![]() The same information as for the first lock. The waiter with process id and lock mode (X, U, S etc.) and request type (WAIT).ĭetailed information about the second lock. The list of waiter of this resource can be more than one. The owner with process id and lock mode (X, U, S etc.) The list of owner of this resource, mostly one process. PAGE locks)ĭetailed information about the first lock itself, they will be discussed later. Mostly only a list of two KEY locks, but might be other as well (e.g. Process number two, the survivor or winner of the deadlockĪll the resources that are involved in the deadlock. Has the statement from the ExecutionStack included. The complete input buffer of the process, in an SAP system most of the time only one statement, in our example the complete script of the connection. The statement that causes the deadlock, which SQL Handle and (sometimes) as a prepared statement. This section contains many attributes about the Process itself, they will be discussed later The list of involved Processes (most of the time only two) The surrounding bracket around all deadlocks (most of the time only one) deadlocks The name of the index, on which the locks are held or requested. ![]() The name of the object can be retrieved via the OBJECT_NAME function. The ObjectID that is associated to the HoBt ID. Heap or B-Tree ID, the ID of the internal allocation structure of the table or partition Common values are “Key Lock”, “Page Lock” or ”RID Lock” Type of lock the thread holds or requests. In the middle of the graph, in the rectangles, information about the two participating locks is shown: Line The amount of transaction log, that was already generated by this threadĪn internal reference number for the transaction.Īn internal reference number for the state of the transaction. If the thread has an associated deadlock priority, it is shown here. When the query is executed in parallel, this shows the ID of one of the parallel running threads. The ovals are showing more information about the thread: LineĪn internal reference number for the batch, where the statement is running in. If it is not set, the other trace flags will not be able to write to the SQL Server Error log. This trace flag is necessary to get the above debug information into the error log. This trace flag pipes XML Deadlock information to the error log ![]() XML Deadlock Information to the error log This trace flag produces detailed information about deadlocks, including participants and victims. I’m also available for consulting if you just don’t have time for that and need to solve performance problems quickly.The trace flags that get set are: Trace flag I’m offering a 75% discount to my blog readers if you click from here. If this is the kind of SQL Server stuff you love learning about, you’ll love my training. If your critical read and write queries are at odds with each other, look into an optimistic isolation level.If your modification queries are horror shows, see if you can separate them into parts.Look at your modification queries that modify lots of rows, and try batching them.Look at your modification queries that have WHERE clauses, and make sure they have the right indexes.If you have a locking problem, here’s what you should do: With index order switched, we take more fine-grained locks, and we take them for a shorter period of time. ON dbo.Users(Reputation, CreationDate DESC) Sought Only Keys Now If we change our index to have Reputation first, something nice happens. ![]() The optimizer isn’t asking for a missing index here, either (okay, I don’t blame it for a query that runs in 145ms, but stick with me). It’s helpful because we read far less pages than we would if we just scanned the clustered index, but the Reputation column being second means we can’t seek to rows we want. What’s going on here is that the optimizer chooses our narrower index to find data to update. WHERE u.Reputation = 147 Scanno Objectified So now we know whose fault it is that we have this index, and we know who to blame when this happens. ON dbo.Users(CreationDate DESC, Reputation) Maybe it’ll find users who created accounts in the last day who haven’t gotten any upvotes.Īn okay index to help us find data and avoid sorting data would look like this: CREATE INDEX ix_apathy WHERE u.CreationDate >= DATEADD(DAY, DATEDIFF(DAY, 0, GETDATE()), 0) SELECT u.DisplayName, u.Reputation, u.CreationDate Let’s say we have a super important query. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |