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What is Resource_semaphore wait type?
Description: This wait type is when a thread is waiting for a query execution memory grant so it can begin executing. Memory grants are used for performing query operations like sorts and hashes.
What is SQL semaphore?
The Query Memory itself is a limited resource in SQL Server, and is therefore protected by a so-called Resource Semaphore. A semaphore itself is nothing more like a synchronization object that is used to control the access to a shared resource – in our case to the Query Memory.
What is Cmemthread?
CMEMTHREAD indicates there are lots of memory object synchronization to make sure that object accessed by different thread (worker) would not get corrupted. this technique is mostly talked about when Windows Synchronization Object, such as Mutex or CriticalSection topic comes into the picture.
Where does the cxpacket wait type come from?
The SQL Server CXPACKET wait type is one of the most misinterpreted wait stats. The CXPACKET term came from C lass E x change Packet, and in its essence, this can be described as data rows exchanged among two parallel threads that are the part of a single process.
When to stop worrying about CLR _ semaphore wait time?
Stop worrying about timer/queue waits like CLR_SEMAPHORE. These waits always accumulate wait time, but this is not “bad” wait time in 99.999% of all cases. You should be filtering them out of your analysis and focusing on the ones that matter and that you can do anything about anyway.
What does resource semaphore wait type mean in SQL Server?
If query is not able to be granted this requested memory by a Resource Semaphore, then that query will be in a waiting state with a RESOURCE_SEMAPHORE wait type if you query the sysprocesses system table or sys.dm_exec_request DMV. When a Resource Semaphore receives a new request, it first checks if any query is waiting or not.
Why does SQL Server have a high cxpacket wait type?
Another scenario where high values of SQL Server CXPACKET wait type can occur is due to uneven distribution of data across the threads. This is a typical scenario where CXPACKET is not the problem, but that the CXPACKET value is an indicator that a problem exists.