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In TDSQL for MySQL, a transaction usually involves data of multiple physical nodes. Such transactions are called distributed transactions.
TDSQL supports XA and non-XA distributed transaction protocols. By default, TDSQL (kernel version 5.7 or later) supports distributed transactions which are imperceptible to the client and as easy-to-use as non-distributed transactions.
Distributed transactions in TDSQL adopt a two-phase commit protocol (2PC) to ensure the atomicity and consistency of transactions, and support such isolation levels as Read committed, Repeatable read, and Serializable.

Non-XA Distributed Transactions

begin;     # Start a transaction
...    # Cross-set INSERT, DELETE, UPDATE, SELECT, and other non-DDL operations
commit;    # Commit the transaction

XA Distributed Transactions

XA distributed transactions refer to cross-instance transactions.

xa begin ''; # Start an XA transaction. The transaction identifier is generated by the system, so you can pass in an empty string.
...    # Cross-set INSERT, DELETE, UPDATE, SELECT, and other non-DDL operations
select gtid();   # Get the XA transaction identifier, which is assumed as 'xid' in the following statements
xa prepare 'xid';    # Prepare the transaction
xa commit/rollback 'xid'; # Commit or roll back the transaction

New Transactions APIs

• select gtid(): this API is used to get the globally unique identifier of the distributed transaction. If no value is returned, the transaction is not a distributed transaction.

  • The format of non-XA distributed transaction identifier is: 'Gateway ID' - 'Proxy random value' - 'Serial number' - 'Timestamp' - 'Partition number', such as c46535fe-b6-dd-595db6b8-25.
  • The format of XA distributed transaction identifier is: 'ex' - 'Gateway ID' - 'Proxy random value' - 'Serial number' - 'Timestamp' - 'Partition number', such as ex-c46535fe-b6-dd-595db6b8-25.

• select gtid_state("Globally unique identifier of the distributed transaction"): this API is used to get the transaction status (in 3 seconds by default) after an exception occurs in committing the transaction. The following status may be returned:

  • COMMIT: indicates that the transaction has been or is going to be committed.
  • ABORT: indicates that the transaction is going to be rolled back.
  • Empty value: the transaction status will be cleared after an hour, so there are two possibilities:
    • For a query after an hour, it indicates that the transaction status has been cleared.
    • For a query within an hour, it indicates that the transaction is going to be rolled back.

• xa boost 'Globally unique identifier of the distributed transaction': after an exception occurs in committing a non-XA transaction, the transaction will be automatically committed or rolled back by the backend component in a certain period of time (30 seconds by default). If you are unwilling to wait for such a long time, you can repeatedly call this API to make the system commit or roll back the transaction in a timely manner. This API will return the status of the transaction (i.e., committed or rolled-back).

• xa lockwait: this API is used to show the wait-for relationship between the distributed transactions. You can convert it to a graph using the dot tool.

• xa show: this API is used to show transactions that are active on the proxy.