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OTN Nordic Tour 2013

I got up this morning in plenty of time to get to the airport to fly to Sweden to begin the OTN Nordic Tour 2013 tomorrow. I then proceeded to wait and wait and wait for the taxi. Eventually it did arrive, but now the rush hour traffic had started to build up, so time was ticking by and we were standing still for a very long time. I tweeted that I would probably miss my flight and I really believed I would.

After a considerable amount of time, with me trying to ignore the nervous glances of my driver, the traffic opened up, I got to the airport and check-in was empty, as was security. I got through in time to grab a drink on the way to boarding. Phew…

OTN Nordic Tour 2013

I’ll be representing the Oracle ACE Program as part of the OTN Nordic Tour this year. I’ve just booked my flights, so in a little over a week I’ll be starting the three date tour.

  • Oct 22nd : Stockholm, Sweden (ORCAN) – 3 Presentations
  • Oct 23rd : Copenhagen, Denmark (DOUG) – 2 Presentations
  • Oct 24th : Oslo, Norway (OUGN) – 2 Presentations

I put forward a few different papers each event picked different ones, so it looks like I could be presenting up to 6 distinct sessions over the tour. This next week is going to be very busy. I’ve got to put the finishing touches to one presentation, then rehearse all 6 a few times… :)



Hotsos Revisited 2013 – Presentatie materiaal

Hierbij nog dank voor allen die aanwezig waren bij de weer gevulde, informatieve & gezellige avond tijdens “Hotsos Revisited 2013″. Wij presentatoren hebben genoten van het ambiance. Hier ook nog voor degenen die graag het nog een keer willen nalezen het presentatie materiaal van Toon, Jacco, Gerwin, Frits en mij… Presentatie materiaal in alfabetische volgorde: …

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Should you aim to become an Oracle ACE?

I tweeted the following yesterday,

“It’s 7 years ago today that I was made an Oracle ACE. Seriously. It was April Fools Day 2006… :)

The followup from that tweet included a number of questions about what you get out of becoming an Oracle ACE and what is the quickest way to become one. In my mind, these types of questions highlight the misunderstanding of what the Oracle ACE program is. You can hear Vikki, Debra, Alex and myself talking about the Oracle ACE program here, but I feel like I want to clarify a few things. This is just my opinion. Others may say different. :)

Should you aim to become an Oracle ACE?

An inside look at the Oracle ACE program

I was recently part of a 3-part podcast about the ACE program. You can listen to all 3 parts here:

Thanks to Bob Rhubart for the invite and to the other members of the panel (Vikki Lira, Alex Gorbachev and Debra Lilley).




The Oracle XMLDB “anonymous” user account

Trying here to be as correct as possible, as far as I understand it currently.

ANONYMOUS is an Oracle user account specifically designed for HTTP access. It has only one system privilege, that is “create session” and the account is locked by default. If it is unlocked, it only is used for HTTP access via the XDB Protocol Server, aka PL/SQL Gateway, and can access objects in the XDB Repository that are protected by an ACL (Access Control Lists) mentioning this “principal”.

By default there is no ACL file that grants any privilege to this “user” ANONYMOUS. When APEX is installed then there will be a /sys/acls/ro_anonymous_acl.xml file that grants read access to the /images/ or /i/ directory (depending on the APEX version). If you lock ANONYMOUS or remove the ACL defined privileges then APEX can not show/access those files in that XDB Repository folder (/images, /i) if you would need to access these files. For example when using the APEX listener setup the application images and help doc images are stored locally on the server and not in the database, so in principal there is no need to access those image(s) directories in the database.

Example of an ACL which can used by XDB which grants read properties and read content rights to all objects which are protected by this ACL

#66cc66;"><acl description#66cc66;">=#ff0000;">"File /sys/acl/my_acl.xml"
      #66cc66;"><read #66cc66;">-properties#66cc66;">/>
      #66cc66;"><read #66cc66;">-contents#66cc66;">/>
      #66cc66;"><resolve #66cc66;">/>

By default when a resource (a file or folder) is created by a process it will get the privileges defined in the bootstrap ACL (which is protected by itself). So no privileges will be granted to this ANONYMOUS account by default. And even when unlocked, this user only opens up, by default, to hierarchy enabled, XDB Repository related objects. Mind the mentioning “by default”; Its is possible to opening up and overrule default security ruling in place when you alter the content of ACL defaults (which is, could be considered, a security breach). For example you could alter the contents of the bootstrap_acl.xml file in such a way, if your have maliceious intentions from within the database, but you would need very powerful database account access to start with anyway, to make this happen.

