Bug Report: vreplication and vitess online ddl lose rows_copied on reparent

[olyazavr]

Overview of the Issue

Upon reparent (planned or not), we were seeing a loss of progress in migrations (eg. progress dropping from 90% to 0%). In diving deeper, I noticed that the underlying vreplication stream would continue along, as advertised, and the migration would actually complete, but at < 100% completion reported (however, the percentages before the reparent and after completion would add up to 100%, which pointed me in the right direction).

I found that the rows_copied counter was reset in vreplication upon reparent, but the actual position was kept correct, so this is more of a cosmetic issue, but alarming to see your whole migration drop to 0% on a reparent

Slack conversation

Reproduction Steps

Start a vitess onlineddl migration, wait until it has made some progress, and then reparent. Progress and rows copied will drop to 0, as they will in the underlying vreplication stream. However, the migration will successfully complete, BUT report that it has completed at less than 100% progress and rows_copied will not reach total row count

Binary Version

Vitess 14

Operating System and Environment details

Centos8, Linux 5.4.141-hs22.el8.x86_64

Log Fragments

No response