Client datasets use different mechanisms for incorporating changes from the change log, depending on whether the client datasets stores its data in a file or represents data obtained through a provider. Whichever mechanism is used, the change log is automatically emptied when all updates have been incorporated. 

File-based applications can simply merge the changes into the local cache represented by the Data property. They do not need to worry about resolving local edits with changes made by other users. To merge the change log into the Data property, call the MergeChangeLog method. Merging changes into data describes this process. 

You can't use MergeChangeLog if you are using the client dataset to cache updates or to represent the data from an external provider component. The information in the change log is required for resolving updated records with the data stored in the database (or source dataset). Instead, you call ApplyUpdates, which attempts to write the modifications to the database server or source dataset, and updates the Data property only when the modifications have been successfully committed. See Applying updates for more information about this process.