system property "org.jbpm.correlationkey.length" was added as part of the JIRA -
RHPAM-1569 (https://issues.jboss.org/browse/RHPAM-1569) and it controls the size of the collaboration key that is stored in RHPAM database. By default, the size is set to 255 meaning that only first 255 characters of the correlation key will be stored in the "name" column in the CorrelationKeyInfo table as well in the "correlationKey" column in the ProcessInstanceLog table.
The same correlation key will be stored in the "value" column in the CorrleationPropertyInfo but the number of characters stored in the "value" column is not controlled with the above system property. That means, that we'll have the same error if we try to add correlation key longer then what is defined in the database schema (255 by default).