Process id=process202a2968ca8 taskpriority=0 logused=308 Once the flag is activated, we get the following info printed in the SQL error log when the previous deadlock situation occurs.ĭBCC TRACEON 1222, server process ID (SPID) 58. You can activate the 1222 trace flag like this: The 1222 flag captures more detailed info about the lock objects that are being deadlocked. You can see the sessions that are deadlocked, as well as the statements they were executing and the exclusive locks they are both holding.Īfter you have finished capturing the deadlock info, you should disable the trace flag, like this: SPID: 58 ECID: 0 Statement Type: UPDATE Line #: 1 SPID: 61 ECID: 0 Statement Type: UPDATE Line #: 1 This is an informational message only no user action is required.ĭeadlock encountered. Now, with the flag in place, we can capture the deadlock info:ĭBCC TRACEON 1204, server process ID (SPID) 58. You can activate the 1204 trace flag like this: The 1204 flag captures some basic info about the lock objects that are participating in a deadlock. There’s an overhead associated with activating these trace flags, so you should disable them once you finish capturing the deadlock info you were interested in. Once the flags are activated, you can find the deadlock info by accessing the sp_readerrorlog stored procedure. SQL Server provides a wide variety of trace flags, which you can activate at runtime and change the default behavior of the database engine.įor tracking deadlocks, there are two trace flags you can use: 1204, 1222. To track the resources involved in a deadlock, we are going to use the SQL Server deadlock trace flags. Transaction (Process ID 66) was deadlocked on lock resources with another processĪnd has been chosen as the deadlock victim. UPDATE post SET title = 'BASE' WHERE id = 1 UPDATE post_details SET updated_by = 'Bob' WHERE post_id = 1 Bob wants to update the PostDetails entity UPDATE post SET title = 'ACID' WHERE id = 1 UPDATE post_details SET updated_by = 'Alice' WHERE post_id = 1 When running the SQL statements depicted in the diagram above, we get the following SQL Server deadlock error: So, no matter if you are using 2PL or MVCC, exclusive locks are always acquired when modifying a table row, and, for this reason, there’s always the possibility of getting a database deadlock. Only SQL Server uses the 2PL concurrency control mechanism by default, although you can also switch MVCC using the Read Committed Snapshot Isolation or the Snapshot Isolation levels. While the 2PL algorithm is easy to implement, it incurs too much locking, as a shared lock is required to be obtained prior to reading any database record.Īnd, because locking can impact transaction throughput, most relational database systems (e.g., Oracle, PostgreSQL, and the MySQL InnoDB engine) use MVCC (Multi-Version Concurrency Control) to avoid taking shared locks upon reading a database record. When relational database systems were first implemented, the 2PL (Two-Phase Locking) concurrency control mechanism was used to ensure consistency and data integrity. Every time a database record has to be modified, an exclusive lock is acquired to ensure that the row state is changed from one consistent state to another. And, since SQL Server uses 2PL by default, it’s not uncommon to have to track deadlock issues that affect application performance.Īll relational database systems use locking. In this article, I’m going to explain how you can find the cause of an SQL Server deadlock using trace flags and the SQL error log.Īs a rule of thumb, the more locks are acquired, the higher the probability of a deadlock. So, enjoy spending your time on the things you love rather than fixing performance issues in your production system on a Saturday night! Well, Hypersistence Optimizer is that tool!Īnd it works with Spring Boot, Spring Framework, Jakarta EE, Java EE, Quarkus, or Play Framework. Follow having a tool that can automatically detect JPA and Hibernate performance issues.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |