How to check how many processes going on Database server?

                Today I am going to share one of the interesting experience.Few days before I was working on one of the release . We was using one DB server it has almost 20 database in it.Out of 20 databases 15 was in use.We was testing one functionality .Normally for that functionality system was taking 10 - 20 sec.We started testing and for that functionality it was taking 10 to 20 minute.We surprised what happened.Again we tried then it has taken  9-10 minute.Again we tested and found it is taking  time more than 20 minute.This is different behavior .we concluded there is no problem in code because it was giving correct result.Then question is what is problem.After further analysis we found there are other databases in server which are in use.It is taking more server resources.Following query was helped us identify root cause.

SELECT [Spid] = session_Id
      , ecid
      , [Database] = DB_NAME(sp.dbid)
      , [User] = nt_username
      , [Status] = er.status
      , [Wait] = wait_type
      , [Individual Query] = SUBSTRING (qt.text,
             er.statement_start_offset/2,
      (CASE WHEN er.statement_end_offset = -1
             THEN LEN(CONVERT(NVARCHAR(MAX), qt.text)) * 2
            ELSE er.statement_end_offset END -
                                er.statement_start_offset)/2)
      ,[Parent Query] = qt.text
      , Program = program_name
      , Hostname
      , nt_domain
      , start_time
    FROM sys.dm_exec_requests er
    INNER JOIN sys.sysprocesses sp ON er.session_id = sp.spid
    CROSS APPLY sys.dm_exec_sql_text(er.sql_handle)as qt
    WHERE session_Id > 50              -- Ignore system spids.
    AND session_Id NOT IN (@@SPID)     -- Ignore this current statement.
    ORDER BY 1, 2

  Above query will tell us how many process are going on server.