Example of the default content of the bootstrap_acl.xml file:

SQL#66cc66;">> #993333; font-weight: bold;">SELECT xdburitype#66cc66;">(#ff0000;">'/sys/acls/bootstrap_acl.xml'#66cc66;">)#66cc66;">.getCLOB#66cc66;">(#66cc66;">) #993333; font-weight: bold;">FROM dual;
#66cc66;"><acl description#66cc66;">=#ff0000;">"Protected:Readable by PUBLIC and all privileges to OWNER" 
      #66cc66;"><all #66cc66;">/>
      #66cc66;"><all #66cc66;">/>
      #66cc66;"><read #66cc66;">-properties#66cc66;">/>
      #66cc66;"><read #66cc66;">-contents#66cc66;">/>
      #66cc66;"><read #66cc66;">-acl#66cc66;">/>
      #66cc66;"><resolve #66cc66;">/>

Be aware that, although the PUBLIC ACE (Access Control Entries) entry sounds dangerous, this only means that from within the database DIRECT access to the objects via database accounts are possible. This is not possible via HTTP (by default). An example to this effect would be that for the APEX /images directory, which is protected only for read only access of the principal ANONYMOUS, this means that PL/SQL packages (owned/executed by users from WITHIN the database) etc, will not have access to these image files.

The “service” provided via the XDB Protocol Server and its access rules are defined in the xdbconfig.xml configuration file. The services defined there (for example APEX’s entries via PL/SQL, that is, via the PL/SQL gateway) in this xdbconfig.xml file links up to the to be used “principal” (ANONYMOUS in the case of APEX) security access owner, role, trusted user or LDAP definition, for that specific service.

Normally an anonymous user is a user whose credentials have not been validated (hence unauthenticated) that is permitted access to only unprotected resources, but by default all created objects in the XDB repository will be protected by the default bootstrap ACL and in normal cases a ACL with a defined ANONYMOUS principal is not created, does not exist in the database. Even if, you would still need entries in the xdbconfig.xml file that link the (unlocked) ANONYMOUS account with a defined service that grants you access or an entry point to the database.

The underlying by Oracle implemented security mechanism is the same as for the database and also it used the advanced security feature VPD. Due to the fact that Oracle itself makes use of this, a extra license is not needed for this advanced security feature, as long as you don’t use it yourself. Oracle XMLDB in itself is a “no cost option” that comes along when you buy the licenses needed for your database software.

This is a backup copy of a XMLDB OTN Forum Thread.

Congratulations to Yury Velikanov, now an Oracle ACE!

I’m very excited to announce this somewhat old news — we have a brand new Oracle ACE at Pythian — Yury Velikanov. Fantastic addition to Pythian’s team of ACEs and ACE Directors — Fahd Mirza, Gwen Shapira, Jared Still, Christo Kutrovsky and myself. If you want to know more about Oracle ACE Program, the latest issue of Oracle Magazine has an article written by the fellow Oracle ACE Mike Riley — Everything Is Coming Up ACEs!.

I’ve known Yury for a while as I met him online on Oracle-L many years ago. The world is small and after living on different continents (North America and Europe), providence put us together on the third continent — Australia. As I was building our Australian business in Sydney, it took me a year to convince Yury to join Pythian. But I tell you it was worth the efforts!

Yury is one of our top Senior Oracle Apps DBAs and he is also extremely capable when it comes to Oracle core database technology and middleware which you would expect from a very good Apps DBA. A decade ago, Yury was already fusing Oracle E-Business Suite with Oracle RAC when most people couldn’t even afford to think about it. In 2003, Yury became one of the first five Oracle Certified Masters in Europe. In other words, Yury is very talented individual with top notch Oracle EBS and Oracle database skills.

