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MySQL Tutorial - Transaction Waiting for a Data Lock

By: FYIcenter.com

(Continued from previous topic...)

How Long a Transaction Will Wait for a Data Lock?

If you issue a UPDATE or DELETE statement on a row that has an exclusive lock owned by another session, your statement will be blocked to wait for the other session to release the lock. But the wait will be timed out after the predefined innodb_lock_wait_timeout period, which is 50 seconds by default.

The tutorial exercise below shows what will happen if a transaction has been blocked and the lock wait timeout period has been reached:

(session 1)

mysql> START TRANSACTION;
Query OK, 0 rows affected (0.00 sec)

mysql> UPDATE fyi_links SET counts='777' where id=101;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

(Exclusive lock (X) placed on row id=101)

Switch to session 2:

(session 2)

mysql> START TRANSACTION;
Query OK, 0 rows affected (0.00 sec)

mysql> UPDATE fyi_links SET counts=888 where id=101;

(Blocked to wait for exclusive lock (X) on row id=101)
(50 seconds passed)

ERROR 1205 (HY000): Lock wait timeout exceeded; 
   try restarting transaction
   
(Transaction terminated with a rollback)

(Continued on next topic...)

  1. What Is a Transaction?
  2. How To Start a New Transaction?
  3. How To End the Current Transaction?
  4. How To Create a Table for Transaction Testing?
  5. How To Switch between Autocommit-On and Autocommit-Off Modes?
  6. How To Find Out the Current Transaction Mode?
  7. How To Start a New Transaction Explicitly?
  8. How To Commit the Current Transaction?
  9. How To Rollback the Current Transaction?
  10. What Happens to the Current Transaction If a START TRANSACTION Is Executed?
  11. What Happens to the Current Transaction If a DDL Statement Is Executed?
  12. What Happens to the Current Transaction If the Session Is Ended?
  13. What Happens to the Current Transaction If the Session Is Killed?
  14. How Does MySQL Handle Read Consistency?
  15. What Are Transaction Isolation Levels?
  16. How To View and Change the Current Transaction Isolation Level?
  17. What Is a Data Lock?
  18. How To Experiment Data Locks?
  19. How Long a Transaction Will Wait for a Data Lock?
  20. What Happens to Your Transactions When ERROR 1205 Occurred?
  21. What Is a Dead Lock?
  22. How To Experiment Dead Locks?
  23. What Happens to Your Transactions When ERROR 1213 Occurred?
  24. What Are Impacts on Applications from Locks, Timeouts, and DeadLocks?

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