--attempt-instant-ddl caused process hangs

[NoskyOrg]

gh-ost 1.1.11
aws aurora mysql 8.0.42

when --attempt-instant-ddl succeeds, the process sometimes does not exit. The binlog syncer starts closing, and the last connection is killed, but the gh-ost process remains alive and the MySQL connection stays open until it is manually interrupted.

cmd

./gh-ost --user=root --password='xx' --host=xxx.rds.amazonaws.com --port=3306 \
--database=testdb1 --table=xxx \
--alter="ADD COLUMN id4 INT COMMENT 'a'" \
--assume-master-host=xxx:3306 --default-retries=60 \
--cut-over=atomic --ok-to-drop-table --assume-rbr --allow-on-master \
--max-load=Threads_running=300 --critical-load=Threads_running=3000 \
--chunk-size=2000 --max-lag-millis=2000 \
--skip-metadata-lock-check \
--verbose --execute --attempt-instant-ddl --nice-ratio=0

log

2026-09-21 11:57:09 INFO Applier initiated on ip-xxx:3306, version 8.0.42
2026-09-21 11:57:09 INFO Acquired migration lock gh-ost::testdb1.xxx
2026-09-21 11:57:09 INFO Dropping table `testdb1`.`_xxx_ghc`
2026-09-21 11:57:09 INFO Table dropped
2026-09-21 11:57:09 INFO Creating changelog table `testdb1`.`_xxx_ghc`
2026-09-21 11:57:09 INFO Changelog table created
2026-09-21 11:57:09 INFO Creating ghost table `testdb1`.`_xxx_gho`
2026-09-21 11:57:30 INFO Ghost table created
2026-09-21 11:57:30 INFO Altering ghost table `testdb1`.`_xxx_gho`
2026-09-21 11:57:36 INFO Ghost table altered
2026-09-21 11:57:36 INFO Intercepted changelog state GhostTableMigrated
2026-09-21 11:57:36 INFO Attempting to execute alter with ALGORITHM=INSTANT
2026-09-21 11:57:36 INFO INSTANT DDL query is: ALTER /* gh-ost */ TABLE `testdb1`.`xxx` ADD COLUMN id4 INT COMMENT 'a', ALGORITHM=INSTANT
2026-09-21 11:57:36 INFO Setting LOCK timeout as 6 seconds
2026-09-21 11:57:46 INFO Writing changelog state: Migrated
2026/09/21 11:57:46 INFO syncer is closing...
2026/09/21 11:57:46 INFO kill last connection id=3564340



# I used Ctrl+C to cancel it.
^C