As you probably know, excellent technical skills are not the only required quality of an Oracle ACE. Oracle ACEs are distinguished for their contributions to the community and Yury has always been an enthusiastic Oracle expert willing to both share his knowledge and learn from others. As a result, he is an active contributor to Oracle community, regionally and globally.

Yury founded Oracle e-Business Suite related mailing list several years ago to help Oracle Apps DBAs around the world exchange their experiences and help others. In Australia, Yury has become an organizer of the Sydney Oracle Meetup – an informal group of Oracle professionals meeting regularly face to face.

Yury also has a long list of conferences he presented at including Hotsos Symposium, UKOUG, AUSOUG and others. Recently, Yury has also started blogging on Pythian Blog and is planning to do more and more.

I would like to note that Yury is a person who never refuse to help — he will lose sleep, work 42 hours per day if need but won’t step away if asked for help. I’ve been there myself and I know that he is a very approachable individual and will do whatever it takes.

After all this, how could I not nominate him as an Oracle ACE? Right. There was no way! Now few months late Yury is happily joined our Oracle ACE Team at Pythian. It’s actually happened a few weeks ago, it just took me so long to write about it!

Congrats to Fahd Mirza on becoming an Oracle ACE

Last week brought great news to Pythian — one of our DBAs in Pakistan, Fahd Mirza, has become an Oracle ACE. Fahd joined Pythian in September 2010 as the very first Pythian employee in Pakistan and thanks to his skills and ambitions ended up on the team supporting Exadata environments. Fahd is a long standing active community member, frequent blogger and passionate Oracle technologist evangelizing for Oracle technology in Pakistan. No wonder he got nominated as an Oracle ACE and was accepted.

I should also mention that another Oracle ACE DBA joined us recently Jared Still. Jared is a well respected member of Oracle community, member of the OakTable Network and a veteran of the Oracle-L mailing list. Jared is a top notch Oracle DBA and huge fan of the most popular programming language at Pythian — Perl — and event wrote a book “Perl for Oracle DBAs“.

With all this, we have 5 Oracle ACEs & ACE Directors at Pythian now including Gwen Shapira, Christo Kutrovsky and myself. But that’s not all, Pythian is known as an incubator for Oracle ACEs (I think we were called the Oracle ACE Factory in one of the Oracle ACE newsletters) and it’s been a pleasure to have worked side by side with other Oracle ACEs and ACE Directors — Riyaj Shamsudeen, Doug Burns, Sheeri Cabral and Dmitri Volkov. Some of them became Oracle ACEs at Pythian, some before or after that and even though they are not working at Pythian now, they are still our good friends and help us out on many occasions with training or collaborating on exciting projects.

It’s a great initiative by Oracle through the Oracle ACE program to recognize active community contributors and passionate Oracle professionals around the globe! Well done Oracle!

OOW 2010 Session Stats with Confidence

Thank you very much to all those who attended my session "Stats with Confidence". Unfortunately I was delayed by the keynote running late. With the big party coming up, I appreciate the spirit of those brave souls who stayed back. The late start didn't allow me to show the demo completely. But here are the scripts; hope you will be able to follow it along and run it on your own infrastructure.

It contains the presentation as well. Thanks for attending and hope you will find it useful.

A Tool to Enable Stats Collection for Future Sessions for Application Profiling

The other day I was putting together my presentation for Oracle Open World on Application Profiling in RAC. I was going to describe a methodology for putting a face to an app by measuring how it behaves in a database – a sort of a signature of that application. I was going to use the now-ubiquitous 10046 trace for wait events and other activities inside the database. For resource consumption such as redo generated, logical I/Os, etc., I used the v$sesstat; but then I was stuck. How would I collect the stats of a session when the session has not even started and I don’t know the SID. That problem led to the development of this tool where the stats of a future session can be recorded based on some identifying factors such as username, module, etc. Hope this helps in your performance management efforts.

