Category Archives: eBS

Create View and Datatypes

How easy it is to forget!

On creating a view with a literal (alphanumeric) value, Oracle will use the CHAR datatype.

 SQL> create table t1 (id number, val varchar2(20));

Table created.

SQL> create view v1 as select id, val, 'Tweedle' dum from t1;

View created.

SQL> desc v1;

Name Null? Type

--------- -------- -----------------

ID                   NUMBER

VAL                VARCHAR2(20)

DUM             CHAR(7)


This is no problem, since the value is a constant. But what if we mix the datatypes?

SQL> create view v2 as select id, val, 'Doodle' dum from t1;

View created.

SQL> desc v2;
Name Null? Type
--------- -------- ---------------

ID                    NUMBER
VAL                 VARCHAR2(20)
DUM               CHAR(6)

SQL> create view v3 as select * from v1 union select * from v2;

View created.

SQL> desc v3;
Name Null? Type
--------- -------- ---------------

ID                   NUMBER
VAL                VARCHAR2(20)
DUM              VARCHAR2(7)

Oracle automagically changed the datatype to VARCHAR2. (This is also documented in the SQL Reference for UNION (ALL). But it can still lead to some funny results:

SQL> create table t2 (val char(7));

Table created.

SQL> insert into t2 values ('Doodle');

1 row created.

SQL> select * From v3 where dum in (select val from t2);

no rows selected

SQL> select * From v2 where dum in (select val from t2);

---------- -------------------- ------
1 Test Doodle

SQL> select val||'x' from t2;

Doodle x

Never a dull moment with Oracle and creative developers 🙂

FND_GLOBAL.APPS_INITIALIZE: Initialize eBS sessions in SQL and PL/SQL

To access eBS functionality through SQL clients or PL/SQL, it can be necessary to initialize an eBS session.

For example when you need to reference eBS views, access API’s or start concurrent requests from outside eBS.

To initialize an eBS session the API FND_GLOBAL.APPS_INITIALIZE can be used. It has 3 required parameters and 2 optional parameters:
USER_ID -> This is the FND_USER.USER_ID for which is a session is initialized.
RESP_ID -> The FND_RESPONSIBILITY.RESPONSIBILITY_ID that will be used in this session.
SECURITY_GROUP_ID -> An optional SECURITY_GROUP_ID. (Default = 0)
SERVER_ID -> An optional SERVER_ID. (Optional, default = -1)

The SERVER_ID will mostly be used in case of a DMZ or server dependent services.
The APPS_INITIALIZE procedure will accept any numeric value for the parameters. But the session will only be initialized successfully with at least a valid USER_ID.

In this article, we will look at the session initialization through APPS_INITIALIZE. The following steps are executed:
– Set up a PL/SQL table in FND_GLOBAL with some session variables. These variables are accessible through functions in FND_GLOBAL.
– Set up a sys_context (‘FND’) with the same variables.
– Set the organization context.
– Set up the Security Profile in case of HR Security. I will document the details of the HR Security later and skip the details in this article.
– Set the Consumer Resource Group.
– Execute product specific initialization routines.
– Execute the Custom SQL Initialization routine.


In the FND_GLOBAL package body a PL/SQL table is set up to hold session variables. Not all available variables will be set through APPS_INITIALIZE (e.g. CONC_REQUEST_ID that is only set on submitting a concurrent request). And not all variables are available (e.g. CUSTOMER_ID which is derived from the customer field in FND_USER).

Undefined variables are set to -1 for NUMBER values and to NULL for VARCHAR values.

Name Description Remarks
USER_ID User_id from FND_USER Required, not validated
USER_NAME User_name from FND_USER Optional, based on USER_ID
RESP_ID Responsibility_id Optional, not validated
RESP_NAME Responsibility_name Optional, based on RESP_ID
RESP_APPL_ID Resp. application_id Optional, based on RESP_ID
APPLICATION_NAME Resp. application_name Optional, based on RESP_APPL_ID
APPLICATION_SHORT_NAME Resp. application_short_name Optional, based on RESP_APPL_ID
SECURITY_GROUP_ID Security Group ID Optional, validated
PER_BUSINESS_GROUP_ID Business Group ID Derived from Profile Option
PER_SECURITY_PROFILE_ID HR Security Profile Derived from Profile Option
EMPLOYEE_ID User employee_id Optional, from FND_USER
CUSTOMER_ID User customer_id Optional, from FND_USER
SUPPLIER_ID User supplier_id Optional, from FND_USER
SESSION_ID Unique session identifier AUDSID from v$session
SERVER_ID Server_id if entered as param. Optional from FND_NODES
ORG_ID Operating Unit ID Derived from Profile Option
ORG_NAME Operating Unit Name Based on ORG_ID

These variables are also stored in a SYS_CONTEXT with name ‘FND’:

SQL> select FND_GLOBAL.USER_NAME from dual;


SQL> select sys_context('FND','USER_NAME') from dual;



There will however be NO noticeable performance difference between the two. So I advise you to use FND_GLOBAL as it is the documented solution.

Organization Context

The algorithm to derive the Organization Context is as follows.

For pre-R12 environments: Use profile option ‘MO: Operating Unit’ (ORG_ID).

For R12 and beyond, the MOAC structure can be used. First check if profile option ‘MO: Security Profile’ (XLA_MO_SECURITY_PROFILE_LEVEL) is set.
If this profile is set, check profile option ‘MO: Default Operating Unit’ (DEFAULT_ORG_ID).
If DEFAULT_ORG_ID is not set, the ORG_ID will not be initialized.
If XLA_MO_SECURITY_PROFILE_LEVEL is not set, profile option ‘MO: Operating Unit’ (ORG_ID) is used.

The ORG_ID and SECURITY_GROUP_ID are then stored in the sessions CLIENT_INFO. ORG_ID starts at position 1 and is limited to 10 characters. The SECURITY_GROUP_ID starts at position 55.

The CLIENT_INFO is the most common check for eBS database views to verify Organization Context.

Profile Option Cache

After setting the variables, the Profile Option Value cache is initialized. However APPS_INITIALIZE does not set any profile option values yet. It only sets up the required cache (which is also a PL/SQL table).
A number of profile options are used for the initialization, but they are not yet stored in the Profile Option Value cache. In an upcoming article, I’ll go into more detail about the Profile Option Value Cache and the way eBS uses it

Security Context

Then the security context is initialized. The ORG_ID and SECURITY_GROUP_ID are set in the sessions CLIENT_INFO. ORG_ID is stored in the first 10 characters, while SECURITY_GROUP_ID is stored from the 55th position.

Resource Consumer Group

In the profile option ‘FND: Resource Consumer Group’ (FND_RESOURCE_CONSUMER_GROUP) a Resource Consumer Group can be selected. With this setting the database Resource Manager can limit the database resources that the user can use. If this profile option is set, APPS_GLOBAL.APPS_INITIALIZE will alter the session to use the required Resource Consumer Group.

