Preferably, the most frequently used executable query plans should be retrieved from the procedure cache, thereby saving the need to compile, significantly reducing the utilization of CPU resources, and speeding up the response time of SQL Server queries. Recompiling, which is a CPU-intensive process that may degrade performance, can in certain cases be avoided through sound coding practices.
The Memory Activity pane allows monitoring the SQL Server’s dynamic memory management and ensuring its proper handling of the buffer pool.
Each page of memory used by SQL Server is assigned to one of several cache types. Each cache grows and shrinks in size as required. The main caches are the Buffer Cache, which stores a copy of the SQL Server’s most recently used database pages, and the Procedure Cache, which holds recently compiled query execution plans. Both these cache types should satisfy I/O requests and save the need for physical reads from the disk. The Buffer cache’s efficiency also affects the Page Life Expectancy, another indicator displayed in the SQL Memory pane.
Displays the amount of memory currently allocated to the plan cache (formerly known as procedure cache), a memory area used by SQL Server to hold recently compiled query execution plans stored procedures, triggers, ad hoc SQL, and so on.
A low Plan Cache hit rate may lead to performing extra compilations, thereby degrading SQL Server performance by causing extra CPU load. In a such situation, the Procedure Cache Hit Ratio Alarm is invoked. For details, see .
The plan cache hit rate is the average hit rate for all procedure cache object types, except for ad hoc SQL. This rate is calculated using a differential sampling method, which gauges only the last few sampled periods.
The buffer cache, which is an in-memory copy of recently used database pages, is normally the largest memory cache used by SQL Server. If an SQL process needs to access a database page, finding this page in the buffer cache spares the SQL Server the need to read the page from disk, thereby significantly reducing the amount of disk I/O and speeding up queries.
High buffer cache hit rate indicates that SQL Server efficiently uses the memory allocated to its buffer cache. Low buffer cache hit rate, on the other hand, indicates that SQL Server is finding fewer pages already in memory, resulting in the need to perform more disk reads.
A flow that represents data/index pages written to disk per second. Normally, SQL users do not have to wait for database write operations to complete, as most modifications to database pages are made in the buffer cache.
Physical read operations are necessary when accessing new table or index pages. Nevertheless, these operations should be avoided when possible, as requested pages should reside in the SQL Server buffer cache.
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