mysql> use dbl Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A
登录时出现这种情况，一般是有大量库，表，字段需要扫描，会很慢，登录库时可以加上-A参数不进行预读，速度会很快。
参考http://dba.stackexchange.com/questions/62102/mysql-database-freezing-after-use/62103
On the first "use" command after login, MySQL scans database, tables and columns name for auto completion. If you have many db, tables it could take a while.
To avoid that, launch your client with the -A option (or --no-auto-rehash)
mysql>mysql -uroot -p -A</CODE>
You could also add the disable_auto_rehash variable in your my.cnf (in the [mysql] section) if you want to disable it completely. This change does not require a reboot (it is a client, not server, variable).