## 12.19 Functions Used with Global Transaction Identifiers (GTIDs)

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 The functions described in this section are used with GTID-based replication. It is important to keep in mind that all of these functions take string representations of GTID sets as arguments. As such, the GTID sets must always be quoted when used with them. See [GTID Sets](replication-gtids-concepts.html#replication-gtids-concepts-gtid-sets) for more information.

 The union of two GTID sets is simply their representations as strings, joined together with an interposed comma. In other words, you can define a very simple function for obtaining the union of two GTID sets, similar to that created here:

```
CREATE FUNCTION GTID_UNION(g1 TEXT, g2 TEXT)
    RETURNS TEXT DETERMINISTIC
    RETURN CONCAT(g1,',',g2);
```

 For more information about GTIDs and how these GTID functions are used in practice, see [Section 17.1.3, “Replication with Global Transaction Identifiers”](replication-gtids.html).

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**Table 12.24 GTID Functions**

|                                                 Name                                                  |                             Description                             |Deprecated|
|-------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------|----------|
|                      [`GTID_SUBSET()`](gtid-functions.html#function_gtid-subset)                      | Return true if all GTIDs in subset are also in set; otherwise false.|          |
|                    [`GTID_SUBTRACT()`](gtid-functions.html#function_gtid-subtract)                    |           Return all GTIDs in set that are not in subset.           |          |
|       [`WAIT_FOR_EXECUTED_GTID_SET()`](gtid-functions.html#function_wait-for-executed-gtid-set)       |       Wait until the given GTIDs have executed on the replica.      |          |
|[`WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS()`](gtid-functions.html#function_wait-until-sql-thread-after-gtids)|                 Use `WAIT_FOR_EXECUTED_GTID_SET()`.                 |  8.0.18  |

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  [`GTID_SUBSET(*`set1`*,*`set2`*)`](gtid-functions.html#function_gtid-subset)

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   Given two sets of global transaction identifiers *`set1`* and *`set2`*, returns true if all GTIDs in *`set1`* are also in *`set2`*. Returns false otherwise.

   The GTID sets used with this function are represented as strings, as shown in the following examples:

  ```
  mysql> SELECT GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:23',
      ->     '3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57')\G
  *************************** 1. row ***************************
  GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:23',
      '3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57'): 1
  1 row in set (0.00 sec)

  mysql> SELECT GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:23-25',
      ->     '3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57')\G
  *************************** 1. row ***************************
  GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:23-25',
      '3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57'): 1
  1 row in set (0.00 sec)

  mysql> SELECT GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:20-25',
      ->     '3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57')\G
  *************************** 1. row ***************************
  GTID_SUBSET('3E11FA47-71CA-11E1-9E33-C80AA9429562:20-25',
      '3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57'): 0
  1 row in set (0.00 sec)
  ```

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  [`GTID_SUBTRACT(*`set1`*,*`set2`*)`](gtid-functions.html#function_gtid-subtract)

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   Given two sets of global transaction identifiers *`set1`* and *`set2`*, returns only those GTIDs from *`set1`* that are not in *`set2`*.

   All GTID sets used with this function are represented as strings and must be quoted, as shown in these examples:

  ```
  mysql> SELECT GTID_SUBTRACT('3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57',
      ->     '3E11FA47-71CA-11E1-9E33-C80AA9429562:21')\G
  *************************** 1. row ***************************
  GTID_SUBTRACT('3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57',
      '3E11FA47-71CA-11E1-9E33-C80AA9429562:21'): 3e11fa47-71ca-11e1-9e33-c80aa9429562:22-57
  1 row in set (0.00 sec)

  mysql> SELECT GTID_SUBTRACT('3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57',
      ->     '3E11FA47-71CA-11E1-9E33-C80AA9429562:20-25')\G
  *************************** 1. row ***************************
  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 (0.00 sec)

  mysql> SELECT GTID_SUBTRACT('3E11FA47-71CA-11E1-9E33-C80AA9429562:21-57',
      ->     '3E11FA47-71CA-11E1-9E33-C80AA9429562:23-24')\G
  *************************** 1. row ***************************
  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 (0.01 sec)
  ```

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  [`WAIT_FOR_EXECUTED_GTID_SET(*`gtid_set`*[, *`timeout`*])`](gtid-functions.html#function_wait-for-executed-gtid-set)

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   Wait until the server has applied all of the transactions whose global transaction identifiers are contained in *`gtid_set`*; that is, until the condition GTID\_SUBSET(*`gtid_subset`*, `@@GLOBAL.gtid_executed`) holds. See [Section 17.1.3.1, “GTID Format and Storage”](replication-gtids-concepts.html) for a definition of GTID sets.

   If a timeout is specified, and *`timeout`* seconds elapse before all of the transactions in the GTID set have been applied, the function stops waiting. *`timeout`* is optional, and the default timeout is 0 seconds, in which case the function always waits until all of the transactions in the GTID set have been applied.

  `WAIT_FOR_EXECUTED_GTID_SET()` monitors all the GTIDs that are applied on the server, including transactions that arrive from all replication channels and user clients. It does not take into account whether replication channels have been started or stopped.

   For more information, see [Section 17.1.3, “Replication with Global Transaction Identifiers”](replication-gtids.html).

   GTID sets used with this function are represented as strings and so must be quoted as shown in the following example:

  ```
  mysql> SELECT WAIT_FOR_EXECUTED_GTID_SET('3E11FA47-71CA-11E1-9E33-C80AA9429562:1-5');
          -> 0
  ```

   For a syntax description for GTID sets, see [Section 17.1.3.1, “GTID Format and Storage”](replication-gtids-concepts.html).

   For `WAIT_FOR_EXECUTED_GTID_SET()`, the return value is the state of the query, where 0 represents success, and 1 represents timeout. Any other failures generate an error.

  [`gtid_mode`](replication-options-gtids.html#sysvar_gtid_mode) cannot be changed to OFF while any client is using this function to wait for GTIDs to be applied.

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  [`WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS(*`gtid_set`*[, *`timeout`*][,*`channel`*])`](gtid-functions.html#function_wait-until-sql-thread-after-gtids)

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  `WAIT_UNTIL_SQL_THREAD_AFTER_GTIDS()` is deprecated. Use `WAIT_FOR_EXECUTED_GTID_SET()` instead, which works regardless of the replication channel or user client through which the specified transactions arrive on the server.

