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When to reduce the cxpacket wait type in SQL Server?
Occurs when trying to synchronize the query processor exchange iterator. You may consider lowering the degree of parallelism if contention on this wait type becomes a problem. This is a parallel processing wait type where many threads are used to satisfy the query. Each thread deals with a subset of the data.
Why are my cxpacket wait types so high?
If you have a server that has more than one CPU core, you may experience high values of CXPACKET wait types. This is typically due to queries that run in parallel and the real issue is to understand how different versions of a query can impact CXPACKET waits.
When do you use a cxpacket in a query?
CXPACKET occurs when a parallel operation is created for a task. The query processor may determine that a particular operation can be performed more efficiently by using multiple threads depending on the cost of the query. At the execution time, the query execution portion of the query processor decide what parallelism to use.
How does the cxpacket wait type affect OLTP?
However, in OLTP systems, it could well have a negative impact on performance. CXPACKET wait type occurs when there are threads taking longer to execute than the other threads in that query. The completed threads are left in waiting state until the last thread can complete.
Why is cxpacket waiting for a performance tune?
CXPACKET should not be on your worry-list at the moment. Most of the time it’s the synchronising thread waiting for skewed worker threads to finish. The trouble starts when the optimiser expects the load to be evenly spread over worker threads, but in the actual execution one thread gets to do all the work.
What does it mean when you see cxpacket waits?
What CXPACKET means when you see it is that that thread of a parallel query is waiting for another thread of that query to do something. Just because you see a lot of CXPACKET waits doesn’t mean there’s a problem with the query, it means that there is a problem somewhere else.