The Problem

Suppose you want to find out the resource consumed by a session. The resources could be redo generation, CPU used, logical I/O, undo records generated – the list is endless. This is required for a lot of things. Consider a case where you want to find out which apps are generating the most redo; you would issue a query like this:

select sid, value
from v$sesstat s, v$statname n
where n.statistic# = s.statistic#
and = 'redo size'

The value column will show the redo generated. From the SID you can identify the session. Your next stop is v$session to get the other relevant information such as username, module, authentication scheme, etc. Problem solved, right?

Not so fast. Look at the above query; it selects from v$sesstat. When the session is disconnected, the stats disappear, making the entries for that session go from v$sesstat. If you run the query, you will not find these sessions. You have to constantly select from the v$sesstat view to capture the stats of the sessions hoping that you would capture the stats before the session disconnects. But it will be not be guaranteed. Some short sessions will be missed in between collection samples. Even if you are lucky to capture some stats of a short session, the other relevant information from v$session will be gone.

Oracle provides a package dbms_monitor, where a procedure named client_id_stat_enable allows you to enable stats collection on a future session where the client_id matches a specific value, e.g. CLIENT1. Here is an example:

execute dbms_monitor.client_id_stat_enable('CLIENT1');

However there are three issues:

(1) It collects only about 27 stats, out of 400+

(2) It offers only three choices for selecting sessions – client_id, module_name and service_name.

(3) It aggregate them, sums up all stats for a specific client_id. That is pretty much useless without a detailed session level.

So, in short, I didn’t have a readily available solution.


Well, necessity is the mother of invention. When you can’t find a decent tool; you build it; and so did I. I built this tool to capture the stats. This is version 1 of the tool. It has some limitations, as shown at the end. These limitations do not apply to all situations; so the tool may be useful in a majority of the cases. Later I will expand the tool to overcome these limitations.


The fundamental problem, as you recall, is not the dearth of data (v$sesstat has plenty); it’s the sessions in the future. To capture those sessions, the tool relies on a post-logon database trigger to capture the values.

The second problem was persistence. V$SESSTAT is a dynamic performance view, which means the records of the session will be gone when the session disappears. So, the tool relies on a table to store the data.

The third problem is the getting the values at the very end of the session. The difference between the values captured at the end and beginning of the session are the stats. To capture the values at the very end; not anytime before, the tool relies on a pre-logoff database trigger.

The fourth challenge is identification of sessions. SID of a session is not unique; it can be reused for a new session; it will definitely be reused when the database is recycled. So, the tool uses a column named CAPTURE_ID, a sequentially incremented number for each capture. Since we capture once at the beginning and then at the end, I must use the same capture_id. I use a package variable to store that capture_Id.

Finally, the tool allows you to enable stats collections based on some session attributes such as username, client_id, module, service_name, etc. For instance you may want to enable stats for any session where the username = ‘SCOTT’ or where the os_user is ‘ananda’, etc. These preferences are stored in a table reserved for that purpose.


Now that you understand how the tool is structured, let me show the actual code and scripts to create the tool.

(1) First, we should create the table that holds the preferences. Let’s call this table RECSTATS_ENABLED. This table holds all the different sessions attributes (ip address, username, module, etc.) that can enable stats collection in a session.


If you want to enable stats collection of a session based on a session attribute, insert a record into this table with the session attribute and the value. Here are some examples. I want to collect stats on all sessions where client_info matches ‘MY_CLIENT_INFO1’. You would insert a record like this:

insert into recstats_enabled values ('CLIENT_INFO','MY_CLIENT_INFO1');

Here are some more examples. All sessions where ACTION is ‘MY_ACTION1’:

insert into recstats_enabled values ('ACTION','MY_ACTION1');

Those of user SCOTT:

insert into recstats_enabled values ('SESSION_USER','SCOTT')

Those with service name APP:

insert into recstats_enabled values ('SERVICE_NAME','APP')

You can insert as many preferences as you want. You can even insert multiple values of a specific attribute. For instance, to enable stats on sessions with service names APP1 and APP2, insert two records.

Important: the session attribute names follow the naming convention of the USERENV context used in SYS_CONTEXT function.

