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Microsoft® SQL Server 2012 Unleashed by Alex T. Silverstein, Chris Gallelli, Paul T. Bertucci, Ray Rankins

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Shared Query Plans

SQL Server 2012 execution plans consist of two main components: a query plan and an execution context. The query plan is the bulk of the execution plan. Query plans are re-entrant, read-only data structures used by any number of users. There are at most ever only two copies of the query plan in memory: one copy for all serial executions and another for all parallel executions. The parallel copy covers all parallel executions, regardless of their degree of parallelism. When a SQL statement is executed, the Database Engine searches the plan cache to see whether an execution plan for the same SQL statement is already in the plan cache. If a query plan does exist, the Database Engine reuses it, saving the overhead of recompiling ...

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