pt-osc spans excessive connections to the replica when executing in the source

--TOTAL_CONNECTIONS in the replica when pt-osc start running
mysql> select users.*,now() from performance_schema.users where user like 'root%';
+------+---------------------+-------------------+---------------------+
| USER | CURRENT_CONNECTIONS | TOTAL_CONNECTIONS | now()               |
+------+---------------------+-------------------+---------------------+
| root |                   2 |              1586 | 2022-02-12 05:29:06 |
+------+---------------------+-------------------+---------------------+
1 row in set (0.00 sec)

--TOTAL_CONNECTIONS in the replica when pt-osc ends
mysql> select users.*,now() from performance_schema.users where user like 'root%';
+------+---------------------+-------------------+---------------------+
| USER | CURRENT_CONNECTIONS | TOTAL_CONNECTIONS | now()               |
+------+---------------------+-------------------+---------------------+
| root |                   2 |              3167 | 2022-02-12 05:33:01 |
+------+---------------------+-------------------+---------------------+
1 row in set (0.00 sec)

# pt-online-schema-change --alter-foreign-keys-method rebuild_constraints --channel $(hostname) --check-interval 60 --chunk-index PRIMARY --chunk-size-limit 255 --chunk-time 0.25 --critical-load Threads_running=1000 --host localhost --max-lag 60 --max-load Threads_running=100 --no-check-alter --no-check-plan --no-check-replication-filters --password verysecretpassword1^ --preserve-triggers --recurse 1 --recursion-method processlist --set-vars wait_timeout=10000 --slave-password verysecretpassword1^ --slave-user root --user root --execute --alter "force" D=dbtest,t=joinit1
Found 1 slaves:
phong-dinh-node4 -> phong-dinh-node4.lxd:socket
Will check slave lag on:
phong-dinh-node4 -> phong-dinh-node4.lxd:socket
Operation, tries, wait:
  analyze_table, 10, 1
  copy_rows, 10, 0.25
  create_triggers, 10, 1
  drop_triggers, 10, 1
  swap_tables, 10, 1
  update_foreign_keys, 10, 1
No foreign keys reference `dbtest`.`joinit1`; ignoring --alter-foreign-keys-method.
Altering `dbtest`.`joinit1`...
Creating new table...
Created new table dbtest._joinit1_new OK.

# administrator command: Quit;
# Time: 2022-02-12T05:24:22.305769Z
# User@Host: root[root] @ phong-dinh-node3.lxd [10.124.33.40] Id: 1588
# Schema: Last_errno: 0 Killed: 0
# Query_time: 0.001378 Lock_time: 0.000052 Rows_sent: 1 Rows_examined: 1184 Rows_affected: 0 Bytes_sent: 211
SET timestamp=1644643462;
SHOW VARIABLES LIKE 'innodb\_lock_wait_timeout';
# Time: 2022-02-12T05:24:22.305928Z
# User@Host: root[root] @ phong-dinh-node3.lxd [10.124.33.40] Id: 1588
# Schema: Last_errno: 0 Killed: 0
# Query_time: 0.000088 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0 Rows_affected: 0 Bytes_sent: 11
SET timestamp=1644643462;
SET SESSION innodb_lock_wait_timeout=1;
# Time: 2022-02-12T05:24:22.307041Z
# User@Host: root[root] @ phong-dinh-node3.lxd [10.124.33.40] Id: 1588
# Schema: Last_errno: 0 Killed: 0
# Query_time: 0.001019 Lock_time: 0.000055 Rows_sent: 1 Rows_examined: 1184 Rows_affected: 0 Bytes_sent: 210
SET timestamp=1644643462;
SHOW VARIABLES LIKE 'lock\_wait_timeout';
# Time: 2022-02-12T05:24:22.307221Z
# User@Host: root[root] @ phong-dinh-node3.lxd [10.124.33.40] Id: 1588
# Schema: Last_errno: 0 Killed: 0
# Query_time: 0.000102 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0 Rows_affected: 0 Bytes_sent: 11
SET timestamp=1644643462;
SET SESSION lock_wait_timeout=60;