Pt-archiver --stop and --unstop options for idempotence

Hello,

I was wondering if there is a way to stop and restart a pt-archiver command with a specific WHERE clause, ensuring that the tool restarts exactly from the point where it was stopped, guaranteeing idempotence and avoiding archiving rows that have been already migrated.

I tried to use the options --stop and --unstop, but I did not manage to achieve this goal, since at the restart the tool was trying to archive data already migrated (giving the error duplicate entry for primary key).
Maybe I’m missing something concerning this options, or there is some other way to achieve idempotence?

Thank you in advance,
Giulio.