XA Transactions in MySQL

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1 XA Transactions in MySQL An overview and troubleshooting guide to distributed transactions Dov Endress Senior MySQL DBA July 25th Percona

2 ACID Compliant Distributed Transactions Distributed Transaction Process Percona

3 ACID Defined As Atomic - committed as a whole Consistent - the data is either valid, or rolled back to the last valid state Isolated - uncommitted transactions are isolated from other transactions Durable - once committed, transactions stay committed 3

4 Distributed Transaction Processing The XA or extended Architecture specification, developed by the Open Group describes the interaction between a Transaction Manager and one or more Resource Managers. Resource managers are disparate data sets whose transactions must ensure ACID compliance internally and with each other. 4

5 XA Transaction Flow Sample transaction walkthrough Percona

6 XA Transaction Flow Transaction Manager creates distinct XID and instructs the Resource Managers to start the transaction XID sent to Resource Managers XA transaction initiated with XA START XID on Resource Managers XA Transaction Flow Transaction Manager Resource Manager Begin XA Transaction XA START XID Resource Manager XA START XID 6

7 XA Transaction Flow Resource Managers initiate and execute local transactions. Local transactions are isolated to Resource Managers and are independent of each other. XA Transaction Flow Transaction Manager Resource Manager Begin XA Transaction XA START XID Resource Manager XA START XID 7

8 XA Transaction Flow After issuing the XID, the Transaction Manager polls the Resource Managers for the transactions to come to a PREPARED state. XA Transaction Flow Transaction Manager Resource Manager Begin XA Transaction XA START XID Is XID prepared? Resource Manager XA START XID 8

9 XA Transaction Flow When they have completed the local transactions, the Resource Managers execute XA END and XA PREPARE on the XID. XA Transaction Flow Transaction Manager Resource Manager Begin XA Transaction XA START XID Is XID prepared? XA END XID XA PREPARE XID Resource Manager XA START XID XA END XID XA PREPARE XID 9

10 XA Transaction Flow Only when ALL Resource Managers have prepared the XID will the Transaction Manager give the command to EXECUTE. XA Transaction Flow Transaction Manager Resource Manager Begin XA Transaction XA START XID Is XID prepared? XA END XID XA PREPARE XID Commit XA Transaction Resource Manager XA START XID XA END XID XA PREPARE XID 10

11 XA Transaction Flow Receiving the PREPARED notification The Transaction Manager initiates the commit command when ALL Resource Managers report the XID prepared The Resource Managers execute XA COMMIT XID as an atomic unit* XA Transaction Flow Transaction Manager Resource Manager Resource Manager Begin XA Transaction XA START XID XA START XID Is XID prepared? XA END XID XA PREPARE XID XA END XID XA PREPARE XID Commit XA Transaction XA COMMIT XID XA COMMIT XID 11

12 Working with XA Transactions Interaction with Transactions, De-Bugging, and Investigative Techniques Percona

13 Command Overview XA START XID XA END XID XA PREPARE XID XA COMMIT XID XA ROLLBACK XID XA RECOVER [CONVERT XID] 13

14 XID Composition xid = gtrid [, bqual [, formatid ]] gtrid - global transaction identifier bqual - branch qualifier formatid - identifier of the format used by gtrid and bqual 14

15 Sample Tables and Trigger mysql> show create table t\g *************************** 1. row *************************** Table: t Create Table: CREATE TABLE `t` ( `id` int(7) NOT NULL AUTO_INCREMENT, `key_name` varchar(16) NOT NULL DEFAULT '', `val` varchar(256) NOT NULL DEFAULT '', PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 mysql> show create table t_i\g *************************** 1. row *************************** Table: t_i Create Table: CREATE TABLE `t_i` ( `id` int(7) NOT NULL AUTO_INCREMENT, `t_id` int(7) NOT NULL DEFAULT '0', `insert_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 mysql> show triggers like 't'\g *************************** 1. row *************************** Trigger: ins_after_ins Event: INSERT Table: t Statement: begin insert into t_i (id, t_id, insert_time) values (NULL, new.id, NOW()); end Timing: AFTER 15

16 Example Transaction 1 mysql> XA START 'foo'; Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO t (key_name,val) VALUES ('foo','bar'); Query OK, 1 row affected (0.00 sec) mysql> XA END 'foo'; Query OK, 0 rows affected (0.00 sec) mysql> XA PREPARE 'foo'; Query OK, 0 rows affected (0.01 sec) 16

