错误Threads_running=58 exceeds its critical threshold 50
#pt-online-schema-change --user=root --password= e835 --alter='ENGINE=InnoDB' --socket=/data/db/mysql6980/mysql6980.sock --execute D='discuz_db',t='pre_forum_post'
1> Cannot connect to S=/data/db/mysql6980/mysql6980.sock,h=172.106.301.52,p=...,u=root
1> Cannot connect to S=/data/db/mysql6980/mysql6980.sock,h=172.106.301.53,p=...,u=root
1> Cannot connect to S=/data/db/mysql6980/mysql6980.sock,h=172.106.301.54,p=...,u=root
No slaves found. See --recursion-method if host ca444egi-b44-mys44ql02 has slaves.
Not checking slave lag because no slaves were found and --check-slave-lag was not specified.
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
Altering `discuz_db`.`pre_forum_post`...
Creating new table...
Created new table discuz_db._pre_forum_post_new OK.
Altering new table...
Altered `discuz_db`.`_pre_forum_post_new` OK.
2019-04-24T09:14:44 Creating triggers...
2019-04-24T09:14:44 Created triggers OK.
2019-04-24T09:14:44 Copying approximately 17085984 rows...
2019-04-24T09:14:59 Dropping triggers...
2019-04-24T09:14:59 Dropped triggers OK.
2019-04-24T09:14:59 Dropping new table...
2019-04-24T09:14:59 Dropped new table OK.
`discuz_db`.`pre_forum_post` was not altered.
2019-04-24T09:14:59 Error copying rows from `discuz_db`.`pre_forum_post` to `discuz_db`.`_pre_forum_post_new`: Threads_running=58 exceeds its critical threshold 50
解决办法：
添加： "--critical-load Threads_running=100"项