SELECT * FROM INFORMATION_SCHEMA.INNODB_LOCKS;
SELECT * FROM INFORMATION_SCHEMA.INNODB_TRX;
MySQL中information_schema 简略的介绍了Mysql中元数据信息库的各个表的作用，从这篇wiki中可以大致了解各个表的作用。这里主要介绍下Innodb事务锁相关的三个表：INNODB_TRX表、INNODB_LOCKS表、INNODB_LOCK_WAITS表。通过查看这三个表可以事务加锁的情况以及事务锁等待的情况，从而可以更简单地监控当前事务并分析可能存在的锁问题，例如分析死锁。
下面先分别介绍下三个表的作用以及各个字段的意义。
1、INNODB_TRX 表
The INNODB_TRX table contains information about every transaction currently executing inside InnoDB, including whether the transaction is waiting for a lock, when the transaction started, and the SQL statement the transaction is executing, if any.
INNODB_TRX表主要是包含了正在InnoDB引擎中执行的所有事务的信息，包括waiting for a lock和running的事务
INNODB_TRX表的各个字段
| Column name |
Description |
|---|---|
| trx_id | InnoDB存储引擎内部唯一的事务ID |
| trx_state | 当前事务的状态： RUNNING, LOCK WAIT, ROLLING BACK or COMMITTING. |
| trx_started | 事务的开始时间 |
| trx_requested_lock_id | 事务等待的锁的ID（如果事务状态不是LOCK WAIT，这个字段是NULL），详细的锁的信息可以连查INNODB_LOCKS表 |
| trx_wait_started | 事务等待开始的时间 （如果事务状态不是LOCK WAIT，这个字段是NULL） |
| trx_weight | 事务的权重，反映了一个事务修改和锁住的行数。当发生死锁回滚的时候，优先选择该值最小的进行回滚 |
| trx_mysql_thread_id | Mysql中的线程ID，show processlist显示的结果 |
| trx_query | 事务运行的sql语句 |
| trx_operation_state | 事务当操作的类型 如updating or deleting，starting index read等 |
| trx_tables_in_use | 查询用到的表的数量 |
| trx_tables_locked | 查询加行锁的表的数量 |
| trx_lock_structs | The number of locks reserved by the transaction |
| trx_lock_memory_bytes | 锁在内存占用的空间大小 |
| trx_rows_locked | 事务锁住的行数（不是准确数字） |
| trx_rows_modified | 事务插入或者修改的行数 |
| trx_concurrency_tickets | A value indicating how much work the current transaction can do before being swapped out, as specified by the innodb_concurrency_ticketsoption. |
| trx_isolation_level | 隔离级别 |
| trx_unique_checks | 唯一键检测 是否开启 |
| trx_foreign_key_checks | 外键检测 是否开启 |
| trx_last_foreign_key_error | Detailed error message for last FK error, or NULL. |
| trx_adaptive_hash_latched | Whether or not the adaptive hash index is locked by the current transaction. (Only a single transaction at a time can modify the adaptive hash index.) |
| trx_adaptive_hash_timeout | Whether to relinquish the search latch immediately for the adaptive hash index, or reserve it across calls from MySQL. When there is no AHI contention, this value remains zero and statements reserve the latch until they finish. During times of contention, it counts down to zero, and statements release the latch immediately after each row lookup. |
2、INNODB_LOCKS表
The INNODB_LOCKS table contains information about each lock that an InnoDB transaction has requested but not yet acquired, and each lock that a transaction holds that is blocking another transaction.
INNODB_LOCKS表主要包含了InnoDB事务锁的具体情况，包括事务正在申请加的锁和事务加上的锁。
INNODB_LOCKS表的各个字段
| Column name |
Description |
|---|---|
| lock_id | 锁ID |
| lock_trx_id | 事务ID, 可以连INNODB_TRX表查事务详情 |
| lock_mode | 锁的模式： S, X, IS, IX, S_GAP, X_GAP, IS_GAP, IX_GAP, or AUTO_INC |
| lock_type | 锁的类型，行级锁 或者表级锁 |
| lock_table | 加锁的表 |
| lock_index | 如果是lock_type='RECORD' 行级锁 ,为锁住的索引，如果是表锁为null |
| lock_space | 如果是lock_type='RECORD' 行级锁 ,为锁住对象的Tablespace ID，如果是表锁为null |
| lock_page | 如果是lock_type='RECORD' 行级锁 ,为锁住页号，如果是表锁为null |
| lock_rec | 如果是lock_type='RECORD' 行级锁 ,为锁住页号，如果是表锁为null |
| lock_data | 事务锁住的主键值，若是表锁，则该值为null |
3、INNODB_LOCK_WAITS表
The INNODB_LOCK_WAITS table contains one or more rows for each blocked InnoDB transaction, indicating the lock it has requested and any locks that are blocking that request.
INNODB_LOCK_WAITS表包含了blocked的事务的锁等待的状态
| Column name |
Description |
|---|---|
| requesting_trx_id | 申请锁资源的事务ID |
| requesting_lock_id | 申请的锁的ID |
| blocking_trx_id | 租塞的事务ID |
| blocking_lock_id | 租塞的锁的ID |
insert into test(test_id) values(5);
select * from test where test_id =5 for update;
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