Home » RDBMS Server » Performance Tuning » v$sess_io info is not changing. (oracle 9.2.0.8)
v$sess_io info is not changing. [message #349409] Sun, 21 September 2008 10:01 Go to next message
shrinika
Messages: 267
Registered: April 2008
Senior Member
Dear all,

My understanding is, v$sess_io contains one record for each session. The record contains
values for CONSISTENT_GETS,DB_BLOCK_READS are always for the latest query in the seesion.

In my database, i have only one session for username = 'SCOTT'.

scott@DB1.US.ORACLE.COM> select count(*) from emp1;

  COUNT(*)
----------
  13762560

scott@DB1.US.ORACLE.COM> 
SQL> ;
  1  select consistent_gets,physical_reads from v$sess_io
  2* where sid in(select sid from v$session where username='SCOTT')
SQL> /

CONSISTENT_GETS PHYSICAL_READS
--------------- --------------
         255718         161831

SQL> 


The above consistent_gets,physical_reads are reasonable for selecting huge number of records in emp1 table.


Now i run the another query which has only 14 records.

scott@DB1.US.ORACLE.COM> select count(*) from emp;

  COUNT(*)
----------
        14

scott@DB1.US.ORACLE.COM> 
SQL> ;
  1  select consistent_gets,physical_reads from v$sess_io
  2* where sid in(select sid from v$session where username='SCOTT')
SQL> /

CONSISTENT_GETS PHYSICAL_READS
--------------- --------------
         255721         161832

SQL> 


Now the consistent_gets/physical_reads are slightly changed. But this count is very high for selecting only 14 records.

Can any one please explain me on this?

Thanks.

Re: v$sess_io info is not changing. [message #349416 is a reply to message #349409] Sun, 21 September 2008 11:44 Go to previous messageGo to next message
Michel Cadot
Messages: 64152
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
It is the sum up of your whole session. So for the last query (actually the 2 last ones) you have 1 physical read and 3 gets, not so much.

Regards
Michel
Re: v$sess_io info is not changing. [message #349695 is a reply to message #349416] Mon, 22 September 2008 14:17 Go to previous message
shrinika
Messages: 267
Registered: April 2008
Senior Member
Thanks for the clarification Michel!.
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