Description:
If we do any select on installed plugin, a consequent uninstall will get deferred with a warning:
+--------------+
| version() |
+--------------+
| 5.1.28-debug |
+--------------+
1 row in set (0.00 sec)
mysql> use test;
Database changed
mysql> show plugins;
+------------+--------+----------------+---------+---------+
| Name | Status | Type | Library | License |
+------------+--------+----------------+---------+---------+
| binlog | ACTIVE | STORAGE ENGINE | NULL | GPL |
| CSV | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MEMORY | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MRG_MYISAM | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MyISAM | ACTIVE | STORAGE ENGINE | NULL | GPL |
+------------+--------+----------------+---------+---------+
5 rows in set (0.00 sec)
mysql> INSTALL PLUGIN INNODB SONAME 'ha_innodb.so';
Query OK, 0 rows affected (1.48 sec)
mysql> show plugins;
+------------+--------+----------------+--------------+---------+
| Name | Status | Type | Library | License |
+------------+--------+----------------+--------------+---------+
| binlog | ACTIVE | STORAGE ENGINE | NULL | GPL |
| CSV | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MEMORY | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MRG_MYISAM | ACTIVE | STORAGE ENGINE | NULL | GPL |
| MyISAM | ACTIVE | STORAGE ENGINE | NULL | GPL |
| InnoDB | ACTIVE | STORAGE ENGINE | ha_innodb.so | GPL |
+------------+--------+----------------+--------------+---------+
6 rows in set (0.00 sec)
mysql> create table t1 (id int primary key) engine=innodb;
Query OK, 0 rows affected (0.01 sec)
mysql> select * from t1;
Empty set (0.00 sec)
mysql> uninstall plugin innodb;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> show warnings;
+---------+------+----------------------------------------------------+
| Level | Code | Message |
+---------+------+----------------------------------------------------+
| Warning | 0 | Plugin is busy and will be uninstalled on shutdown |
+---------+------+----------------------------------------------------+
1 row in set (0.01 sec)
How to repeat:
See above
Suggested fix:
The warning 'Plugin is busy...' comes from sql_plugin.cc
1718 if (plugin->ref_count)
1719 push_warning(thd, MYSQL_ERROR::WARN_LEVEL_WARN, 0,
1720 "Plugin is busy and will be uninstalled on shutdown");
1721 else
1722 reap_needed= true;
1723 reap_plugins();
The ref_count is non-zero because a SELECT results in incrementing it thrice but decrementing it twice. I cannot fathom the need for incrementing ref_count multiple times for the same select but this asymmetry of increment/decrement is causing the delay in uninstall.
The increments to ref_count happen in open_binary_frm() in table.cc.
