This document discusses the SQL Server plan cache. It begins with an introduction to the author and then provides three sections: 1. It explains that the plan cache holds each query plan in a subset of the buffer pool. Single-run ad hoc queries may be stored if optimize for ad hoc is enabled. 2. It describes how a query plan is built, including logical and physical processing. The query parser checks syntax and the query optimizer builds the plan to execute the query in minimum time. 3. It outlines ways plans can be flushed from the cache, such as through DBCC commands, statistics updates, or memory pressure. Sample queries are provided to examine the plan cache.