8645: A time out occurred while waiting for memory resources to execute the query

What does it mean?

A query timed out while waiting on the resource semaphore for the memory grant it needs to execute. Because memory pressure prevented a grant from being allocated, the operation was canceled.

Why does it happen?

Concurrent memory-intensive queries (large sorts, hash joins, hash aggregates) consumed the entire query memory pool; new queries queued on the semaphore and timed out. Oversized memory grant estimates (stale statistics, bad plans) or insufficient server memory are the root cause.

How to fix it

Identify queries waiting for or holding memory with sys.dm_exec_query_memory_grants and the resource semaphore DMVs. Update statistics and fix plans that cause inflated memory grants (appropriate indexes, better estimates). Reduce the concurrency of memory-intensive queries; if needed, cap memory grants with Resource Governor. Review the server memory configuration (max server memory).