Which Performance Monitor counter reflects how long SQL Server expects to retain data in memory?

Page Life Expectancy (PLE) is a critical performance monitor counter that measures the duration that SQL Server expects to retain data pages in memory before they are replaced. It indicates the health of the buffer cache; a higher value typically means that SQL Server can efficiently keep data in memory, which generally leads to better performance due to reduced disk I/O. Essentially, PLE provides insights into how well your SQL Server instance is managing its memory resources in relation to the data workload it is handling.

When PLE is low, it may suggest that the server is under memory pressure, causing the database engine to frequently evict pages from memory, which can adversely affect the performance of queries that rely on those pages being cached. Conversely, a high PLE value suggests that data remains in memory long enough to be reused, allowing for quicker access and better overall performance.

Understanding PLE enables database administrators to make informed decisions regarding memory settings and potential adjustments to optimize SQL Server performance, as it is a direct reflection of the efficiency of memory usage in relation to data access patterns.