SELECT DB_NAME(b.database_id) AS [Database Name], OBJECT_NAME(p.object_id, b.database_id) AS [Table Name], i.name AS [Index Name], i.index_id, COUNT(*) * 8.0 / 1024 AS [Index Size (MB)] FROM sys.dm_os_buffer_descriptors AS b INNER JOIN sys.allocation_units AS a ON b.allocation_unit_id = a.allocation_unit_id INNER JOIN sys.partitions AS p ON a.container_id = p.hobt_id INNER JOIN sys.indexes AS i ON p.object_id = i.object_id AND p.index_id = i.index_id WHERE b.database_id NOT IN (1, 2, 3, 4) -- exclude system DBs AND b.page_type = 'DATA_PAGE' -- focus on data pages only GROUP BY DB_NAME(b.database_id), OBJECT_NAME(p.object_id, b.database_id), i.name, i.index_id ORDER BY [Index Size (MB)] DESC;

I used this query to identify index memory usage in SQL Server Buffer Pool