PURPOSE
-------
To explain the reason why global cache timings are 0 in v$sysstat
even if TIMED_STATISTICS=TRUE in a RAC instance on Tru64 unix.

SCOPE & APPLICATION
-------------------
All users working on RAC on Tru64 unix.

Global cache timings are always 0 in v$sysstat on Tru64 Unix
------------------------------------------------------------

Problem specification
---------------------
All global cache timings in v$sysstat remain 0 in Real Application Cluster 
on Tru64 Unix, no matter how much Cache Fusion traffic has occurred. The 
TIMED_STATISTICS parameter in init.ora is also set to TRUE.

The output of the query on v$sysstat will be like :


SQL> select name,value from v$sysstat where name like 'global cache%time%'; 
NAME                                                                  VALUE 
---------------------------------------------------------------- ---------- 
global cache get time                                                     0 
global cache convert time                                                 0 
global cache cr block receive time                                        0 
global cache current block receive time                                   0 
global cache cr block build time                                          0 
global cache cr block flush time                                          0 
global cache cr block send time                                           0 
global cache current block pin time                                       0 
global cache current block flush time                                     0 
global cache current block send time                                      0 
global cache convert timeouts                                             0 

Solution
--------
Check whether the file /dev/timedev exists. The global cache timings are 0 
because this file is missing. The solution is to create the file 
/dev/timedev 

Explanation
-----------
The profiler code on Tru64 makes use of the global time information set in 
the system special file - /dev/timedev - This file holds a global time which 
reports time with millisecond granularity. Hence when the profiling code calls 
a port specific function to get the time, this function looks at /dev/timedev 
which doesn't exist. This results in a failure return status, which ends
in 0 being returned to the profiling code for a timestamp. 

To create /dev/timedev 
---------------------- 
The /dev/timedev inode is a mechanism used to access the system real-time clock 
To provide a low latency pathway to the system clock, this mechanism maps it 
directly to the process space. Login as root and create this inode in the /dev 
directory: 

* mknod /dev/timedev c 15 0 
* chmod +r /dev/timedev 

After creating /dev/timedev file, the global cache timings will reflect the
statistics as follows:

SQL> select name,value from v$sysstat where name like '%cr block%'; 

NAME                                                                  VALUE 
---------------------------------------------------------------- ---------- 
global cache cr blocks received                                        3082 
global cache cr block receive time                                     1694 
global cache cr blocks served                                          3076 
global cache cr block build time                                        135 
global cache cr block flush time                                       1126 
global cache cr block send time                                          73 

RELATED DOCUMENTS
-----------------
Note that this is also documented in Appendix C 'Tuning for Oracle9i on Tru64'
of Oracle9i Administrator's Reference Release for UNIX Systems.