mysql Enable automatic rehashing方式登陆hang问题

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登陆myql数据库的crmdb schema一直hang：

# mysql -uroot -proot_beehive -Dcrmdb
Warning: Using a password on the command line interface can be insecure.
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

查询进程：

# mysql -uroot -proot_beehive
.......

mysql> show processlist;
+------+------+---------------------+--------------------+------------+------+---------------------------------+------------------------------------------------------------------------------------------------------+-----------+---------------+
| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined |
+------+------+---------------------+--------------------+------------+------+---------------------------------+------------------------------------------------------------------------------------------------------+-----------+---------------+
| 8073 | root | localhost | crmdb | Query | 4284 | Sending data | create table offer_2_party_bk2 as select a.offer_id,a.atom_action_id,a.party_id,a.start_dt,a.end_dt, | 0 | 0 |
| 8075 | root | localhost | mysql | Sleep | 487 | | NULL | 0 | 0 |
| 8079 | root | localhost | crmdb | Field List | 2775 | Waiting for table metadata lock | | 0 | 0 |
| 8082 | crm | 132.228.47.137:3947 | information_schema | Sleep | 1698 | | NULL | 0 | 0 |
| 8084 | root | localhost | crmdb | Field List | 274 | Waiting for table metadata lock | | 0 | 0 |
| 8085 | root | localhost | NULL | Query | 0 | init | show processlist | 0 | 0 |
+------+------+---------------------+--------------------+------------+------+---------------------------------+------------------------------------------------------------------------------------------------------+-----------+---------------+

看到一个元数据锁等待，执行一个field list的命令。

在上面hang之前提示使用-A 选项登陆mysql：

[root@bssmysqlcsdb02 ~]# mysql --help
mysql Ver 14.14 Distrib 5.6.19-67.0, for Linux (x86_64) using EditLine wrapper
Copyright (c) 2009-2014 Percona LLC and/or its affiliates
Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Usage: mysql [OPTIONS] [database]
-?, --help Display this help and exit.
-I, --help Synonym for -?
--auto-rehash Enable automatic rehashing. One doesn't need to use
'rehash' to get table and field completion, but startup
and reconnecting may take a longer time. Disable with
--disable-auto-rehash.
(Defaults to on; use --skip-auto-rehash to disable.)
-A, --no-auto-rehash
No automatic rehashing. One has to use 'rehash' to get
table and field completion. This gives a quicker start of
mysql and disables rehashing on reconnect.

automatic rehashing实际上相当于tab键的提示，默认情况下，加-Dcrmdb会加载元数据，提供tab提示：

# mysql -uroot -proot_beehive -Dcrmdb --auto-rehash

......

mysql> select offer_ --按tab键

-------------------------------------------------------------提示
offer_id offer_member.bill_start_dt offer_member.end_dt offer_member.offer_member_id offer_member.status_dt
offer_member offer_member.bss_end_dt offer_member.member_id offer_member.offer_role_id offer_member.version
offer_member.atom_action_id offer_member.bss_start_dt offer_member.obj_type offer_member.start_dt offer_member_id
offer_member.bill_end_dt offer_member.create_dt offer_member.offer_id offer_member.status_cd offer_role_id

这就是所谓的automatic rehashing

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