I am running Data Loader via command line every night to upsert records from a third party generated CSV (using a Windows Scheduled Task), and am trying to figure out the best way to keep track (in Salesforce) of the last time a record was synched via the Data Loader process. The overall goal is to set up a time trigger to flag records that haven't been updated via Data Loader in 2 days (which means they have been deleted from the third party system), so I can set some fields on the record.
Originally I was thinking about using the LastModifiedDate, but the potential for a user to edit the record would mess that up. From looking at the documentation, I don't see a good way to automatically set a custom field to the current timestamp via Data Loader, but I'm hoping someone else has run into a similar use case.