Additional synchronizations have been put into place to prevent two checkpoints from overlapping ensuring complete serialization of the checkpoint process. If the checkpoint was forced from an application level CTCHKPNT() call, and an in-process checkpoint is already in progress, the call returns NO_ERROR and the sysiocod is set to OCHK_COD (-885). This avoids any additional processing overhead as a checkpoint is already in progress.
A server configuration option is available to disable the check on in-progress checkpoints so they can overlap as previously allowed.
COMPATIBILITY CHECKPOINT_OVERLAP