What is SQL Server memory grant feedback loop instability problem?

Memory grant feedback can oscillate allocations when workloads are highly variable.

Memory grant feedback adjusts future query memory based on previous executions. However, in workloads with high variance, this feedback loop can become unstable, oscillating between over-allocation and under-allocation. This leads to inconsistent performance, spills, or wasted memory. SQL Server attempts to stabilize this using dampening mechanisms, but skewed workloads can still cause fluctuation.