![]() I understand that solution for this problem may be creating critical section in code but I'm trying to understand why Serializable Isolation Level doesn't do the trick. I will update the question in few minutes and post graph from sql server profiler. Sql Server Profiler shows that deadlock is key lock. Originally, i'm using linq but I wanted to show simplified example. In our case, the deadlock victim is the process ID 65. The example is written using command objects but it's just for test purposes. Once a deadlock occurs, SQL Server will kill a deadlock victim. I think first select should lock row/table and won't let another select to obtain any locks. There are other SELECT queries running parallel on the same set of tables. I can't understand how it can happen using Serializable Isolation Level. Transaction (Process ID 69) was deadlocked on lock communication buffer resources with another process and has been chosen as the deadlock victim. On lock resources with another process and has beenĬhosen as the deadlock victim. : Exception: Transaction (Process ID 59) was deadlocked Then if I try to execute test method from two threads and they try to update same record I get following output: : Creating/updating session UpdateSession(sessionId, connection, transaction) If (GetSessionById(sessionId, connection, transaction) != null) ![]() Using (SqlTransaction transaction = connection.BeginTransaction(IsolationLevel.Serializable)) Using (SqlConnection connection = GetConnection()) ![]() Public void UpdateSessionTest(Guid sessionId) Protected int UpdateSession(Guid sessionId, SqlConnection connection, SqlTransaction transaction)Ĭommand.CommandText = "UPDATE SessionTest SET ExpirationTime = WHERE SessionId = connection Ĭ(new (20))) Using (SqlDataReader reader = command.ExecuteReader()) Using (SqlCommand command = new SqlCommand())Ĭommand.CommandText = "SELECT * FROM SessionTest WHERE SessionId = connection It is accomplished using following code: protected Guid? GetSessionById(Guid sessionId, SqlConnection connection, SqlTransaction transaction) I'm trying first to select a record from this table and if the record exists set expiration time to current time plus some interval. UNIQUEIDENTIFIER ROWGUIDCOL NOT NULL,ĬONSTRAINT PRIMARY KEY CLUSTERED (ĪDD CONSTRAINT I have recreated the situation in the following testcase. I read answers from this thread: SQL Server deadlocks between select/update or multiple selects but I still don't understand why I get deadlock. This is how distributed transactions using two-phase commit protocols (such as XA or COM+ Transactions) work.I'm having a problem with deadlock on SELECT/UPDATE on SQL Server 2008. The DBMS maintains the locks and allows you to pick the session back up through the TxID. In the latter case you open the transaction with the TxID and then reconnect using that ID. To use pessimistic locking you need either a direct connection to the database (as would typically be the case in a two tier client server application) or an externally available transaction ID that can be used independently of the connection. It has much better integrity than optimistic locking but requires you to be careful with your application design to avoid Deadlocks. Pessimistic Locking is when you lock the record for your exclusive use until you have finished with it. In this situation the client cannot actually maintain database locks as the connections are taken from a pool and you may not be using the same connection from one access to the next. This strategy is most applicable to high-volume systems and three-tier architectures where you do not necessarily maintain a connection to the database for your session. different version to yours) you abort the transaction and the user can re-start it. hasn't been updated between when you check the version and write the record to the disk) and update the version in one hit. to allow seeing multiple deadlocks simultaneously. 2 - Added individual items in the Execution Stack node. Insert the XML Deadlock Graph into the deadlock table. When you write the record back you filter the update on the version to make sure it's atomic. Shred XML Deadlock Graphs, showing in tabular format as much information as possible. Optimistic Locking is a strategy where you read a record, take note of a version number (other methods to do this involve dates, timestamps or checksums/hashes) and check that the version hasn't changed before you write the record back.
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