The following post present the process and the steps using simple demo and clear explanation:
Please correct me if I am wrong
the status of the checkpoint file
DATA UNDER CONSTRUCTION - Means this file is open for inserting new rows
ACTIVE - The rows from UNDER CONSTRUCTION will put into files in ACTIVE checkpoint files .
MERGE_TARGET - Initially these checkpoint file are empty, until manually issue CHECKPOINT, and the rows from current ACTIVE checkpoint files will be insert to this MERGE_TARGET, and than mark ACTIVE .
WAITING FOR LOG TRUNCATION - Means these files can be truncate (or delete/ or reuse ) after doing log backup ? I am quick confuse on this type checkpoint files.