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Don Burleson Blog 







Quickly find Oracle Session hogs

Oracle Tips by Burleson Consulting
Don Burleson

If the complaint of poor performance is current, then the connected sessions are one of the first things to check to see which users are impacting the system in undesirable ways.  There are a couple of different avenues to take here.

First, you can get an idea of the percentage that each session is/has taken up with respect to I/O.  One rule of thumb is that if any session is currently consuming 50% or more of the total I/O, then that session and its SQL need to be investigated further to determine what activity it is engaged in. 

If you are a DBA that is just concerned with physical I/O, then the physpctio.sql  query will provide the information you need:

This script queries the sys.v_$statname, sys.v_$sesstat, sys.v_$session, and sys.v_$bgprocess views.

   round(100 * total_user_io/total_io,2) tot_io_pct
     b.sid sid,
     nvl(b.username, username,
     sum(value) total_user_io
     sys.v_$statname c, 
     sys.v_$sesstat a,
     sys.v_$session b,
     sys.v_$bgprocess p
   see code depot for full script
      a.statistic#=c.statistic# and
      p.paddr (+) = b.paddr and
      b.sid=a.sid and in ('physical reads',
                 'physical writes',
                 'physical writes direct',
                 'physical reads direct',
                 'physical writes direct (lob)',
                 'physical reads direct (lob)')
group by
      b.sid, nvl(b.username,,
      sum(value) total_io
      sys.v_$statname c,
      sys.v_$sesstat a
      a.statistic#=c.statistic# and in ('physical reads',
                 'physical writes',
                 'physical writes direct',
                 'physical reads direct',
                 'physical writes direct (lob)',
                 'physical reads direct (lob)'))
order by
      3 desc;

If you are a DBA that wants to see the total I/O picture (in other words, both logical and physical I/O), then use the totpctio.sql  query instead:

The complete listing of the totpctio.sql  query can be obtained from the online Code Depot This script also queries the sys.v_$statname, sys.v_$sesstat, sys.v_$session, and sys.v_$bgprocess views.

Regardless of which query you use, the output might resemble something like the following:



9      USR1              71.26

20     SYS               15.76

5      SMON               7.11

2      DBWR               4.28

12     SYS                1.42

6      RECO                .12

7      SNP0                .01

10     SNP3                .01

11     SNP4                .01

8      SNP1                .01

1      PMON                  0

3      ARCH                  0

4      LGWR                  0

In the above example, a DBA would be prudent to examine the USR1 session to see what SQL calls they are making.  You can see that the above queries are excellent weapons that you can use to quickly pinpoint problem I/O sessions.

The Ion tool is the easiest way to analyze AWR disk I/O in Oracle and Ion allows you to spot session hogs.


Mike Ault, one of the world's most widely-read Oracle experts, has finally consented to release his complete collection of more than 450 Oracle scripts.

Mike has priced his collection of 465 scripts at $39.95, less than a dime per script.  You can download them immediately at this link:

If you're a DBA who's looking for real world Oracle tuning techniques, Oracle scripts, and advice on how to get to the heart of critical Oracle performance problems, then you've come to the right place.

Oracle Performance Troubleshooting: With Dictionary Internals SQL & Tuning Scripts was written by one the world's most widely-read DBAs and Oracle internals experts. Robin Schumacher focuses his incredible knowledge of the Oracle data dictionary into a superb book that shows how to quickly troubleshoot and correct Oracle performance problems. 

Plus! The online code depot is available immediately!


   Don Burleson



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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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