OceanBase 为了避免事务长时间不提交持有锁影响其他会话，设计了两个超时逻辑。一个是事务未提交超时，一个是事务空闲超时。分别由租户变量 ob_trx_idle_timeout 和 ob_trx_timeout 控制，默认值分别是120秒和100秒。通常只会有一个超时机制被触发。

  1. obclient> show variables where variable_name in ('ob_trx_idle_timeout','ob_trx_timeout');
  2. +---------------------+-----------+
  3. | VARIABLE_NAME       | VALUE     |
  4. +---------------------+-----------+
  5. | ob_trx_idle_timeout | 120000000 |
  6. | ob_trx_timeout      | 100000000 |
  7. +---------------------+-----------+
  8. 2 rows in set (0.00 sec)

关于事务空闲超时

OceanBase 的事务空闲时间超过一段时间还没有提交时，会自动断开连接并回滚事务，此时会话需要重新连接。

会话事务空闲超时时间阈值由租户变量 ob_trx_idle_timeout 控制，这个参数值建议不要小于100秒，实际空闲会话断开的时间会是在 [100s, 100s + ob_trx_idle_timeout ] 之间。

示例：事务空闲超时报错

下面示例先设置事务空闲超时时间为120秒，事务未提交超时时间为1000秒。当事务空闲时间超过120秒后，连接会被自动断开，事务也自动被 ROLLBACK 了。

  1. obclient> DROP TABLE IF EXISTS t_insert; 
  2. Query OK, 0 rows affected (0.01 sec)
  4. obclient> CREATE TABLE t_insert(
  5.     id bigint NOT NULL PRIMARY KEY auto_increment
  6.     , name varchar(10) NOT NULL
  7.     , value bigint
  8.     ,gmt_create timestamp NOT NULL DEFAULT current_timestamp
  9. );
  10. Query OK, 0 rows affected (0.05 sec)
  12. obclient> INSERT INTO t_insert(name, value) values('CN',NULL),('UK',NULL),('US',NULL);
  13. Query OK, 3 rows affected (0.00 sec)
  14. Records: 3  Duplicates: 0  Warnings: 0
  16. obclient> commit;
  17. Query OK, 0 rows affected (0.00 sec)
  19. obclient> select now(), * from t_insert t;
  20. +---------------------+----+------+-------+---------------------+
  21. | now()               | id | name | value | gmt_create          |
  22. +---------------------+----+------+-------+---------------------+
  23. | 2020-04-03 16:54:51 |  1 | CN   |  NULL | 2020-04-03 16:54:49 |
  24. | 2020-04-03 16:54:51 |  2 | UK   |  NULL | 2020-04-03 16:54:49 |
  25. | 2020-04-03 16:54:51 |  3 | US   |  NULL | 2020-04-03 16:54:49 |
  26. +---------------------+----+------+-------+---------------------+
  27. 3 rows in set (0.00 sec)
  29. obclient> set session ob_trx_timeout=1000000000;
  30. Query OK, 0 rows affected (0.00 sec)
  32. obclient> set session ob_trx_idle_timeout=120000000;
  33. Query OK, 0 rows affected (0.00 sec)
  35. obclient> update t_insert set gmt_create=now() where id=3;
  36. Query OK, 1 row affected (0.00 sec)
  37. Rows matched: 1  Changed: 1  Warnings: 0
  39. obclient> select now(), t.* from t_insert t;
  40. +---------------------+----+------+-------+---------------------+
  41. | now()               | id | name | value | gmt_create          |
  42. +---------------------+----+------+-------+---------------------+
  43. | 2020-04-03 16:55:30 |  1 | CN   |  NULL | 2020-04-03 16:54:49 |
  44. | 2020-04-03 16:55:30 |  2 | UK   |  NULL | 2020-04-03 16:54:49 |
  45. | 2020-04-03 16:55:30 |  3 | US   |  NULL | 2020-04-03 16:55:25 |
  46. +---------------------+----+------+-------+---------------------+
  47. 3 rows in set (0.00 sec)
  49. <<等100秒不操作>>
  51. obclient> select now(), t.* from t_insert t;
  52. ERROR-02013: Lost connection to MySQL server during query
  53. obclient> select now(), * from t_insert t;
  54. ERROR-02006: MySQL server has gone away
  55. No connection. Trying to reconnect...
  56. Connection id:    53246
  57. Current database: TPCC
  59. +---------------------+----+------+-------+---------------------+
  60. | now()               | id | name | value | gmt_create          |
  61. +---------------------+----+------+-------+---------------------+
  62. | 2020-04-03 16:57:41 |  1 | CN   |  NULL | 2020-04-03 16:54:49 |
  63. | 2020-04-03 16:57:41 |  2 | UK   |  NULL | 2020-04-03 16:54:49 |
  64. | 2020-04-03 16:57:41 |  3 | US   |  NULL | 2020-04-03 16:54:49 |
  65. +---------------------+----+------+-------+---------------------+
  66. 3 rows in set (0.00 sec)

