1/11/2024 0 Comments Sql deadlock with nolockThe current one has a couple of table with 130M rows. Nevertheless, should a decision be made to use NOLOCK table hint, it is recommended that you include the WITH keyword.Frans - I've worked on 2 systems that had considerable amounts of data. There are benefits and drawbacks to specifying NOLOCK table hint as a result they should not just be included in every T-SQL script without a clear understanding of what they do. For instance, I forgot to include NOLOCK inside opening and closing round brackets and this led to the query executing endlessly as it waited for a shared lock. If you forget to include NOLOCK inside round brackets then the NOLOCK hint can be mistaken for a table alias by the query optimiser, which means that the query would then have to wait for shared lock before it can start reading a given table. Without the WITH Keyword you simply have a table AliasĪt this point you should already be leaning towards always specifying the WITH keyword when using table hints but just to convince you further, omitting the WITH keyword can have undesirable consequences. The sample UPDATE script that we would need to run is shown in Script 1.įigure 6 3. In order to reflect this change, we would need to run an UPDATE statement against our SQL Server table. Now let’s assume that having seen his opponents’ jersey number, Lionel Messi later decides to change his jersey number from 10 to 7. A preview of this SQL Server table is shown in In the following sections, I will provide practical examples for using NOLOCK and WITH NOLOCK table hints.įor the purposes of this discussion, I will use a SQL Server 2016_FIFABallonDOr table that contains the top 3 footballers nominated for FIFA’s Ballon d’Or award in 2016. The only drawback is that using the NOLOCK table hint may accidentally result into reading uncommitted “dirty” data. The benefits of querying data using the NOLOCK table hint is that it requires less memory and prevents deadlocks from occurring with any other queries that may be reading similar data. However, the NOLOCK table hint allows you to instruct the query optimiser to read a given table without obtaining an exclusive or shared lock. This behaviour ensures that you are only reading committed data. The default behaviour in SQL Server is for every query to acquire its own shared lock prior to reading data from a given table. In this article, I explore the internal workings of the NOLOCK table hint and examine the implications of omitting the WITH keyword. Furthermore, although they seem to be aware of a distinction between NOLOCK and the WITH NOLOCK table hint, they again do not seem to comprehend how the two differ from one another. However, from the interactions that I have had with these esteemed developers it doesn’t seem like they understand how the NOLOCK table hint works. One of my first observations when I joined my current employer is that almost all T-SQL scripts written by application developers uses the NOLOCK table hint. Every once in a while, SQL Server database administrators find themselves in disagreements with their application developer counterparts – particularly when it comes to some of the latter’s Transact SQL (T-SQL) developmental practices.
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