Product Initialization

Individual Oracle Products can execute their own initialization routines. The defined routines are in table FND_PRODUCT_INITIALIZATION. Each initialization can be executed based on specific conditions. These conditions are stored in FND_PRODUCT_INIT_CONDITION.
The setup of these initialization routines is done through the package FND_PRODUCT_INITIALIZATION_PKG. The APPS_INITIALIZE will check the conditions and dependencies on the initialization routines and execute the routines in the required order.

Custom Initialization

You may be aware that you can also set up your own Custom Initialization Routine through the profile option: ‘Initialization SQL Statement – Custom’. If this profile is set, it will also be executed through FND_GLOBAL.APPS_INITIALIZE.

APPS_INITIALIZE has now finished initializing your session. Other eBS software can use the FND_GLOBAL functions, the SYS_CONTEXT or CLIENT_INFO to verify the session and security settings.


P.S. For quick scripts:

eBS Flexfields and Canonical values



Since I have been working a lot on NUMBER and DATE conversions lately, it’s time to write a short note about canonicals.

Oracle eBS Flexfields (and by extension concurrent program parameters) store all values in a VARCHAR2 column. In general it is a bad idea to store NUMBER and DATE in a VARCHAR2 type. See Datatypes and ORA-1722


But for Flexfields we have a controlled environment. Oracle solves problems related to conversions by storing the NUMBER and DATE format as so called ‘canonicals’. This means that all NUMBER and DATE values are stored in a fixed format. It is up tot he application to guarantee that only values in this canonical format are stored in the Flexfields.


Especially for DFF values, they will often be used in customized software units. These customizations are also responsible for keeping the data in the canonical format. Best practice is to use the packages FND_NUMBER and FND_DATE. This will assure that your customizations don’t break when Oracle changes the canonical format. (e.g. change the precision on NUMBER).



The FND_NUMBER package contains 2 procedures: NUMBER_TO_CANONICAL and CANONICAL_TO_NUMBER. Both take 1 parameter which is a NUMBER respectively a VARCHAR2.

The NUMBER canonical format is ‘FM999999999999999999999.99999999999999999999’. Those are 21 positions left and 20 positions right of the decimal ‘.’. Both functions round the result to 20 decimal positions.

For some reason FND development used a TRANSLATE statement to switch between te decimal separator fort he session and the ‘.’ used in the canonical format. (Hint: TO_NUMBER and TO_CHAR (number) accept the parameter ‘nls_numeric_characters’).


SQL> alter session set nls_numeric_characters=',.';

Session altered.

SQL> select fnd_number.number_to_canonical(to_number('12345,12')) from dual;




SQL> select fnd_number.canonical_to_number('12345.12') from dual;




SQL> alter session set nls_numeric_characters='.,';

Session altered.

SQL> select fnd_number.number_to_canonical(to_number('12345.12')) from dual;






The FND_DATE package contains a lot of procedures for backward compatibility. But for canonical values in Flexfields we need CANONICAL_TO_DATE and DATE_TO_CANONICAL.

Since to TO_CHAR(date) and TO_DATE both accept a date mask, the procedure only contain a TO_CHAR/TO_DATE function.

The canonical mask for DATE is: ‘YYYY/MM/DD HH24:MI:SS’.


SQL> alter session set nls_date_format='DD-MON-YYYY HH:MI:SSAM';

Session altered.

SQL> select fnd_date.date_to_canonical(to_date('5-apr-2017 3:21:45PM','dd-mon-yyyy hh:mi:ssam')) from  dual;



2017/04/05 15:21:45

SQL> select fnd_date.canonical_to_date('2017/02/03 21:32:54') from dual;



03-FEB-2017 09:32:54PM


More goodies

Two other functions that are convenient to use when dealing with string values and dates are STRING_TO_DATE and STRING_TO_CANONICAL.

For dates MONTH, AM/PM and AD/BC values are language dependent. So based on the session settings they may return different results. STRING_TO_DATE and STRING_TO_CANONICAL handle this by trying different language settings. In order they try NLS_DATE_FORMAT (default), NLS_NUMERIC_LANGUAGE and the installed eBS languages from FND_LANGUAGES.

Both take a string that represents a date and the date-mask for the string. STRING_TO_DATE returns a DATE value, while STRING_TO_CANONICAL uses STRING_TO_DATE but converts the result to a canonical VARCHAR2.


SQL> alter session set nls_date_language=AMERICAN;

Session altered.

SQL> select nls_language

2  from fnd_languages

3  where installed_flag in ('B','I');





SQL> select to_date('3-mrt-2017 23:45:12','dd-mon-yyyy hh24:mi:ss') from dual;

select to_date('3-mrt-2017 23:45:12','dd-mon-yyyy hh24:mi:ss') from dual


ERROR at line 1:

ORA-01843: not a valid month

SQL> select fnd_date.string_to_date('3-mrt-2017 23:45:12','dd-mon-yyyy hh24:mi:ss') from dual;



03-MAR-2017 11:45:12PM

SQL> select fnd_date.string_to_canonical('3-mrt-2017 23:45:12','dd-mon-yyyy hh24:mi:ss') from dual;



2017/03/03 23:45:12


HTH. As always, feel free to leave comments and questions.

New article on Descriptive Flexfields

I just published the second part of the article series on Flexfields. This part is about Descriptive Flexfields. It is available from:

The next part will follow shortly, and will discuss the flexfield datamodel.

New article on eBS (Key) Flexfields

Just a short note to point to a new article that I published on the new site:

It is the first part of a multi-part article. This part explains Key Flexfields in eBS. The next parts will discuss Descriptive Flexfields, the datamodel and special features. 

Update on PLSQL validation


At the flexfields presentation at UKOUG, I promised an update on the PLSQL validation.

It turns out, that the only problem was a missing ” at the end of the function. Here is the code for the function: 


FND PLSQL ” declare

v_value varchar2(10) := :!value ;

v_num number;



  if mod(v_num,2)!=0 then


  end if;


   when others then


     fnd_message.set_token(‘MESSAGE’,’This is not a valid number’);


end; “


So, use only the validate event:


And the parameter will validate correctly:

Good luck on your own experiments!


New website and article

It's been a while since I last posted an article here. 

A long vacation, and testing different CMS's for the website account for the lost time. So I decided to give Joomla a try. I just finished installing the components that I want to use. And I wrote a short article, to see how it goes.

I'll be transferring the articles from this website to the new one in the days to come. 

For now, take a look at the new website:

The article that I wrote is about adding a column to OA-Framework without using jDeveloper to change the VO. I describe how to use a descriptive flexfield to add a checkbox to the framework page.

You can read the article here: here.

Special and Pair validation types

I am working on an article about flexfields and flexfield validation.

Even though the article is not yet finished, I thought the part about ‘SPECIAL’ and ‘PAIR’ validation types might be interesting enough. Many people seem to think they can only use the seeded validation sets. However, you can also create your own validation sets. And their options are very powerful. So I wanted to publish this part of the article as a prelude to the full story.


Special Validation

Special validation is used to provide flexfield functionality for a single value. What that means is that you can have for example a concurrent program parameter that will be filled with a Key flexfield value, or a range of flexfield values.

Let’s go back to the Key Flexfield. We know that they are combinations of different segment values that are stored in a separate combination table.

