The Query Store is possibly the biggest new engine feature to come with the release of SQL Server 2016. DBAs and developers should be more than familiar with the situation of a query behaving reliably for a long period, which suddenly changed into a slow-running, resource-killing monster. Some readers may identify the cause of the issue as the phenomenon of parameter sniffing or similarly through stale statistics. Either way, when troubleshooting to find out why one unchanging query suddenly becomes slow, knowing the query execution plan(s) that SQL Server has created and used can be very helpful. A major issue when investigating these types of problems is the transient nature of query plans and their execution statistics. This is where Query Store comes into play; SQL Server collects and permanently stores information on query compilation and execution on a per-database basis. This information is then persisted inside each database that is being monitored by the Query Store functionality, allowing a DBA or developer to investigate performance issues after the fact. It is even possible to perform longer term query analysis, providing an insight into how query execution plans change over a longer time frame. This sort of insight was previously only possible via handwritten solutions or third-party monitoring solutions, which may still not allow the same insights as the Query Store does.