Problem with aborted PT-online-schema change command
When Percona Online Schema Change runs, it creates triggers which synchronize the new table with updates that happen to the old table (with the previous table definition).

Before you run pt-online-schema change again, you have to delete these triggers.

In MySQL you can find the triggers by writing show triggers like '&lt;table name&gt;'\G.

And you can delete those triggers by typing

drop trigger &lt;trigger name&gt;;

You should only follow this recipe if your table definition does not have other triggers than those created by pt-online-schema change. Their names will start with "pt_osc_".