![]() ![]() Another advantage of this design is that we could change the extract method (we could use an extraction from SQL Server Error Log), remaining steps would be kept intact.Įach step of this process can be run asynchronously and uses the results of its predecessor to generate its output. So, we will divide the process into 3 steps as shown in following figure. This process could be built in one piece of code: we could do all the job inside a single stored procedure, like we did to extract deadlock occurrence time from SQL Server Error Log in the previous article, but the complexity of such a procedure would be very high. ![]() Now, let’s focus on a process for collecting and transforming XML version of deadlock graphs into something we can use for reporting, in short, something on which it’s easier to compute statistics. These columns will then be available to generate reports as we discussed just above.ĭeadlocks data processing using SQL Server Extended Events This article will define a process that will collect these XML descriptors into a base table and split them into a series of columns. These reports would be especially useful when we don’t always have the code of the application that generates these deadlocks and we must provide suitable information to the author to inform (and sometimes try to convince) them that it can be the root cause of performance problems then help him in solving these problems. This would allow us the ability to generate reports based on deadlock properties like the application name, queries implied in deadlocks… This means that we can do so much more than just store this XML. Now, it’s time to go deeper in the processing of this deadlock information…Īs we collect this information in XML format, we can query the XML contents directly in SQL Server using the XQuery feature of Transact-SQL. We also discussed a simple report which leads to the creation of a deadlock occurrences timeline. 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.In previous article entitled “ How to report on SQL Server deadlock occurrences“, we’ve seen how to extract deadlock information from either system_health or specialized Extended Event and store this information into a table in a SQL Server database. 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. The example is written using command objects but it's just for test purposes. I think first select should lock row/table and won't let another select to obtain any locks. I can't understand how it can happen using Serializable Isolation Level. 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. I'm having a problem with deadlock on SELECT/UPDATE on SQL Server 2008. ![]()
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