1. problem description:
as the title show, i miss the first problem using pt-online-schema-change tool to modify the table online.
no more message print in the console .
2. sulution:
see the line 8489 of the file 'pt-online-schema-change', you will see code
printf("%s -> %s:%s\n", $cxn->name(), $cxn->{dsn}->{h}, $cxn->{dsn}->{P});copy and annotation,
one by one , test name(), {dsn}, {dsn}->{h}, {dsn}->{P},
you will find that $cxn->{dsn}->{P} is null.
take it away and try again, you will success!