When you want to submit a key-flexfield combination as a parameter to a concurrent program, you can code your own validation for the separate values. But you’ll be missing the nice functionality that gives you pop-ups, a validation over the resulting combination and if needed the ID-value for the flexfield combination.

That is possible with a ‘Special’ validation type.

The special validation uses a number of user exits to enter, validate and query keyflex segments. With special validation, you will be able to enter one or more segment values for a key flexfield. To enter these segment values, 3 user exits can be used. They are: ‘POPID’, ‘VALID’ and ‘LOADID’.

POPID is used to enable the user to enter the flexfield segment value. It is called when the users cursor enters the segment value field. With this user exit, you decide which segment values should be shown, and how they should be shown.

 VALID is called when the user exits the segment value, or confirms the chosen flexfield combination. It validates the entered value against the values existing in the key flexfield table.

LOADID is optional, and it can be used to choose which information will be returned as flexfield value. This can be the concatenated segments, or the id-value for the flexfield combination or segment values.

These 3 user exits can be assigned to 3 ‘events’. There are more events possible, but they are either not yet in use, or their use is not yet supported. So we will only use ‘Validate’, ‘Edit’ and ‘Load’.

Sounds complicated, so far? Don’t worry; this is not an easy validation. But we’ll build some examples to give you an idea. First we start with building a very easy special validation. This will be built on our Code Combination key flexfield. We’ll be using a concurrent program ‘Test Flex Validation’ program to see our different options.

This program is based on the following procedure:


( errbuf   out varchar2

, retcode  out varchar2

, p_flex   in  varchar2

, p_flex2  in  varchar2 := ‘XXX’

, p_flex3  in  varchar2 := ‘XXX’

, p_flex4  in  varchar2 := ‘XXX’

, p_flex5  in  varchar2 := ‘XXX’

) IS









This will only write the parameter value to the output of the request. To use flexfields as parameters for concurrent programs, we need to define a value set based on them.

We will start with the barest setup to enter a key-flexfield combination. For this article, we use the accounting flexfield, with code ‘GL#’  and id-num ‘101’.

In this case, we have the following definition:


So what does this mean?

The first box is for the edit event. This will be triggered when the user enters the cursor into the field with this value set.

FND POPID         This is the user exit to pop up a flexfield screen, and let the user enter the flexfield values.

CODE="GL#"     This is the flexfield code for the key flexfield that we will be using.

APPL_SHORT_NAME="SQLGL" The short name for the application the flexfield belongs too. Together with ‘Code’, this will identify the flexfield itself.

NUM="101"       The id-number for the flexfield structure. If you have only a single structure flexfield, it is optional. For flexfields enabled for multiple structures, you need to enter the id-number.

VALIDATE="PARTIAL"   Validate can be ‘None’, ‘Partial’ or ‘Full’. None means the combination is not validated. Partial means that the separate segments are validated, there is no validation if the combination exists. Full means that segments and combination will be checked, and if a new value is entered, this will be inserted into the key flexfield table.

SEG=":!VALUE"                This is the forms field that will be used to store the value of the segments.

The second box is for the ‘Validation’ event. This code will be called when the user navigates out of the field, or submits the entire combination.

Now when we set this value set as a parameter for our concurrent program, we can see how the validation works:


Now when we run the program, we get this pop-up:


We have all the functionality of the key flexfield. We can use the ‘Combinations’ button to search for existing combinations, and all separate segments will be validated, as will be the final combination.

When we submit a value to our program, it will show the concatenated segments as the value of our parameter:


Now let’s see some more features of this validation. For example, we’d like to have the value of the combination id. (CODE_COMBINATION_ID in our case, since we use the Accounting Flexfield).

To get that, we need to add the LOADID user exit:


The ‘Load’ event will get the combination-id from the flexfield table. This is only possible for the ‘VALIDATE=”FULL”, since it will validate the whole combination. Also we need to set the ID=”:!ID”. This will populate the :!ID column with the ID value of the combination.

Finally, I added the ‘DINSERT=”NO” ‘, because we don’t want to allow insertion of new code combinations from this value set. (And Validation=”FULL” by default inserts new combinations into the flexfield column).

Now when we run the concurrent request, we see that the parameter value is the code_combination_id instead of the concatenated segments:

With these user exits it is also possible to select just a number of segments, instead of the whole combination. For this we remove the ‘Load’ / ‘LOADID’ part again.

Then we add a ‘DISPLAY=”x” ‘ to the ‘Edit’ and ‘Validate’ user exits. The “display” parameter is defaulting to ‘ALL’. But you can also specify separate segments by their sequence number or names. In our case, we display the first 2 segments:


Now when we run the concurrent program, we get a pop-up for only the first 2 values:


A very nice feature (at least as far as I’m concerned) is the use of a where clause on the combination values. Consider the following ‘Enter’ code:






TITLE="Special Validation Key"




WHERE="segment2 not like '1%' "


The “WHERE” clause prevents us from choosing combinations that have a segment2 starting with ‘1’. When we run our concurrent program with this, and choose the combinations:



There is no Dpt starting with 1.


When we add the “WHERE”-clause to the validation event too, it will prevent us from entering the values manually:




The last feature that we’ll look into is the use of a pl/sql validation through the special validation routines. By using the user-exit PLSQL, we can call an anonymous PL/SQL block in our ‘Validation’ event. I created a value set with the following function for the ‘Validation’ event:


FND PLSQL " declare

  v_value varchar2( 10 ) := :!value ;

  v_sum number;

  v_valid boolean;



   for i in 1..length(v_value) loop

    v_sum :=v_sum+(length(v_value)+1-i)*substr(v_value,i,1);

  end loop;

  if mod(v_sum,11)=0 then

     v_valid := TRUE;



  end if;

  if not v_valid then

      fnd_message.set_name('FND','FND_GENERIC_MESSAGE' );

      fnd_message.set_token('MESSAGE','This is not a valid bank account');


  end if;

END; "



This PL/SQL procedure validates a (Dutch) bank account number. If it does need pass the test, a message will be displayed. This gives you almost unlimited possibilities for validating entered data.

As you can see, it is only a ‘Validate’ event. Because we don’t need any special functionality for entering the data. We can limit the entry to numbers only on the ‘Validation Set’ main page.


Now when we use this value set for our concurrent program, we can only enter valid dutch bank accounts:





The list of parameters for the user exits is longer than this. So we won’t be going through all the possibilities. You can check the Developers Guide and the Flexfield guide for a complete listing of options. (Did you notice the flexfield title that I sneaked into the pop-up? Try and find the option for that!)

Please try the different options for yourself, and realize the possibilities of the special validation.


Pair Validation

Meanwhile, we’ll continue to the ‘Pair’ validation. The pair validation is very much like the ‘special’ validation. It uses the same kind of user exits, but this time, a range of segment values or combinations is selected.

Let’s first create a range of the account segment. Instead of using POPID and VALID, we use POPIDR and VALIDR. The R-version of the user-exits automatically create a range.

Of course we need 2 parameters to set the range. However, we need only one validation set.

I created the validation set ‘XXX_PAIR_VAL’. I entered only the edit and validate events:


The next step is to set the parameters for both the low and high value. Both parameters have the validation set ‘XXX_PAIR_VAL’.


Now when we run the program, we can enter a range. This includes validation that the high value is indeed higher or equal to the low value.


Of course the concurrent program will receive the values for 2 parameters.


When we use the full validation we can enter a range of the whole account combination. Note that we cannot use the FULL validation for pair-validation. Because that would mean the use of the combination-id from the flexfield table and based on the combination-id’s you cannot build a range.


So we can only use PARTIAL and NONE for the validation. For that same reason, I have not yet had a reason to use a LOAD event for PAIR validation. It is however allowed to use one.


I created a PAIR validation for the whole accounting range as follows:



When used in the concurrent program, it will indeed allow us to enter a range of all segments:



That completes the chapter on PAIR validation too.


Oracle eBS 11i Infrastructure

Oracle eBS 11i Infrastructure


In this article we will describe the infrastructure of Oracle eBusiness Suite (eBS). In its simplest form, eBS is a 3-tier application with a client tier, Application-tier and DB-tier.


Let’s start with the DB-Tier. Surprisingly, the database tier has only very little eBS specific features.

Of course we need a database (instance) and therefore an ORACLE_HOME. But the database can either be a single-instance or a RAC-installation and all Oracle RDBMS features are transparently available for eBS.

The management of the RDBMS Installation is also independent of eBS.


DB-Tier filesystem

Let’s start with the filesystem on the DB-Tier. Of course there is an Oracle_home installation needed, for the RDBMS-Instance. This will be installed during installation of eBS. But also a fresh installed ORACLE_HOME can be used, with an eBS database.

In the ORACLE_HOME, an extra directory is added. The Appsutil directory. This directory contains the software and data needed for running Autoconfig and Rapidclone.

All other directories are at the discretion of the eBS DBA.

Oracle Instance

When we look at the instance to run eBS, we find a number of mandatory parameters for eBS. These are found in Metalink notes 216205.1 and 396009.1 (At the time of writing. Please verify these notes for yourself).

These parameters are recommended or mandatory based on testing by Oracle Corp. They will automatically be set by the eBS installer. But you should take note of them when you use a fresh installed ORACLE_HOME.

Then we finally come to the contents of the database.

The eBS Database

Let’s start with the schemas in the database. Oracle eBS creates a separate schema for every module. The schema is named as the short_name of the module, for example AP (Oracle Payables / Accounts Payable), AR (Oracle Receivables / Oracle Receivables).

There is a separate schema for the Application owner APPS.

The Application schemas contain the tables, indexes and sequences for the different applications. All objects in these schemas (except indexes, of course) have a synonym in the APPS Schema. In the APPS Schema we also find all PL/SQL objects, views and Materialized Views.

A major part of eBS is written in PL/SQL. All PL/SQL objects are also installed in the APPS Schema.

User sessions within eBS will usually run in the APPS Schema as well.

That brings us to an extra schema in the database: APPLSYSPUB. This schema has access to some of the eBS tables and packages, that allow it to validate eBS logins and start an APPS-session based on that login information. We will see the details of this later on.

Before release 11.5.2 every schema had its own tablespace. However, the number of modules for eBS (and with that the number of schemas) is ever increasing. So managing the database became more and more complex. In 11.5.2 Oracle introduced the Oracle Applications Tablespace Model (OATM). Within this model, the tablespaces in eBS are based on functionality, rather than schemas.

In this model, we see the following tablespaces:

APPS_TS_TX_DATA – Containing all transaction tables, Materialized Views and IOT’s

APPS_TS_TX_IDX – Containing all indexes for transaction tables

APPS_TS_SEED – Containing the tables and indexes with seeded data (as opposed to transaction data).

APPS_TS_INTERFACE – For Open Interface tables

APPS_TS_SUMMARY – Contains summary tables for several modules (AR, PA, BIM, etc)

APPS_TS_NOLOGGING – For tables and objects that are created with the NOLOGGING option

APPS_TS_ARCHIVE – Containing archive and history tables (and indexes)

APPS_TS_QUEUES – Containing the AQ (Advanced Queuing) objects

APPS_TS_MEDIA – Containing tables with LOB’s. For media objects or documents.

The Undo and Temp tablespaces are not part of the tablespace model.


Application Tier

Now it’s time to look at the Application Tier. In fact the Application Tier consists of 3 different services: Web service, Forms service and Concurrent Processing. In 11i installations, there is also an Administration service.

The Application Tier significantly changed from R11i to R12. We’ll discuss the 11i Apps Tier shortly, and then discuss the R12 tier in more detail.

The 11i infrastructure

Both the R11 and R12 infrastructure consist of a Web-service, a Forms Service and a Concurrent Processing part.

We will be discussing the different services here. The following picture shows all components and their communications. You might want to keep it for reference during this article.



R11i Web Service

For 11i, the web tier is built on Oracle iAS 9i. The iAS installation provides webservices (Apache HTTP/HTTPS), a Java Runtime Engine (JSERV) and a PL/SQL engine (modplsql).

The web service also acts a gateway for the Concurrent Request log and output files. And it is the first point of access when starting a forms session. (When using a socket forms connection, when using a forms servlet the web tier will host the forms process).

A detail from the picture above shows the iAS structure.


The core of iAS is the web server. This is the front-end for the client. Requests can also be forwarded to and from the forms server and the concurrent processing. We’ll see that in the next paragraphs.

Within the iAS Jserv and modplsql are plugins. They are the only components that communicate with the database. When they are called, they execute java (Jserv) or PL/SQL (modplsql) and return an html page. This page is then sent to the client through the HTTP service.

The Jserv delivers a Java Runtime Environment. In the Jserv, java servlets can be run. Also the JSP-files are executed in the Jserv. A JSP-file (Java Server Page) is a page with java code that returns an html-page (similar to the way scripting languages like PhP work). The java part is executed in Jserv, which returns the html to the webserver. The webserver redirects the html to the client.


Let’s take a closer look at the components and their executions:



The webserver is based on the regular Apache 2 webserver. The configuration file is also equal to the Apache config file. The configuration is set in httpd.conf (or httpds.conf for SSL).

Instead of starting the webserver through $APACHE_HOME/bin/httpdctl, we start through $APACHE_HOME/apachectl. The default port number used for eBS 11i is 8000. This is part of port-pool 0. For different port-pools, the port number is increased. So for port-pool 1 the webserver runs on port 8001.

The root directory for the webserver is set to $OA_HTML, which is by default $COMMON_TOP/html. This directory contains all *.html files for eBS.

A number of virtual directories are set up within eBS.



As mentioned before, java code is executed by Jserv. Jserv is a java servlet engine. That means that it can run both servlets and jsp-files.

These servlets are mostly located in the $JAVA_TOP. The *.jsp files are located in the $OA_HTML directory.

One of the options of Jserv is to create a database connection to the rdbms database. This is done by a JDBC Thin Client connection.

Before we look at the configuration for Jserv, examine the following picture.

Within Jserv, we can define different java environments, called zones. These zones are configured with different servlets or java archives (jar-files). Each zone is configured with its own configuration file. Within the zone the startup parameters (initargs) for the servlet are defined.