17 XA RECOVER 1 [vagrant@mysql1 ~]$ sudo mysql -p Enter password: Welcome to the MySQL monitor. Commands end with ; or \g. mysql> use test; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> select * from t; Empty set (0.00 sec) mysql> XA RECOVER; formatid gtrid_length bqual_length data foo

18 XA COMMIT 1 Connection 1: mysql> XA COMMIT 'foo'; Query OK, 0 rows affected (0.00 sec) mysql> Connection 2: mysql> SELECT * FROM t; id key_name val foo bar row in set (0.00 sec) mysql> SELECT * FROM t_i; id t_id insert_time :51: row in set (0.00 sec) mysql> 18

19 Example Transaction 2 Connection 1 mysql> XA START '123456abcdefg','gfedcba',1234; Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO t (key_name,val) VALUES ('fop','bas'); Query OK, 1 row affected (0.00 sec) mysql> XA END '123456abcdefg','gfedcba',1234; Query OK, 0 rows affected (0.00 sec) mysql> XA PREPARE '123456abcdefg','gfedcba',1234; Query OK, 0 rows affected (0.00 sec) mysql> quit Bye [root@mysql1 log]# Connection 2 mysql> INSERT INTO t_i VALUES(2,2,' :00:01'); ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction mysql> 19

20 XA RECOVER and COMMIT Connection 2 mysql> XA RECOVER; formatid gtrid_length bqual_length data abcdefggfedcba row in set (0.00 sec) mysql> XA COMMIT '123456abcdefggfedcba'; ERROR 1397 (XAE04): XAER_NOTA: Unknown XID mysql> XA COMMIT '123456abcdefg','gfedcba',1234; Query OK, 0 rows affected (0.00 sec) 20

21 XA RECOVER CONVERT and COMMIT Converting the HEX value mysql> XA RECOVER CONVERT XID; formatid gtrid_length bqual_length data x row in set (0.01 sec) mysql> XA COMMIT '0x '; ERROR 1397 (XAE04): XAER_NOTA: Unknown XID mysql> XA COMMIT X' ',X' '; Query OK, 0 rows affected (0.01 sec) 21

22 InnoDB Engine Status TRANSACTIONS Trx id counter Purge done for trx's n:o < undo n:o < 0 state: running but idle History list length 3 LIST OF TRANSACTIONS FOR EACH SESSION: ---TRANSACTION , not started 0 lock struct(s), heap size 1136, 0 row lock(s) ---TRANSACTION , ACTIVE (PREPARED) sec recovered trx 2 lock struct(s), heap size 1136, 1 row lock(s), undo log entries 1 ---TRANSACTION , ACTIVE (PREPARED) sec recovered trx 1 lock struct(s), heap size 1136, 0 row lock(s), undo log entries 1 22

23 Example Transaction 3 mysql> XA START X'4F170100CFC2',X'6C61736C63'; Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO t (key_name,val) VALUES ('for','bat'); Query OK, 1 row affected (0.00 sec) mysql> XA RECOVER; formatid gtrid_length bqual_length data O??laslc row in set (0.00 sec) mysql> XA RECOVER CONVERT XID; formatid gtrid_length bqual_length data x4F170100CFC26C61736C row in set (0.00 sec) mysql> 23

24 Binary Log Entry XA START X'4f170100cfc2',X'6c61736c63',1 /*!*/; # at 8993 # :43:18 server id 303 end_log_pos 9043 CRC32 0x251f5c99 Table_map: `test`.`t` mapped to number 116 # at 9043 # :43:18 server id 303 end_log_pos 9092 CRC32 0xfb138fdb Table_map: `test`.`t_i` mapped to number 117 '/*!*/; ### INSERT INTO `test`.`t` ### SET ### INSERT INTO `test`.`t_i` ### SET 17:43:18' # at 9190 # :43:32 server id 303 end_log_pos 9295 CRC32 0x938e96e6 Query thread_id=13 exec_time=0 error_code=0 SET TIMESTAMP= /*!*/; XA END X'4f170100cfc2',X'6c61736c63',1 /*!*/; 24

25 Other Considerations and Limitations Only supported by InnoDB storage engine Distinct bqual MySQL only Flush tables with read lock Replication 25

26 Conclusion Synopsis + Q&A Percona

27 Champions DATABASE of Unbiased PERFORMANCE Open Source Database Performance Matters Database MATTERS Solutions 27

Chapter 8: Working With Databases & Tables

Chapter 8: Working With Databases & Tables o Working with Databases & Tables DDL Component of SQL Databases CREATE DATABASE class; o Represented as directories in MySQL s data storage area o Can t have