Mysql optimizer hint how to#

If you are the developer writing this code, just blame yourself. It is your solemnly sworn duty to do such. Though, query re-write / tune first and then adjust your locking as a last resort.īut as a DBA, always blame the developer's code. When do you know when to use with(rowlock)? When your system isn't letting user play nice with each other in the same table / record. Similar to Using Optimizer Hints to Improve MySQL Query Performance (20) Applied Partitioning And Scaling Your Database System Presentation. If you know the personality of your system on how the data runs through it, you can use with(nolock) to your advantage quite a bit though.

The problem with(nolock) is that you can return the committed record sitting there in the DB already, plus the dirty record that is about to update the sitting record thus a double return of records to your SELECT statement. Sometimes by using with(rowlock), you can get better multi-user (multiple user connections) performance. The task of query optimizer is to determine the most efficient means for executing queries. An INSERT does not matter because it will lock the PAGE automatically.

So, you might see people use with(nolock) on their SELECT statements and the use of with(rowlock) on their UPDATE and DELETE statements. But no one spends that detailed amount of time. If everyone designed there database tables so that everything processed each row at page width - the system would be very fast.

Mysql optimizer hint how to#

This is why people approach that problem by using locking hints. These hints are usually designed to provide suggestions to the MySQL query optimizer for how to efficiently perform a certain query, and arent typically. But SQL server is not multi-user friendly sometimes therefore you may need to incorporate locking methods so you can get your data to flow in and out of the database. SQL Server takes the execution plan that was identified in the optimization step and follows those instructions in order to execute the query. This is the most efficient way for SQL server to process multiple date sets. Once an execution plan is chosen, the query optimizer’s job is complete and we can move to the final step of query processing.