Output adapters use the truncate window to inform the log window of which data has been processed by the adapter and can be safely deleted.
It has three columns, simpleKey (integer), gdKey (long), and purge (boolean). The simpleKey column is currently just a dummy value of 0 or 1, and its sole purpose is to serve as a key for the truncate window. The gdKey column contains the value of the gdKey that the output adapter has successfully processed. The log window uses this to delete all the data that has a gdKey equal to or lesser than the provided value. In the purge column, a value of true indicates that the data in the log window needs to be deleted. The output adapter updates this column.
Assign this window to a log store to ensure data recovery from this window in the case of a failure.