You have control over the number and size of journal data sets. Journal data sets must be large enough so that they do not fill too often during the day; however, they must also be small enough so that the contents of a full journal can be saved in a reasonable length of time before the other journals also fill up.
You set the number of journal data sets with the ACBS parameter of the DB macro. You can define from 2 to 255 journal data sets to this parameter.
TIBCO Object Service Broker Application Administion for information on how to make changes to journal data set sizes, including re-allocating and re-initializing journal data sets.