On the other side of the picture, you see a group. All java processes within Jserv are grouped together. You must define at least one group. The default group is ‘OACoreGroup’. Within each group, we create one or more processes that will be mapped to our zones.

This mapping is done by mounting the zones and the groups to different logical directories. In the picture, a mountpoint is created: /oa_servlets/. It refers to the group ‘OACoreGroup’, which holds 3 java processes. And it is mapped to zone ‘root’, which includes the servlet ‘dummy’ with a set of startup parameters.

When iAS receives a call to the virtual directory /oa_servlets/ it will be recognized as a Jserv mount point and the request will be forwarded to Jserv. In this example Jserv has 3 java processes in the group for this mount point. And they will be able to run all the servlets in the zone.

Sounds complicated? Take a look at the following configurations:


ApJServGroup OACoreGroup 3 1 /etc/oracle/iAS/Jserv/etc/

ApJServGroupMount /oa_servlets balance://OACoreGroup/root




root<host>.properties = /etc/oracle/iAS/Jserv/etc/

servlet.Dummy.initArgs=message=I'm a dummy servlet


Within jserv.conf we define a group called OACoreGroup. This group is running 3 Java processes. And the definition of the group is in the file. The 1 indicates the weight for load-balancing with multiple groups.

Then we mount the zone ‘root’ to the group ‘OACoreGroup’. This mount point is linked to the virtual directory /oa_servlets/.

The virtual directory is used for redirection to the JServ. When a request is made to the virtual directory Jserv will be called. The part of the URL after the virtual directory is the path to the servlet. This path will be searched for in the $CLASSPATH.

When the java servlets need to connect to the database, they can build a connection using JDBC. The access information is stored in a *.dbc file in $FND_TOP/secure. The dbc-file is referred to in the parameters for the zone.



Let’s take a look at the modplsql module. This module is designed to run pl/sql procedures within the database. The connection is based on the file. This file contains the DAD (Database Access Descriptor), including the access data to the eBS database.

The module is also called through a virtual directory. For example http://<host>:<port>/pls/TESTDB/ dummy. /pls/ is the virtual directory that refers to modplsql. TESTDB is the name of the DAD and dummy is the name of a pl/sql procedure accessible for the db-user from the DAD.


That concludes the 9i iAS module for now.



Let’s take a look at the forms server.

Oracle forms can be set up in two ways, socket connection and servlet. The default is socket connection. With a socket connection, a separate forms server and dedicated forms processes are used. For the servlet connection, a java servlet is called within the iAS.

The formsserver itself is installed in the 8.0.9 ORACLE_HOME. Forms has a forms server, and one or more client processes. The forms server is started with f60svr. It will spawn a f60webmx process for every client session connecting.

On the server side, forms are run in the forms client processes. On the client side, they are run in a java applet. When the client clicks a forms based function in the Personal Home Page, it calls an URL that refers to the forms client executable in the 8.0.6 ORACLE_HOME.

This URL is taken from the profile option ‘ICX: Forms Launcher’, and the default value is like ‘http://<server>:<port>/dev60cgi/f60cgi’. The parameters referring to the function being clicked are added to this URL as parameters. (i.e. the name of the form to be started)

When this URL is called, the webserver will execute the executable f60cgi. This executable returns a HTML page to the client. This page is called the ‘Base HTML’ for this forms server. (by default this is $OA_HTML/US/appsbase.htm)

This HTML page calls the J-initiator plugin (or the native JVM when configured). It also includes the parameters to connect to the forms server and the name of the form to start.

The J-initiator will start an applet on the client, which connects to the forms listener process. The forms listener process then assigns a dedicated forms client process.

At this point the whole chain looks like this:


The configuration for the forms server is in the appsweb.cfg file in ($OA_HTML/bin). This file contains the basic coloring scheme for the forms server, the forms settings and the referral information to the J-Initiator plugin. The plugin on the client side is called through its class-id, which is also set in the appsweb.cfg.


Concurrent Managers

The last part of the application tier is the concurrent processing part. The concurrent managers are used to execute background and batch processes.

Different executables including host-command files, pl/sql procedures, Oracle Reports, SQL*Loader control files and Binary executables can be defined to be run as concurrent programs. Parameters are also optionally defined with the concurrent programs.

The executable files are defined separate from the concurrent programs. So an executable can be run as different programs with different parameters.

The programs are executed through ‘Requests’. A request is started as a concurrent program and the values of its parameters. It can be scheduled to start at a specific time, or in a specific schedule. The output of the program can be sent to a printer. It is also available through the application.

This picture shows the relation between programs, requests and managers.


The managers

We’ll take a closer look at the concurrent programs later. Let’s first look at the concurrent managers. There are concurrent managers and transaction managers. Also a number of control managers are defined.

We’ll start with the ‘Internal Manager’. This is the first manager to be started. Its purpose is to control the stopping and (re-)starting of the other managers. When Generic Service Management is enabled (default as of 11.5.7), it delegates to the ‘Service Managers’. On every node where concurrent processing is enabled, a ‘Service Manager’ is started. However, only one Internal Manager is running at any time.

The other concurrent managers are defined with a work shift that controls how many processes a concurrent manager should have at certain times. The work shifts consist of a time-range and a number of processes. The Service Managers (or Internal Manager) will start and stop processes according to these work shifts.

Another part of the setup of concurrent managers is their specialization rules. The specialization rules indicate which programs are valid for a concurrent manager, or are excluded for that manager. They work on an include/exclude principle. When programs are included for that manager, the manager can only run those programs. When programs are excluded, the manager can run any program except the excluded ones.

When a request (to run a program) is submitted from eBS, it will be placed in FND_CONCURRENT_REQUESTS with a status_code ‘I’ (The eBS forms have fewer statuses than the codes in the table). The manager processes will query this table for requests that they are eligible to run.

Once a manager process finds a request with status_code ‘I’, which it is eligible to run then it will put the request on its own queue. It will then run the executable with the defined parameters. The logfile and outputfile are written to the filesystem in $APPLCSF/$APPLLOG resp. $APPLCSF/$APPLOUT.

There are some special cases that need to be discussed. The first is the incompatibility. Concurrent Programs can be made incompatible with each other. That means that they cannot run at the same time. Once a program is started that is defined as incompatible with another, it will be automatically put on the queue for the ‘Conflict Resolution Manager’. This special manager will check if any incompatible program is running or ‘Pending’ with code ‘I’. If so, it will hold the request on its own queue. If no incompatible program is running or ‘Pending’, then it will set the status of the request to ‘Pending’.

Another special case are the ‘Transaction Managers’. They are started and stopped the same way as the other concurrent managers. But they do not use the request queue. Transaction managers are called online from the eBS forms. And they execute a limited number of programs. These programs defined within their executables. They are called through the ‘FND_TRANSACTION.SYNCHRONOUS’ procedure, which uses the ‘DBMS_PIPE’ package.


The programs

It’s time to look at the concurrent programs. As mentioned before, a concurrent program is an instantiation of an executable. The executable is defined with a short name, an application (module), a filename and a method.

