How to check your tables or indexes are in buffer cache

In order to reduce disk I/O and improve performance, add more RAM to your SQL Server machine is the most intuitive idea. However, how can you know your SQL queries get benefit from more RAM? Below SQL query helps you to check the content of the SQL Server buffer cache, it shows you the top 50 objects (tables and indexes) there, by the number of data pages, of the current database.

;WITH memusage_CTE AS (SELECT bd.database_id, bd.file_id, bd.page_id, bd.page_type
, COALESCE(p1.object_id, p2.object_id) AS object_id
, COALESCE(p1.index_id, p2.index_id) AS index_id
, bd.row_count, bd.free_space_in_bytes, CONVERT(TINYINT,bd.is_modified) AS 'DirtyPage'
FROM sys.dm_os_buffer_descriptors AS bd
JOIN sys.allocation_units AS au
ON au.allocation_unit_id = bd.allocation_unit_id
OUTER APPLY (
SELECT TOP(1) p.object_id, p.index_id
FROM sys.partitions AS p
WHERE p.hobt_id = au.container_id AND au.type IN (1, 3)
) AS p1
OUTER APPLY (
SELECT TOP(1) p.object_id, p.index_id
FROM sys.partitions AS p
WHERE p.partition_id = au.container_id AND au.type = 2
) AS p2
WHERE bd.database_id = DB_ID() AND
bd.page_type IN ('DATA_PAGE', 'INDEX_PAGE','TEXT_MIX_PAGE') )
SELECT TOP 50 DB_NAME(database_id) AS 'Database',OBJECT_NAME(object_id,database_id) AS 'Table Name', index_id,COUNT(*) AS 'Pages in Cache', SUM(dirtyPage) AS 'Dirty Pages'
FROM memusage_CTE
GROUP BY database_id, object_id, index_id
ORDER BY COUNT(*) DESC