What is cxpacket wait

You should consider tuning such queries. If tuning the query is not an option, either through code or index modifications, consider the following options:. Setting the max degree of parallelism for the instance will be overridden by the use of the MAXDOP query hint, should both be used at the same time.

If a guaranteed degree of parallelism is required for a specific query or set of queries then one may consider the use of Resource Governor to set the degree of parallelism for a workload group. It makes me think that there are no SQL specialists in Confio and casts doubt on the quality of the products. I did a quick google search on tuning cxpacket wait types.

As we might notice the CPU time is very close to elapsed time. The query is CPU bound; if not execute the query again to make sure we are reading the data from cache.

This example is to understand parallel query execution, not disk IO, so we need to get the data in the cache before we can continue. On the execution plan, right click on Cluster Index Seek and click on Properties as shown below. Notice the CPU time and elapsed time. If you take a look at the execution plan, we can see that not all threads processed , rows. Some threads processed , rows, some , rows, and some none.

Finally we can see that in the above query, all threads are processing rows, leading to low elapsed time. In all the above examples, join, subquery and IN, when handling 4 rows from a temporary table you will see the elapsed time to be less than with an IN clause. This does not mean that an IN clause is always better. Thanks for sharing this wonderfull article. Very hard to give detailed advice without looking at the query in more depth I'm afraid. HI Paul, Thank you for the reply.

Do you see any issue going with this way. Just trying to know more about this method. Featured Author Paul White is an independent SQL Server consultant specializing in performance tuning, execution plans, and the query optimizer.

Unexpected parallelism? There are a variety of causes of unexpected table scans, including: Missing nonclustered index so a table scan is the only alternative Out-of-date statistics so the Query Optimizer thinks a table scan is the best data access method to use An implicit conversion, because of a data type mismatch between a table column and a variable or parameter, which means a nonclustered index cannot be used Arithmetic being performed on a table column instead of a variable or parameter, which means a nonclustered index cannot be used In all these cases, the solution is dictated by what you find the root cause to be.

As far as general wait statistics are concerned, you can find more information about using them for performance troubleshooting in: My SQLskills blog post series, starting with Wait statistics, or please tell me where it hurts My Wait Types and Latch Classes library here My Pluralsight online training course SQL Server: Performance Troubleshooting Using Wait Statistics SQL Sentry Performance Advisor In the next article in the series, I'll discuss skewed parallelism and give you a simple way to see it happening.

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