For more on transaction locking, see Transaction locking and row versioning guide.įor more specific information on identification and prevention of deadlocks in Azure SQL Database, see Analyze and prevent deadlocks in Azure SQL Database. Deadlocks are caused competing, concurrent locks in the database, often in multi-step transactions. This article discusses deadlocks in the SQL Server Database Engine in depth. ( "Will try the transaction again.Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) try again at least once at this point. it was chosen as a victim of a deadlock. See Database-Side JDBC Procedures and SQLExceptions. catch such exceptions only at the outermost level of note: do not catch such exceptions in database-side methods
then try again if the deadlock victim exception put the whole thing in a try/catch block
DATABASE DEADLOCK EXCEPTION CODE
/ if this code might encounter a deadlock,
DATABASE DEADLOCK EXCEPTION HOW TO
The following code is one example of how to handle a deadlock timeout. In the case of a lock wait timeout, you probably do not want to do this right away. In the case of a deadlock you might want to re-try the transaction that was chosen as a victim. To do this, test for SQLExceptions with SQLStates of 40001 (deadlock timeout) or 40XL1 or 40XL2 (lockwait timeout). When you configure your system for deadlock and lockwait timeouts and an application could be chosen as a victim when the transaction times out, you should program your application to handle this.
A configuration in which no deadlock checking occurs: transactions time out after they have waited 50 seconds. Another typical configuration: deadlock checking occurs after a transaction has waited 60 seconds for a lock after 90 seconds, the transaction times out and is rolled back.įigure 9. One possible configuration: deadlock checking occurs when a transaction has waited 30 seconds no lock wait timeouts occur.įigure 8. This means that transactions never time out, although Derby can choose a transaction as a deadlock victim.įigure 7. If it is set to a value equal to or higher than the, the transaction times out before Derby does any deadlock checking.īy default, is set to 60 seconds. For example, in order for any deadlock checking to occur, the property must be set to a value lower than the property. When configuring your database or system, you should consider these properties together. You configure the amount of time a transaction waits before timing out with the property. You configure the amount of time a transaction waits before Derby does any deadlock checking with the property. Non-database deadlocks caused by Java synchronization primitives are not detected by Derby. Deadlocks across multiple databases are not detected. Note: Deadlocks are detected only within a single database. Waiting XID : The selected victim is XID : 752įor information on configuring when deadlock checking occurs, see Configuring Deadlock Detection and Lock Wait Timeouts. ERROR 40001: A lock could not be obtained due to a deadlock, The error message gives you the transaction IDs, the statements, and the status of locks involved in a deadlock situation. When Derby aborts the victim transaction, it receives a deadlock error (an SQLException with an SQLState of 40001).
(This may not be the case, however the transaction might have recently been escalated from row-level locking to table locking and thus hold a small number of locks even though it has done the most work.) Derby must pick one transaction as the victim and abort that transaction it picks the transaction that holds the fewest number of locks as the victim, on the assumption that transaction has performed the least amount of work.
Usually aborting one transaction breaks the deadlock. When Derby analyzes such a situation for deadlocks it tries to determine how many transactions are involved in the deadlock (two or more). When a transaction waits more than a specific amount of time to obtain a lock (called the deadlock timeout), Derby can detect whether the transaction is involved in a deadlock.
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