The short name will uniquely identify the executable. The other data is needed to determine what should be run for this executable. If the executable is an OS-based program, the application will be used to derive the directory on the file system where the executable is found.

When the executable is defined as PL/SQL, the filename will contain the procedure that needs to be run.

The concurrent program is defined as the executable with an (optional) set of parameters. It also has some properties for the printing of the output (print-style, pre-defined printer, size of the output).

Depending on the type of executable that needs to be run, the parameters will be sent to the executable ordered or named. For PL/SQL and host files, the parameters are ordered. And the order in which they are defined in the form defines how they will be sent to the executable. For reports the parameters are named, which means they are sent as <parameter>=<value>, ….

After the request has finished, the request table ‘FND_CONCURRENT_REQUESTS’ will be updated with the status information and a reference to the log- and output file. During the execution of the request, a status_code and phase_code are updated. The exact values of these fields are described in one of the next articles. That will go deeper into concurrent processing.

The output

The log- and output file from the requests are written to the directories $APPLCSF/$APPLLOG and $APPLCSF/$APPLOUT. But they of course also need to be made available to the user. This is done through the ‘Applications Report Review Agent’.

There is quite a lot of setup that can be done for the whole process. But within the scope of this article, we’ll only look at the basic architecture.

From the eBS form the log and output file are available from 2 buttons. These buttons call the web server for ‘FNDWRR.exe’ (.exe on both Windows and Unix).

FNDWRR.exe is a cgi-executable that will call the ‘FNDFS listener’.

This is an 8.0.6 TNS-listener in the eBS ORACLE_HOME on the eBS application tier. One of the less known features of the TNS-listeners is that they can do more than create database connections.

In the listener.ora, you can define a program to be called when a connection is made on a certain tns-entry. That feature is used for the FNDFS listener. When it is called, it will redirect traffic to the ‘FNDFS’ (FND File System) executable. This executable will read the requested file from the file-system and send it to FNDWRR.exe.

Again, we have a schema to show the whole flow:


This complex retrieval is of course needed because the concurrent processing tier can be separate from the forms and web-tiers.


eBS Troubleshooting

Oracle eBS troubleshooting


On this webpage, I’ll make a FAQ on common eBS problems and troubleshooting. Probably the format will change over time. But I’ll just start. I use basic flow diagrams, to give an overview of the process. Under the diagrams is an explanation of all the steps.

Ø My concurrent manager does not start


1)      Check if the Internal Manager is running. On Unix, you can run: ps –ef | grep ‘FNDLIBR FND CPMGR’. If this returns a process, check the start time for the process to make sure it is the correct process.

2)      If a process is returned, and it started at the time you started the managers, the ICM is running.

3)      The ICM is not running. First check the adcmctl.txt file. It is found in the process_log directory. (Check your autoconfig xml file or the script). It will show the logs for the start-up scripts of the ICM.

4)      The ICM is running, but can’t start the other managers. Most common cause is  the APPS Listener is down. Check for it running with: ps –ef  | grep ‘tnslsnr APPS_<SID>’

5)      If no process is returned, start the apps listener with Wait a minute afterwards, for the ICM to retry starting the managers.

6)      The ICM is running, or was started successfully before it died. Check the logfile from the ICM in $APPLCSF/$APPLLOG. By default the file is named <SID>_<proc>.mgr, where proc is the process_id from adcmctl.txt.


Ø Notifications are not being sent by the notification mailer


1)      Look for the notification in ‘wf_notifications’. Check the status, mail_status, recipient_role and notification_id.

2)      If Mail_status = ‘SENT’, the message has been mailed already. If status<>’OPEN’ (Note the difference between status and mail_status), the notification is not eligible to be mailed anymore.

3)      The Notification Mailer has already sent this message. Maybe it was sent to the TEST_ADDRESS  from the Notification Mailer.

4)      Check the mail_preference for the recipient_role from wf_roles.

5)      If the preference is ‘QUERY’, ‘SUMHTML’, ‘SUMMARY’ or ‘DISABLED’ then the recipient will not receive notifications by mail.

6)      Change the preference in the Users preferences. Or test with a different user.

7)  The Notification Mailer reads notifications to send from the queue WF_NOTIFICATION_OUT. Select from the queue-view:

select notification_id,msg_state,msg_id,role,corrid,enq_time,deq_time

from  (select msg_id, o.enq_time, o.deq_time, msg_state

              ,(select str_value

                from   table (

                where  name = 'NOTIFICATION_ID') notification_id

              , (select str_value

                 from   table (

                 where  name = 'ROLE') role

              , (select str_value

                 from   table (

                 where  name = 'Q_CORRELATION_ID') corrid

       from$wf_notification_out o)         

where notification_id=<notification_id>

and rownum=1;

8)      If you received a result on the query, the notification is in the queue.

9)      The status of the notification in the queue should be ‘READY’. If it is ‘PROCESSED’, or ‘ERROR’, the notification is already dequeued or errored. Otherwise check the status of the queue with:

select name,enqueue_enabled,dequeue_enabled

from dba_queues


10)   The status of the message should be ‘READY’. The ‘ENQUEUE_ENABLED’ and ‘DEQUEUE_ENABLED’ columns should be ‘YES’.

11)   Reprocess the message with the conc. Request. Or stop/start the queue with dbms_aqadm.

12)   Check the Notification Mailer logfile. The notification is ready for the mailer, but it is unable to pick it up. Check if the mailer shut down due to too many errors.

13)   The message is not in ‘WF_NOTIFICATION_OUT’. It can still be queued on the ‘WF_DEFERRED’ queue. Check this queue with:

select v.msg_id,v.msg_state,v.enq_time,v.deq_time,v.corr_id

from$wf_deferred v

,      table(v.user_data.parameter_list) t

where v.corr_id like ''


and value = <Notification_id>;

14)   If the query returned results and the msg_state is ‘READY’, the notification is still being processed. Skip to 16

15)   Unfortunately, your notification seems to have gone missing. Consult Oracle Support. Please inform us of the solution in this case, so we can extend the FAQ.

16)   The notification is still in the deferred queue, waiting to be picked up by the ‘Workflow Deferred Notification Agent Listener’. Check the status of this listener. And if needed, check its logfile.

17)   If the Deferred Notification Agent Listener is not running, or erroring

18)   (re)start it.

19)   Check if the Business Event ‘’ is enabled and has a subscription to procedure ‘Wf_Notification_Util.Denormalize_RF’.

20)   If either the Business event is disabled, or the subscription non-existent or disabled, go to 21.

21)   Make sure that the Business event is enabled and the subscription is valid and enabled. You will still have to reprocess the notification with the concurrent program to resubmit notifications.

22)   Unfortunately, we can’t locate the issue yet. If you manage to solve the issue please inform us, so we can update this FAQ.


Writing efficient SQL

The other day I gave a presentation on ‘Efficient SQL’. It was the first of a number of presentations, so I started with explaining some basic concepts.

Maybe it will be interesting for other people too. So here is the summary of it.




The main rules of efficient SQL are:

·         Less is better

·         More is better

That seems easy, since everything is better. But let me explain.

Less is better: The less I/O generated the better your statement will perform. Even though somebody might be able to think of some exceptions. It is safe to keep this as a rule of thumb.

