Mysql deadlock timeout8/10/2023 ![]() ![]() do not retry if we get any other error out.println( "Sleep was interrupted." + e1) we still want to retry, even though sleep was The following is a sample Java code to catch and retry -911, -912, and -904 SQL Return Codes: for ( int i = 0 i + e) The application code can submit or rollback changes and executes retry logic. 912: The application receives this SQL code when there is a deadlock or timeout.The application code does not need to roll back because this SQL code causes the transaction to be rolled back. 911: The application receives this SQL code when the maximum number of locks for a database was reached because insufficient memory was allocated to the lock list.904: This SQL code is returned when a SQL statement was terminated because the resource limit was exceeded.There are three SQL codes that your application can handle using retry logic: ![]() Make sure your application releases resources as soon as it is deemed appropriate. Use User Uncommitted Read as much as possible (if appropriate).This command tells DB2 that the ambiguous cursor is read-only. Here are four more recommendations for reducing the number of locks: Your SQL statement is said to be ambiguous if it does include any of the above statements, Therefore, the lock might contain issues against the resource involved in the statement. Locking can be prevented in read-only mode, not ambiguous statements using the Uncommitted Read Isolation Level.Īn SQL statement is considered read-only when it uses any of the following: Table 1: DB2 Isolation Levels and the Phenomena That Can Occur When Each Is Used The correct use of isolation levels allows your application to be more concurrent (allows multi-user access to the data) and prevents against such database phenomena as Lost Updates, Dirty Reads, Nonrepeatable Reads, and Phantoms (you can read more about these topics in my article “ Database Isolation Levels“). ![]() The creation of locks can be avoided by using an isolation level mechanism available in all transactional databases. Deadlocks are situations in which multiple processes accessing the same database each hold locks needed by the other processes in such a way that none of the processes can proceed. Locking is a complex subject that requires a separate discussion, but for the purpose of this article, I will say that locking is supposed to be a temporary event-this means that if a resource is locked now, it will be released after some time. Applications that interact with the database must be designed to handle locks and resource unavailability situations. ![]() This mechanism exists to preserve data consistency. Locking occurs when one transaction obtains a lock on a resource so that another transaction cannot modify this resource. Furthermore, this article will explain how to avoid locking issues.Įven though the concepts discussed in this article pertain to almost all transactional databases and client applications that use them, do keep in mind that this article uses DB2 (version 9) and Java as points of reference. This article is designed to introduce the concepts of retry logic related to database transaction locking and unavailability. These situations need to be handled programmatically within your code. Every application that utilizes a relational database can encounter situations where data is deadlocked or unavailable. ![]()
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