# mysqlnd_ms_xa_begin

(PECL mysqlnd_ms < 1.6.0)

mysqlnd_ms_xa_begin — Starts a distributed/XA transaction among MySQL servers

### 说明

mysqlnd_ms_xa_begin ( mixed `$connection` , string `$gtrid` [, int `$timeout` ] ) : int

Starts a XA transaction among MySQL servers. PECL/mysqlnd_ms acts as a transaction coordinator the distributed transaction.

Once a global transaction has been started, the plugin injects appropriate XA BEGIN SQL statements on all MySQL servers used in the following. The global transaction is either ended by calling mysqlnd_ms_xa_commit(), mysqlnd_ms_xa_rollback() or by an implicit rollback in case of an error.

During a global transaction, the plugin tracks all server switches, for example, when switching from one MySQL shard to another MySQL shard. Immediately before a query is run on a server that has not been participating in the global transaction yet, XA BEGIN is executed on the server. From a users perspective the injection happens during a call to a query execution function such as mysqli_query(). Should the injection fail an error is reported to the caller of the query execution function. The failing server does not become a participant in the global transaction. The user may retry executing a query on the server and hereby retry injecting XA BEGIN, abort the global transaction because not all required servers can participate, or ignore and continue the global without the failed server.

Reasons to fail executing XA BEGIN include but are not limited to a server being unreachable or the server having an open, concurrent XA transaction using the same xid.

Please note, global and local transactions are mutually exclusive. You cannot start a XA transaction when you have a local transaction open. The local transaction must be ended first. The plugin tries to detect this conflict as early as possible. It monitors API calls for controlling local transactions to learn about the current state. However, if using SQL statements for local transactions such as BEGIN, the plugin may not know the current state and the conflict is not detected before XA BEGIN is injected and executed.

The use of other XA resources but MySQL servers is not supported by the function. To carry out a global transaction among, for example, a MySQL server and another vendors database system, you should issue the systems SQL commands yourself.

> Note: Experimental

> The feature is currently under development. There may be issues and/or feature limitations. Do not use in production environments.

### 参数

`connection`

  A MySQL connection handle obtained from any of the connect functions of the mysqli, mysql or PDO_MYSQL extensions.

`gtrid`

  Global transaction identifier (gtrid). The gtrid is a binary string up to 64 bytes long. Please note, depending on your character set settings, 64 characters may require more than 64 bytes to store.

  In accordance with the MySQL SQL syntax, XA transactions use identifiers made of three parts. An xid consists of a global transaction identifier (gtrid), a branch qualifier (bqual) and a format identifier (formatID). Only the global transaction identifier can and needs to be set.

  The branch qualifier and format identifier are set automatically. The details should be considered implementation dependent, which may change without prior notice. In version 1.6 the branch qualifier is consecutive number which is incremented whenever a participant joins the global transaction.

`timeout`

  Timeout in seconds. The default value is 60 seconds.

  The timeout is a hint to the garbage collection. If a transaction is recorded to take longer than expected, the garbage collection begins checking the transactions status.

  Setting a low value may make the garbage collection check the progress too often. Please note, checking the status of a global transaction may involve connecting to all recorded participants and possibly issuing queries on the servers.

### 返回值

Returns `TRUE` if there is no open local or global transaction and a new global transaction can be started. Otherwise, returns `FALSE`

### 参见

- Quickstart XA/Distributed transactions
- Runtime configuration
- mysqlnd_ms_get_stats() - Returns query distribution and connection statistics