When working with SQL Server, it is common to come across questions about memory usage. One of the most frequently asked questions is why SQL Server takes up all the memory and does not release it. Another common question is how to determine the amount of memory used by databases.

To answer these questions, we need to delve into the topic of memory management in SQL Server. One way to understand the memory usage is by using commands like DBCC MEMORYSTATUS, which provide insights into the internal workings of SQL Server. However, a more interesting approach is to examine the pages in the buffer pool for different databases using Dynamic Management Views (DMVs).

Let’s take a look at an example query that lists the number of pages in the buffer pool by database and page type:

--List the Number of pages in the buffer pool by database and page type
SELECT DB_NAME(database_id), page_type, COUNT(page_id) AS number_pages
FROM sys.dm_os_buffer_descriptors
WHERE database_id != 32767
GROUP BY database_id, page_type
ORDER BY number_pages DESC
GO

The output of this query provides valuable information about the amount of data pages and index pages loaded into the SQL Server memory. By analyzing this data, we can gain insights into the memory usage patterns of our databases.

We can also modify the query to scan the buffer pool based on the type of pages loaded into memory. Here’s an example:

--List the number of pages in the buffer pool by page type
SELECT page_type, COUNT(page_id) AS number_pages
FROM sys.dm_os_buffer_descriptors
GROUP BY page_type
ORDER BY number_pages DESC
GO

--List the number of dirty pages in the buffer pool
SELECT COUNT(page_id) AS number_pages
FROM sys.dm_os_buffer_descriptors
WHERE is_modified = 1
GO

In the above query, we have also included the count of dirty pages, which are pages in memory that have been modified but not yet flushed out. This information can be particularly useful when managing multiple databases on a server and trying to identify memory consumption.

By utilizing these DMVs, we can gain a better understanding of how SQL Server utilizes memory and identify any unusual memory usage patterns in our environment.

Feel free to share your thoughts and observations in the comments section. Have you noticed anything peculiar in your SQL Server memory usage? Let’s discuss!

Reference: Pinal Dave (blog.sqlauthority.com)