(2) Next, we will create a table to hold the statistics


Note, I used the tablespace USERS; because I don’t want this table, which can potentially grow to huge size, to overwhelm the system tablespace. The STATISTIC_NAME and STATISTIC_VALUE columns record the stats collected. The other columns record the other relevant data from the sessions. All the attributes here have been shown with VARCHAR2(2000) for simplicity; of course they don’t need that much of space. In the future versions, I will put a more meaningful limit; but 2000 does not hurt as it is varchar2.

The capture point will show when the values were captured – START or END of the session.

(3) We will also need a sequence to identify the sessions. Each session will have 400+ stats; we will have a set at the end and once at the beginning. We could choose SID as an identifier; but SIDs could be reused. So, we need something that is truly unique – a sequence number. This will be recorded in the CAPTURE_ID column in the stats table.

SQL> create sequence seq_recstats;

(4) To store the capture ID when the post-logon trigger is fired, to be used inside the pre-logoff trigger, we must use a variable that would be visible to entire session. A package variable is the best for that.

create or replace package pkg_recstats
g_recstats_id number;

(5) Finally, we will go on to the meat of the tool – the triggers. First, the post-logon trigger to capture the stats in the beginning of the session:

CREATE OR REPLACE TRIGGER SYS.tr_post_logon_recstats
after logon on database
l_stmt varchar2(32000);
l_attr_val recstats_enabled.attribute_value%TYPE;
l_capture_point recstats.capture_point%type := 'START';
l_matched boolean := FALSE;
pkg_recstats.g_recstats_id := null;
for r in (
select session_attribute, attribute_value
from recstats_enabled
order by session_attribute
exit when l_matched;
-- we select the userenv; but the null values may cause
-- problems in matching; so let’s use a value for NVL
-- that will never be used - !_!_!
l_stmt := 'select nvl(sys_context(''USERENV'','''||
r.session_attribute||'''),''!_!_!_!'') from dual';
execute immediate l_stmt into l_attr_val;
if l_attr_val = r.attribute_value then
-- match; we should record the stats
-- and exit the loop; since stats should
-- be recorded only for one match.
l_matched := TRUE;
select seq_recstats.nextval
into pkg_recstats.g_recstats_id
from dual;
insert into recstats
from v$mystat s, v$statname n
where s.statistic# = n.statistic#;
end if;
end loop;

The code is self explanatory. I have provided more explanation as comments where needed.

(6) Next, the pre-logoff trigger to capture the stats at the end of the session:

CREATE OR REPLACE TRIGGER SYS.tr_pre_logoff_recstats
before logoff on database
l_capture_point recstats.capture_point%type := 'END';
if (pkg_recstats.g_recstats_id is not null) then
insert into recstats
from v$mystat s, v$statname n
where s.statistic# = n.statistic#;
end if;

Again the code is self explanatory. We capture the stats only of the global capture ID has been set by the post-logoff trigger. If we didn’t do that all the sessions would have started recording stats at their completion.


Now that the setup is complete, let’s perform a test by connecting as a user with the service name APP:

SQL> connect arup/arup@app

In this session, perform some actions that will generate a lot of activity. The following SQL will do nicely:

SQL> create table t as select * from all_objects;

SQL> exit

Now check the RECSTATS table to see the stats on this catured_id, which happens to be 1330.

col name format a60
col value format 999,999,999
select a.statistic_name name, b.statistic_value - a.statistic_value value
from recstats a, recstats b
where a.capture_id = 1330
and a.capture_id = b.capture_id
and a.statistic_name = b.statistic_name
and a.capture_point = 'START'
and b.capture_point = 'END'
and (b.statistic_value - a.statistic_value) != 0
order by 2

Here is the output:

