-- source:https://www.mssqltips.com/sqlservertip/2393/determine-sql-server-memory-use-by-database-and-object/
-- Use for a demo/sample purpose only. This query is not built-in to any product.

DECLARE @total_buffer INT;

SELECT @total_buffer = cntr_value
FROM sys.dm_os_performance_counters 
WHERE RTRIM([object_name]) LIKE '%Buffer Manager'
AND counter_name = 'Database Pages';

;WITH src AS
(
SELECT 
database_id, db_buffer_pages = COUNT_BIG(*)
FROM sys.dm_os_buffer_descriptors
--WHERE database_id BETWEEN 5 AND 32766
GROUP BY database_id
)
SELECT TOP 10 
[db_name] = CASE [database_id] WHEN 32767 
THEN 'Resource DB' 
ELSE DB_NAME([database_id]) END,
--db_buffer_pages,
--db_buffer_MB = db_buffer_pages / 128,
db_buffer_percent = CONVERT(DECIMAL(6,3), 
db_buffer_pages * 100.0 / @total_buffer)
FROM src
--ORDER BY db_buffer_MB DESC; 
order by db_buffer_percent DESC;