Avoid unnecessary work for your query. You can do that by selecting only the rows that you need. (That sounds obvious, but I’ll give an example soon). In complex queries, make sure that you select the smallest possible set in every part of your query. Rather than collecting a huge amount of data and then selecting what you need, select the smallest set possible before you join.

Also select only the columns that you need. One argument is that it might give Oracle a chance to skip the table access, and use an index-only access.

Think about the use of ‘select *’. Most often this is a complete waste of resources. In packaged software, it can easily lead to bugs when the table definition changes. In all situations, it will cost extra resources to collect the data, send them to the client and then filter out the data that is not needed.


More is better: This is of course not about I/O. It is about the information that you give Oracle about your data and your query. Add as many predicates as possible, since it can help the optimizer do a better job. When 2 tables are joined on an ID-column. But you know, from your knowledge of the data, that another column can also be used as a join-condition then use both join conditions.

It will help the optimizer work out the relationship between the tables, and select the optimal plan. If 2 columns have related data, and the predicate on one column means that the other column is restricted too, put a predicate on both columns.


Consider the following:

SQL> create table Xxx_inner

  2  as select * from dba_objects

  3  where object_type='TABLE';


Table created.


SQL> create index xxx_inner_n1 on xxx_inner(object_id,object_type);


Index created.


SQL> create index xxx_inner_n2 on xxx_inner(Object_type);


Index created.


SQL> create table xxx_outer

  2  as select * from dba_objects;


Table created.


SQL> insert into  xxx_outer

  2  select * from dba_objects;


71136 rows created.


SQL> create index xxx_outer_n1 on xxx_outer(Object_id,object_type);


Index created.


SQL> create index xxx_outer_n2 on xxx_outer(object_type);


Index created.


SQL> analyze table xxx_inner compute statistics;


Table analyzed.


SQL> analyze table xxx_outer compute statistics;


Table analyzed.


SQL> set autotrace traceonly;

SQL> select o.*

  2  from xxx_outer o

  3  where o.object_id in (select object_id from xxx_inner i)

  4  and o.object_type='PROCEDURE';


no rows selected




        113  consistent gets

       1064  bytes sent via SQL*Net to client


Consistent gets is the number of times data was read from the buffer cache into our session memory. It is therefore a good measure of the amount of work a session needed to do while executing a query.

SQL> select o.*

  2  from xxx_outer o

  3  where o.object_id in (select object_id

    from xxx_inner i

    where i.object_type=o.object_type)

  4  and o.object_type='PROCEDURE';


no rows selected




         15  consistent gets

       1064  bytes sent via SQL*Net to client


SQL> select o.object_id

  2  from xxx_outer o

  3  where o.object_id in (select object_id

    from xxx_inner i

    where i.object_type=o.object_type)

  4  and o.object_type='PROCEDURE';


no rows selected




         15  consistent gets

        254  bytes sent via SQL*Net to client



Here we see two tables created from ‘DBA_OBJECTS’. We join these tables on ‘OBJECT_ID’. In this case, we have some information that the Oracle Optimizer does not have. The object_id,object_type combination is the same in both tables. Unaware of this fact, Oracle has to search all object_id’s for ‘XXX_INNER’. When we tell Oracle that the object_type is the same, it can skip most of the records resulting in less I/O.

When we finally tell Oracle that we’re only interested in the object_id, we also reduce the network traffic by 75%.


The concepts


For every query, Oracle will have to collect some data. And in most cases, it will have to join one or more data-sets. Let’s see what options Oracle has for collecting data and joining the data together. In this presentation we only look at the basic options, not the more sophisticated features. So don’t expect this list to be complete. We will see how data can be retrieved from the database, and how tables / data-sets can be joined together. We will not yet go into the most efficient way to do it, because the most efficient way to retrieve data depends on many factors. Only when you have a basic understanding of the concepts, we can start thinking about the most efficient way to do things.


Collecting data


To gather data from a table, Oracle can use 3 different options, called ‘Access Paths’:

·         Full Table Scan

·         Index Scan / Table Access by Rowid

·         Index Scan

The Full Table Scan (FTS) is exactly as the name implies, a full scan of the table. All the records of the table are read into memory, and checked against the predicates in the query (where clause or Join condition). The blocks of the table don’t have to be read in any particular order. Oracle will just try to get the blocks of the table as quickly as possible.

When a sizable part of the table needs to be selected, this will be the most efficient access path. It will be the only one available, if there is no predicate available that matches (part of) an index.

The ‘Index Scan / Table Access by Rowid’, will use an index to decide which rows need to be read into memory. Then based on the rowid in the index, the correct row will be retrieved. The rowid refers directly to the position on disk where the row is located.

And the last option is the ‘Index Scan’. The difference with the previous option is that Oracle does not need to get the table data anymore. The data in the index is sufficient to answer the query.


So which one of these is the most efficient?

As usual, it depends. Many people think a FTS is less efficient than an Index Scan. But consider this:

SQL> create table xxx_access as select * from dba_objects;


Table created.


SQL> create index xxx_access_n1 on xxx_access (object_id);


Index created.


SQL> select object_id,object_name from xxx_access where object_id>0;


71139 rows selected.


Elapsed: 00:00:08.02


Execution Plan


   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=287 Card=78799 Bytes=6225121)

   1    0   TABLE ACCESS (FULL) OF 'XXX_ACCESS' (TABLE) (Cost=287 Card=78799 Bytes=6225121)




       5803  consistent gets

    2727442  bytes sent via SQL*Net to client

      71139  rows processed


SQL> select /*+ INDEX (xxx_access) */ object_id, object_name from xxx_access where object_id>0;


71139 rows selected.


Elapsed: 00:00:10.05


Execution Plan


0     SELECT STATEMENT Optimizer=ALL_ROWS (Cost=1290 Card=78799 Bytes=6225121)

1   0   TABLE ACCESS (BY INDEX ROWID) OF 'XXX_ACCESS' (TABLE) (Cost=1290 Card=78799 By=6225121)

2   1     INDEX (RANGE SCAN) OF 'XXX_ACCESS_N1' (INDEX) (Cost=161 Card=78799)




      10771  consistent gets

    2727442  bytes sent via SQL*Net to client

      71139  rows processed


The FTS needs 5803 I/O operations. While the Index Scan takes almost double at 10771 I/O’s and 2 seconds more. (out of 10 sec’s!)

Imagine what will happen, when you try this with a multi-million row table.


But for sure an Index Scan will be the most efficient when it can be done? Again, it depends. Consider this:


SQL> create table test1 (l number, txt varchar2(500));

Table created.


SQL> create index test1_idx on test1(l,txt);

Index created.


SQL> Begin

  2  For I In (Select  Level L, Rpad('ABC',500,To_char(Level)) Txt

  3            From Dual Connect By Level <= 50000) Loop

  4    Insert Into Test1 Values (I.L,I.Txt);

  5    If Mod(I.L,5)!=0 Then

  6       Delete From Test1 Where L=I.L;

  7    End If;

  8  End Loop;

  9  Commit;

 10  end;

 11  /

PL/SQL procedure successfully completed.


