![]() When the buffer manager writes to a page in memory, the page becomes “dirty.” Dirty pages are flushed to disk at regular intervals, allowing most work to take place in memory and making costlier disk operations less frequent. ![]() The buffer manager handles queries by checking first for pages within the buffer cache and, if they’re absent, pulling them from disk. Whether on disk or in the buffer cache, SQL Server stores data within eight-kilobyte pages. Rather than reading and writing to disk directly, SQL Server uses a buffer manager, which moves data between storage and an in-memory buffer cache. In a sense, a “query” in SQL Server is a batch of one or more T-SQL statements compiled and run as an execution plan. When a user executes a batch, SQL Server first searches its cache for the execution plan, and compiles a new one if it comes up short.Īs SQL Server compiles your batches, it optimizes them, measuring statistics like the number of rows involved and adjusting the execution plan in response. For software that queries SQL Server (e.g., the sqlcmd CLI or SQL Server Management Studio), the keyword GO indicates the end of the batch.Įvery batch is compiled and cached in memory as an execution plan, a set of data structures that allow SQL Server to reuse a batch in multiple contexts, with different users and parameters. ![]() For example, you might write a batch to return a result set from a SELECT statement, then use the result set to perform another operation. It is up to you to determine the order of statements within a batch. With T-SQL, you can write batches, groups of statements that perform a series of related operations on a database, and that SQL Server can compile into a single, streamlined query. We’ll start with an overview of how SQL Server works. In this post, we’ll explore the metrics that provide visibility into SQL Server’s functionality, from data persistence to query optimization, indexes, and resource pooling.
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