About rowcount

Hi,

./gh-ost --host=10.10.193.99 --user=root --password= --database=test --table=test_tab --alter="drop columns" --chunk-size=2000 --exact-rowcount --max-load=Threads_connected=100 --allow-on-master --assume-master-host=10.10.193.99 -assume-rbr --initially-drop-ghost-table --execute

Copy: 6066000/6078350 99.8%; Applied: 976; Backlog: 1/1000; Time: 9m54s(total), 9m54s(copy); streamer: mysql-bin.000354:142247281; State: migrating; ETA: 1s
Copy: 6076000/6078350 100.0%; Applied: 978; Backlog: 0/1000; Time: 9m55s(total), 9m55s(copy); streamer: mysql-bin.000354:145120989; State: migrating; ETA: 0s
Copy: 6078209/6078209 100.0%; Applied: 978; Backlog: 0/1000; Time: 9m55s(total), 9m55s(copy); streamer: mysql-bin.000354:145694651; State: migrating; ETA: due
Migrating `iudp_zt_policy`.`policy`; Ghost table is `iudp_zt_policy`.`_policy_gho`
Migrating i-b1nk89p8:3306; inspecting i-b1nk89p8:3306; executing on dlidcdbcopy2.aeonlife.com.cn
Migration started at Thu Dec 26 15:23:13 +0800 2019
chunk-size: 2000; max-lag-millis: 1500ms; dml-batch-size: 10; max-load: Threads_connected=100; critical-load: ; nice-ratio: 0.000000
throttle-additional-flag-file: /tmp/gh-ost.throttle
Serving on unix socket: /tmp/gh-ost.iudp_zt_policy.policy.sock
Copy: 6078209/6078209 100.0%; Applied: 978; Backlog: 0/1000; Time: 9m56s(total), 9m55s(copy); streamer: mysql-bin.000354:146059231; State: migrating; ETA: due

Why the last rowcount 6078209 less than 6078350 ? I think the last rowcount will be the maximum number.

Thanks.