关于事务未提交超时

OceanBase 的事务持续时间超过一段时间还没有提交，会报超时错误。此时会话需要明确发出 ROLLBACK 命令才可以继续在会话里执行 SQL。

会话事务的未提交超时时间阈值是由租户变量 ob_trx_timeout 控制。

示例：事务未提交超时报错

下面示例先设置事务空闲超时时间为120秒，事务超时时间为100秒。当一个事务未提交时间持续到100秒时，事务内部状态就变为超时状态，同时锁会释放。此后会话需要显式发出 ROLLBACK 语句。

  1. obclient> set session ob_trx_timeout=100000000;
  2. Query OK, 0 rows affected (0.00 sec)
  4. obclient> set session ob_trx_idle_timeout=120000000;
  5. Query OK, 0 rows affected (0.00 sec)
  7. obclient> update t_insert set gmt_create=sysdate() where id=3;
  8. Query OK, 1 row affected (0.00 sec)
  9. Rows matched: 1  Changed: 1  Warnings: 0
  11. obclient> select now(), t.* from t_insert t ;
  12. +---------------------+----+------+-------+---------------------+
  13. | now()               | id | name | value | gmt_create          |
  14. +---------------------+----+------+-------+---------------------+
  15. | 2020-04-03 16:59:56 |  1 | CN   |  NULL | 2020-04-03 16:54:49 |
  16. | 2020-04-03 16:59:56 |  2 | UK   |  NULL | 2020-04-03 16:54:49 |
  17. | 2020-04-03 16:59:56 |  3 | US   |  NULL | 2020-04-03 16:59:51 |
  18. +---------------------+----+------+-------+---------------------+
  19. 3 rows in set (0.00 sec)
  21. <<等120秒不操作>>
  23. obclient> select now(), t.* from t_insert t ;
  24. ERROR-00600: internal error code, arguments: -6210, Transaction is timeout
  25. obclient> commit;
  26. ERROR-00600: internal error code, arguments: -6210, Transaction is timeout
  27. obclient> rollback;
  28. Query OK, 0 rows affected (0.00 sec)
  30. obclient> select now(), t.* from t_insert t ;
  31. +---------------------+----+------+-------+---------------------+
  32. | now()               | id | name | value | gmt_create          |
  33. +---------------------+----+------+-------+---------------------+
  34. | 2020-04-03 17:04:13 |  1 | CN   |  NULL | 2020-04-03 16:54:49 |
  35. | 2020-04-03 17:04:13 |  2 | UK   |  NULL | 2020-04-03 16:54:49 |
  36. | 2020-04-03 17:04:13 |  3 | US   |  NULL | 2020-04-03 16:54:49 |
  37. +---------------------+----+------+-------+---------------------+
  38. 3 rows in set (0.00 sec)

注意：

建议不要将事务未提交超时参数设置小于1秒。