RESOURCE_SEMAPHORE

This wait occurs when memory can’t be granted to allow query execution, or a process is waiting while query optimization takes place. The most likely cause is an excessive amount of memory requests or concurrent processes. This can also be common in Decision Support or Data Warehousing environments, where large queries involving memory-intensive operations such as sorts and hash joins typically occur.

Sorts and hash joins rely on grants to reserve temporary space in memory before they actually use it. It’s resource semaphore’s job to manage memory grant requests and keep within the server memory limit. If there’s not enough free memory, the query is put into the waiting queue.

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