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Tuesday, December 29, 2015

Memory is one of the important resources for any database management system and for any IT service in general and controlling this critical resource is one of any DBA major challenges.

Most of database management systems has a parameter or more to define the its share from the total amount of server installed memory, this maintain a hard limit to the DBMS that should not exceed and the rest should be used for the operating system itself “in case that there is no other software installed like web services for example and this–by default–the best practice for a production environment.”

This parameter is very useful for defining a hard limit for the memory the database case use and assign the rest for the OS operations in order to maintain the server performance but it is useless for measuring the amount of memory utilized, this is because the simple fact that this is a static value and in order to measure the memory and its peaks we need another figure to be considered which it the buffer pool utilization.

The buffer pool is the area inside SQL Server memory that used for hosting data and indexes pages for both reading and writing operations and represent about 99% of the total memory of SQL Server, by measuring the buffer pool consumption we can then measure the actual memory utilization for SQL Server instance.
 The below snapshot shows the difference between the SQL Server memory utilization “as a whole” and the buffer pool utilization.

While the red line represent the memory utilization the blue one represents the buffer pool utilization, as we can see the total memory utilization is always the same because it is a static value, while the buffer pool utilization changes by the reading/writing operations activities on the system and that is why we find the utilization during some points reached the total assigned memory and sometimes else it decreased below.

 The next step will be how to collect the memory and buffer pool utilization figures and this will be explained deeply in the next post.


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