说GTID - 与GTID相关的4个基本函数和使用场景

4个基本函数

1. GTID_SUBSET(set1,set2) - 若在set1中的GTID，也在set2中，返回true，否则返回false（set1是set2的子集）。

[root@mysql.sock][(none)]> SELECT GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:23','3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57');

+-----------------------------------------------------------------------------------------------------+

| GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:23','3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57') |

+-----------------------------------------------------------------------------------------------------+

|                                                                                                   1 |

+-----------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

[root@mysql.sock][(none)]> SELECT GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:20-25','3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57');

+--------------------------------------------------------------------------------------------------------+

| GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:20-25','3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57') |

+--------------------------------------------------------------------------------------------------------+

|                                                                                                      0 |

+--------------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

2. GTID_SUBTRACT(set1,set2) - 返回在set1中，不在set2中的GTID集合（set1和set2的差集）。

[root@mysql.sock][(none)]> SELECT GTID_SUBTRACT('3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57','3E11FA47-71CA-11E1-9E33-C80AA9429562:20-25');

+----------------------------------------------------------------------------------------------------------+

| GTID_SUBTRACT('3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57','3E11FA47-71CA-11E1-9E33-C80AA9429562:20-25') |

+----------------------------------------------------------------------------------------------------------+

| 3e11fa47-71ca-11e1-9e33-c80aa9429562:26-57                                                               |

+----------------------------------------------------------------------------------------------------------+

1 row in set (0.01 sec)

[root@mysql.sock][(none)]> SELECT GTID_SUBTRACT('3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57','3E11FA47-71CA-11E1-9E33-C80AA9429562:23-24');

+----------------------------------------------------------------------------------------------------------+

| GTID_SUBTRACT('3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57','3E11FA47-71CA-11E1-9E33-C80AA9429562:23-24') |

+----------------------------------------------------------------------------------------------------------+

| 3e11fa47-71ca-11e1-9e33-c80aa9429562:21-22:25-57                                                         |

+----------------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

3. WAIT_FOR_EXECUTED_GTID_SET(gtid_set[, timeout]) - 等待gtid_set执行完，即GTID_SUBSET(gtid_subset, @@GLOBAL.gtid_executed)成立。timeout是可选的，超时参数。函数返回0，代表成功；返回1，代表超时；返回其它值，代表出错。

[root@mysql.sock][(none)]> SELECT WAIT_FOR_EXECUTED_GTID_SET('c4e5d4a0-a9be-11e9-b444-080027f22add:1-5',5);

+--------------------------------------------------------------------------+

| WAIT_FOR_EXECUTED_GTID_SET('c4e5d4a0-a9be-11e9-b444-080027f22add:1-5',5) |

+--------------------------------------------------------------------------+

|                                                                        0 |

+--------------------------------------------------------------------------+

1 row in set (0.00 sec)

4. WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS(gtid_set[, timeout][,channel]) - 和WAIT_FOR_EXECUTED_GTID_SET()类似，多了channel参数。

使用场景

1. 检查slave节点上是否执行了master上的所有GTIDs。

在salve节点上执行，SELECT GTID_SUBSET(master_gtid_executed, slave_gtid_executed)，若返回0，说明slave节点上还有GTIDs未执行。

在slave节点上执行，SELECT GTID_SUBTRACT(master_gtid_executed, slave_gtid_executed)，若返回GTIDs，也说明slave节点上还有GTIDs未执行。