NAME                                                                VALUE
------------------------------------------------------------ ------------
workarea memory allocated -2
change write time 1
parse time cpu 1
table scans (long tables) 1
cursor authentications 1
sorts (memory) 1
user commits 2
opened cursors current 2
IMU Flushes 2
index scans kdiixs1 2
parse count (hard) 2
workarea executions - optimal 2
redo synch writes 2
redo synch time 3
rows fetched via callback 5
table fetch by rowid 5
parse time elapsed 5
recursive cpu usage 8
switch current to new buffer 10
cluster key scan block gets 10
cluster key scans 10
deferred (CURRENT) block cleanout applications 10
Heap Segment Array Updates 10
table scans (short tables) 12
messages sent 13
index fetch by key 15
physical read total multi block requests 15
SQL*Net roundtrips to/from client 18
session cursor cache hits 19
session cursor cache count 19
user calls 25
CPU used by this session 28
CPU used when call started 29
buffer is not pinned count 33
execute count 34
parse count (total) 35
opened cursors cumulative 36
physical read total IO requests 39
physical read IO requests 39
calls to get snapshot scn: kcmgss 45
non-idle wait count 67
user I/O wait time 116
non-idle wait time 120
redo ordering marks 120
calls to kcmgas 143
enqueue releases 144
enqueue requests 144
DB time 149
hot buffers moved to head of LRU 270
recursive calls 349
active txn count during cleanout 842
cleanout - number of ktugct calls 842
consistent gets - examination 879
IMU undo allocation size 968
physical reads cache prefetch 997
physical reads 1,036
physical reads cache 1,036
table scan blocks gotten 1,048
commit cleanouts 1,048
commit cleanouts successfully completed 1,048
no work - consistent read gets 1,060
redo subscn max counts 1,124
Heap Segment Array Inserts 1,905
calls to kcmgcs 2,149
consistent gets from cache (fastpath) 2,153
free buffer requested 2,182
free buffer inspected 2,244
HSC Heap Segment Block Changes 2,519
db block gets from cache (fastpath) 2,522
consistent gets 3,067
consistent gets from cache 3,067
bytes received via SQL*Net from client 3,284
bytes sent via SQL*Net to client 5,589
redo entries 6,448
db block changes 9,150
db block gets 10,194
db block gets from cache 10,194
session logical reads 13,261
IMU Redo allocation size 16,076
table scan rows gotten 72,291
session uga memory 88,264
session pga memory 131,072
session uga memory max 168,956
undo change vector size 318,640
session pga memory max 589,824
physical read total bytes 8,486,912
cell physical IO interconnect bytes 8,486,912
physical read bytes 8,486,912
redo size 8,677,104

This clearly shows you all the stats of that session. Of course the table recorded all other details of the session as well – such as username, client_id, etc., which are useful later for more detailed analysis. You can perform aggregations as well now. Here is an example of the stats collected for redo size:

select session_user, sum(STATISTIC_VALUE) STVAL
from recstats
where STATISTIC_NAME = 'redo size'
group by session_user


------------ ---------
ARUP 278616
APEX 4589343
… and so on …

You can disassemble the aggregates to several attributes as well. Here is an example where you want to find out the redo generated from different users coming from different client machines

select session_user, host, sum(STATISTIC_VALUE) stval
from recstats
where STATISTIC_NAME = 'redo size'
group by session_user, host


------------ ----------- -------
ARUP oradba2 12356
ARUP oradba1 264567
APEX oradba2 34567
… and so on …

Granularity like this shows you how the application from different client servers helped; not just usernames.


As I mentioned, there are some limitations you should be aware of. I will address them in the next iterations of the tool. These are not serious and applicable in only certain cases. As long as you don’t encounter that case, you should be fine.

(1) The logoff trigger does not fire when the user exits from the session ungracefully, such as closing down the SQL*Plus window, or closing the program before exiting. In such cases the stats at the end of the session will not be recorded. In most application infrastructure it does not happen; but it could happen for adhoc user sessions such as people connecting through TOAD.

(2) The session attributes such as module, client_id and action can be altered within the session. If that is the case, this tool does not record that fact since there is no triggering event. The logoff trigger records the module, action and client_id set at that time. These attributes are not usually changed in application code; so it may not apply to your case.

(3) Parallel Query sessions will have a special issue since there will be no logoff trigger. So in case of parallel queries, you will not see any differential stats. If you don’t use PQ, as most OLTP applications do, you will not be affected.

(4) If the session just sits there without disconnecting, the logoff trigger will never fire and the stats will never be captured. Of course, it will be eventually captured when the session exits.

Once again, these limitations apply only to certain occasions. As long as you are aware of these caveats, you will be able to use this tool to profile many of your applications.

Happy Profiling!