简介
TokuDB使用LockTree(ft-index/locktree)来维护事务的锁状态(row-lock和range-lock)，LockTree的数据结构是一个Binary Tree。
本篇将通过几个“栗子”来谈谈TokuDB的row-lock和range-lock。
表t:
mysql> show create table t\G
*************************** 1. row ***************************
Table: t
Create Table: CREATE TABLE `t` (
`id` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=TokuDB DEFAULT CHARSET=latin1
row-lock
mysql> set autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into t values (1),(10),(100);
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from information_schema.tokudb_locks\G
*************************** 1. row ***************************
locks_trx_id: 238
locks_mysql_thread_id: 3
locks_dname: ./test/t-main
locks_key_left: 0001000000
locks_key_right: 0001000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
*************************** 2. row ***************************
locks_trx_id: 238
locks_mysql_thread_id: 3
locks_dname: ./test/t-main
locks_key_left: 000a000000
locks_key_right: 000a000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
*************************** 3. row ***************************
locks_trx_id: 238
locks_mysql_thread_id: 3
locks_dname: ./test/t-main
locks_key_left: 0064000000
locks_key_right: 0064000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
3 rows in set (0.00 sec)
从tokudb_locks表可以查询到，生成了3条row-lock(locks_key_left和locks_key_right相等)。
为了存储和显示方便，locks_key_left/locks_key_right取key的hash值。
range-lock
mysql> set autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql> delete from t where id<100;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from information_schema.tokudb_locks\G
*************************** 1. row ***************************
locks_trx_id: 280
locks_mysql_thread_id: 12
locks_dname: ./test/t-main
locks_key_left: -infinity
locks_key_right: ff64000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
1 row in set (0.00 sec)
从tokudb_locks表可以查询到，where条件的rang-lock区间为[-infinity, ff64000000]，只要其他事务的锁区间跟这个有任何重叠，则需要等待。
锁冲突
client1执行如下操作:
mysql1> set autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql1> insert into t values (1),(10),(100);
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql1> select * from information_schema.tokudb_locks\G
*************************** 1. row ***************************
locks_trx_id: 283
locks_mysql_thread_id: 14
locks_dname: ./test/t-main
locks_key_left: 0001000000
locks_key_right: 0001000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
*************************** 2. row ***************************
locks_trx_id: 283
locks_mysql_thread_id: 14
locks_dname: ./test/t-main
locks_key_left: 000a000000
locks_key_right: 000a000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
*************************** 3. row ***************************
locks_trx_id: 283
locks_mysql_thread_id: 14
locks_dname: ./test/t-main
locks_key_left: 0064000000
locks_key_right: 0064000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
3 rows in set (0.00 sec)
client2执行如下操作:
mysql2> set autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql2> insert into t values (2),(100);
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
mysql2> select * from information_schema.tokudb_locks\G
*************************** 1. row ***************************
locks_trx_id: 283
locks_mysql_thread_id: 14
locks_dname: ./test/t-main
locks_key_left: 0001000000
locks_key_right: 0001000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
*************************** 2. row ***************************
locks_trx_id: 283
locks_mysql_thread_id: 14
locks_dname: ./test/t-main
locks_key_left: 000a000000
locks_key_right: 000a000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
*************************** 3. row ***************************
locks_trx_id: 283
locks_mysql_thread_id: 14
locks_dname: ./test/t-main
locks_key_left: 0064000000
locks_key_right: 0064000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
*************************** 4. row ***************************
locks_trx_id: 289
locks_mysql_thread_id: 16
locks_dname: ./test/t-main
locks_key_left: 0002000000
locks_key_right: 0002000000
locks_table_schema: test
locks_table_name: t
locks_table_dictionary_name: main
4 rows in set (0.00 sec)
mysql2> select @@tokudb_last_lock_timeout;
+--------------------------------------------------------------------------------------------------------------------+
| @@tokudb_last_lock_timeout |
+--------------------------------------------------------------------------------------------------------------------+
| {"mysql_thread_id":16, "dbname":"./test/t-main", "requesting_txnid":289, "blocking_txnid":283, "key":"0064000000"} |
+--------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
锁等待超时了，通过参数tokudb_last_lock_timeout得知，hash为0064000000的row-lock已经被txnid为283（client1)抢占。
总结
在使用TokuDB过程中，如果show processlist里有锁等待语句，可以通过tokudb_locks表获取到当前所有事务的锁信息，以快速定位到问题。
TokuDB提供tokudb_lock_timeout_debug参数，可以设置不同值(默认值为1)来记录锁冲突信息，说明如下：
tokudb_lock_timeout_debug = 0: No lock timeouts or lock deadlocks are reported.
tokudb_lock_timeout_debug = 1: A JSON document that describes the lock conflict is stored in the tokudb_last_lock_timeout session variable
tokudb_lock_timeout_debug = 2: A JSON document that describes the lock conflict is printed to the MySQL error log.
tokudb_lock_timeout_debug = 3: A JSON document that describes the lock conflict is stored in the 
