In my recent training I was asked to how to find which is the busiest database in any SQL Server Instance. What he really meant by this is which database was doing lots of read and write operation.
To find the answer to this question I decided to look into the DMV which contains all the details of the executed query. From the DMV sys.dm_exec_query_stats I found three most important columns to determine busiest database.
DMV sys.dm_exec_query_stats contained columns total_logical_reads, total_logical_writes, sql_handle. Column sql_handle can help to to determine the original query by CROSS JOINing DMF sys.dm_exec_sql_text. From DMF sys.dm_exec_sql_text Database ID and from Database ID can be figured out very quickly.
SELECT SUM(deqs.total_logical_reads) TotalPageReads,
WHEN DB_NAME(dest.dbid) IS NULL THEN 'AdhocSQL'
ELSE DB_NAME(dest.dbid) END Databasename
FROM sys.dm_exec_query_stats deqs
CROSS APPLY sys.dm_exec_sql_text(deqs.sql_handle) AS dest
GROUP BY DB_NAME(dest.dbid)
Reference: Pinal Dave (http://blog.SQLAuthority.com)