Ajay Dwivedi tracks down memory grants:
Very often, specially on mixed workload enviroment where server deals with oltp & olap queries together, concurrent sessions allocated with High Memory Grants cause entire SQL Server workload to suffer.
To detect such a situation, I like to watch my critical metrics dashboards. For example, dashboard Monitoring – Live -All Servers of free SQLMonitor tool highlights all these metrics.
Click through for an example of the dashboard as well as a diagnostic query which helps find high-memory grant queries.