Answer
SQL Server uses a plan cache to store compiled execution plans so that subsequent executions of the same (or parameterized) queries can skip the compilation phase.
Benefits:
- Reduces CPU overhead from repeated compilations.
- Improves response time for frequently executed queries and stored procedures.
Challenges:
- Poorly parameterized or ad-hoc queries can cause plan cache bloat, with many single-use plans.
- Parameter sniffing issues stem from plan reuse across different parameter values.
- Schema changes or statistics updates can invalidate plans, causing recompilation spikes.
Best practice is to use parameterized queries, monitor plan cache size and reuse patterns, and leverage Query Store to manage problematic plans.