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Definition between 2 metrics "Physical Reads" [message #532188] Mon, 21 November 2011 04:58 Go to next message
nikko
Messages: 9
Registered: September 2010
Junior Member
Hello

On 10gR2, I cannot find the exact definition of the 2 following metrics :

"Physical Read Total Bytes Per Sec"
and
"Physical Read Bytes Per Sec"


I would want to know what is the difference between them.

PS : i did not find anything in the doc.

Thanks in advance

nikko
Re: Definition between 2 metrics "Physical Reads" [message #532191 is a reply to message #532188] Mon, 21 November 2011 05:20 Go to previous messageGo to next message
Michel Cadot
Messages: 68625
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
Metrics from what?

Regards
Michel
Re: Definition between 2 metrics "Physical Reads" [message #532201 is a reply to message #532191] Mon, 21 November 2011 06:06 Go to previous messageGo to next message
nikko
Messages: 9
Registered: September 2010
Junior Member
Sorry,

I want to extract some metrics from the awr view dba_hist_sysmetric_summary.

Two of these metrics are "Physical Read Total Bytes Per Sec" and "Physical Read Bytes Per Sec".

And i was unable to find in what they differ by sense.

Regards

Re: Definition between 2 metrics "Physical Reads" [message #532208 is a reply to message #532201] Mon, 21 November 2011 06:22 Go to previous message
John Watson
Messages: 8922
Registered: January 2010
Location: Global Village
Senior Member
Hi, Nikko - I've run a few queries, and I think the discrepency may be to do with whether the statistic is accumulated across all sessions or refers only to sessions logged in at any one moment. There also appears to be a difference between reads done by session server processes and by background processes. For instance:
orcl> select * from v$sysstat where lower(name) like '%physical read%bytes';

STATISTIC# NAME                                                                  CLASS      VALUE    STAT_ID
---------- ---------------------------------------------------------------- ---------- ---------- ----------
        50 physical read total bytes                                                 8  310821888 2572010804
        80 physical read bytes                                                       8  149577728  523531786

orcl> select username,sum(value) from v$sesstat natural join v$session
  2  where statistic#=50 group by username;

USERNAME                       SUM(VALUE)
------------------------------ ----------
                                 61323776
JON                              70172672
SYS                              28498944

orcl> select username,sum(value) from v$sesstat natural join v$session
  2  where statistic#=80 group by username;

USERNAME                       SUM(VALUE)
------------------------------ ----------
                                 35127296
JON                              70172672
SYS                               8388608
I'm not at all sure how to interpret this, and would be interested to know anything else you find out. There are of course many other statistics relevant to this.
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