![]() ![]() The Information Events as listed below may be seen in the EV Event Logs on the DA server.Ī transient error is preventing the execution of a SQL command. When a large number of such messages is processed, the number and/or frequency of SQL deadlocks could increase and could potentially pause or stop Analytics processing. When such messages are processed by DA Analytics, the Analytics background processing of these messages may result in SQL deadlocks. These messages can be Archived by Enterprise Vault (EV) SMTP Archiving and can be found by Discovery Accelerator (DA) Searches. Before we do that let’s clean our tables and re-insert the data into it.Bloomberg messages can contain hundreds of recipients, with some numbering into the thousands. This time transaction1 will be selected as deadlock victim since it will have deadlock priority of NORMAL by default. In the next example, we will set the deadlock priority of transaction2 to HIGH and will again create a deadlock. Now if you select the data from table1 you should see updated data as shown below:ĭeadlock with Deadlock Priority set to High The error message is shown in the following screenshot: This means that transaction2 is the least expensive to rollback.Īfter some time, you will see SQL Server select transaction2 as the deadlock victim and it will then roll it back as expected. The first UPDATE statement of transaction1, it is updating five rows of table1 whereas the first UPDATE statement of transaction2 is updating only one row in table2. Now we know that by default, the deadlock priority for both of the transactions is NORMAL, therefore SQL server will select that transaction as deadlock victim which is least expensive to rollback. This statement tries to access table1 which is locked and at this stage a deadlock will occur. This statement tries to access table2 which is locked by transaction2.įinally, execute the second update statement in transaction2. Now execute the second update statement from transaction1. This will create locks on table1 and table2. First execute the first update statement from the first transaction and then execute the first update statement from the second transaction. The process of creating a deadlock is simple. Execute the following script on your SQL Server. We will use this data in our deadlock example. This is most easily explained by working through an example. In the unlikely event that both the deadlock priority and the cost of the transactions involved in the deadlock are equal, then deadlock victim will be selected randomly. If the priority of all the transactions involved in the deadlock is same, the transaction that is least expensive is chosen as deadlock victim. It can also be set to an integer value in the range of -10 to 10.Īs noted earlier, the process or transaction with the lowest deadlock priority is chosen as the deadlock victim. The process with the lowest deadlock priority will then be the one chosen as the deadlock victim.īy default the priority for all the processes is normal. However, users can set custom priorities for a particular transaction using the SET DEADLOCK_PRIORITY statement. ![]() In simple terms, a transaction that makes the fewest changes to the database is considered the least expensive. A 1205 error is sent to the application that was running the victim transaction.īy default, SQL Server chooses as the deadlock victim the transaction that is least expensive to rollback. Once this has been done, the victim transaction is rolled back and all of the resources held by the victim are released. When a deadlock is detected, SQL Server then needs to select a victim of the deadlock. If the lock monitor thread stops finding deadlocks the interval for deadlock detection is then periodically increased up to the default five seconds interval. If a deadlock is found, a victim is selected and the interval for the lock monitor thread is reduced, this can be to as low as 100 milliseconds in some cases. SQL Server runs a lock monitor thread every five seconds to check if any deadlocks have occurred. Why one process is selected as deadlock victim and not the other. In this article, we will look at the criteria on which SQL server selects a deadlock victim. We saw that SQL Server selects one of the processes involved in the deadlock as deadlock victim. In the article on Deadlock Analysis and Prevention, we saw how deadlock occurs. ![]()
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