SQL> analyze table test1 compute statistics;

Table analyzed.


SQL> set autotrace traceonly;

SQL> select l from test1 t where l>0;

10000 rows selected.


Execution Plan


   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=773 Card=10000 Bytes=40000)

   1    0   TABLE ACCESS (FULL) OF 'TEST1' (TABLE) (Cost=773 Card=10000 Bytes=40000)




       1393  consistent gets

     140549  bytes sent via SQL*Net to client

      10000  rows processed


SQL> select /*+ INDEX(t,test1_idx) */ l from test1 t where l>0;

10000 rows selected.


Execution Plan


   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=3338 Card=10000 Bytes=40000)

   1    0   INDEX (RANGE SCAN) OF 'TEST1_IDX' (INDEX) (Cost=3338 Card=10000 Bytes=40000)



       4003  consistent gets

     140549  bytes sent via SQL*Net to client

      10000  rows processed





How can the Full Table Scan be more efficient?


Good question. To answer it, we have to look at the amount of work that Oracle has to do to get the data. We start with the FTS:

As mentioned, a FTS needs to scan all the blocks in a table. In my system, the table XXX_ACCESS was created with 1152 blocks. So basically Oracle will read 1152 blocks. However Oracle has optimized this process. One of the most noticeable optimizations is the db_file_multiblock_readcount, which tells Oracle to read multiple blocks in one I/O operation. So instead of doing 1152 reads, Oracle reads 4 (on my system) blocks at a time in 288 reads. (Take a look at the explain plan above again, and notice the cost of the Full Table Scan!).

Now how much work does an Index Scan / Table Access rowid need to do?

To answer that question, you need to know the structure of an index. An index in Oracle is a B-Tree structure. It looks like an inverted tree, with the top being the ‘Root-block’. The lowest level contains the ‘Leaf blocks’, that hold the index keys and the matching rowid’s. The index keys in the leaf blocks are sorted. So the lowest value will be in the utter-left block, the highest in the far right block.

All upper level blocks show the ranges that the lower level blocks contain.

To find a range of data, Oracle starts at the root block, and follows the pointers to the first leaf block containing an index key within the range. From here Oracle can walk the leaf blocks from left to right (or right to left, if needed).

See the following picture:

That means that Oracle has to walk the ‘height’ of the index (Index level). Then read a number of leaf blocks. And for every entry in the leaf-block, it needs to retrieve the data from the table.

In the worst case scenario, the data is spread throughout the table. And for every index key, Oracle has to retrieve a different table block. In that case, the amount of work is: (index level – 1) + number of index leaf blocks + (Number of keys * Number of table blocks).

It will be obvious that is a lot more I/O than just reading the table once. The formula is not completely correct, because Oracle does not read the same table block twice, when the next rowid from the index is in the same block.

But the formula should make it clear that with more data being retrieved, the cost of the index access / Table Rowid, is increasing faster than the cost of the Full Table Scan.


What happened to Index Only Access?


The example showed that a Full Table Scan is still more efficient than using only an index. Even though Oracle would only have to walk through the index to retrieve all the data.

This is caused by a feature of the index structure and the way the data was entered into the table. This caused the index to grow bigger than the actual table:

SQL> select table_name,num_rows,blocks from dba_Tables where table_name='TEST1';



——————– ———- ———-

TEST1                     10000        772


SQL> select index_name, distinct_keys, leaf_blocks from dba_indexes where index_name='TEST1_IDX';



——————– ————- ———–

TEST1_IDX                    10000        3334


This situation can occur when a lot of inserts and deletes are taking place in the same transaction. The space for the deleted table rows can be reused immediately. But the space for the deleted index keys only comes available after the commit. NOTE: The space in the index will be reusable after the commit!

Another situation where this can happen is with an index key based on a sequence. So new data is only inserted at the end of the range. When you delete a lot of values on the lower end of the range (but not all). Richard Foote has some excellent material on his website about Deleted Index Keys:


Join Mechanisms


I hope you’re not yet in despair. Because so far we have only retrieved data from single tables. In most cases, we need to join tables together to get our data. Now we will look at 3 basic forms of joining data-sets together. Note that it is not necessarily only tables that we join. It can also be a result set from an earlier part of your query. For example we might collect some data from an Index Only Access and then join it to data from a Full Table Scan.

Oracle has 3 mechanisms to perform Joins: Nested Loops, Hash Join, Merge Join. Let’s take a look at them.

Nested Loops


The Nested Loop join loops over a smaller data set, and for every record in that set, it searches a matching record in the second data set. Visually, it looks like this:


You can see that the first set is fully scanned. This is the Outer or Driving Set. For every record in this set, we look up a matching record in the second set. Usually this will be done through an index, even though this is not mandatory.

The efficiency of this mechanism depends on the size of Set A, and the number of records we need to  retrieve from Set B.

We will see some situations where a Nested Loops join is more or less efficient.

The second join mechanism is the

Hash Join


For a Hash Join, Oracle builds a hash table from a (preferably) smaller data set (Build set), where the key is a hash value derived from the join columns. Then Oracle reads the second data set (Probe set), derives the hash value on the join columns and probes the hash table for a match.

Schematically, it looks like this:

For the Hash Join, it is not relevant if the data is retrieved through an index, or from a Table scan. Both data sets need to be read fully. One of the features of hashing is that collisions may occur. A collision means that 2 different values result in the same hash value. Therefore, the full data set is stored in the hash table. When a match is found on the hash values, Oracle double-checks the actual values of the join columns to see if they match.

There is a major drawback for this mechanism. When the hash table does not fit into the available memory (hash_area_size). Then Oracle will dump parts of the hash table to disk (Temp tablespace). A bitmap of all possible hash values is kept in memory with a bit indicating if a hash-value is used or not.

So while scanning the Probe set, Oracle can check if there is a possible match. If that part of the hash table is not in memory, Oracle will set aside the records from the probe table. When finished with the probe set, the next part of the hash table is loaded into memory, and the records that were set aside are tested again. This is called a ‘Multipass Hash Join’, instead of the ‘Onepass Hash Join’ where the entire hash table is held in memory.

You can imagine that the hash join can be very efficient even without index access. However it can deteriorate quickly when a ‘Multipass Hash Join’  is needed.

That brings us to the

Merge Join


A Merge Join is possible when 2 datasets are both ordered on their join columns. The datasets can then be read in an alternating way. You start reading the first dataset, then you read the second dataset until you find a matching value, or exceed the value. If it is a matching value, you can start building your result set. If you pass the join value, you continue reading the first dataset again.

Schematically, it looks like this:

 The main requirement is of course that both data sets are ordered, before the join takes place. If that is the case, this is probably the most efficient join mechanism. It can handle all kinds of join comparisons, including range comparisons.

Back to efficient SQL


Now it is time to go back to the main focus of this article. How to write efficient SQL.

We have seen how Oracle can access data and join it together. It is the job of the Oracle Optimizer to find out the most efficient way to do that, for a given query. It does this based on statistics on the tables and indexes. It is not in the scope of this article to discuss how to gather statistics. But we will see the use of several of the statistics. These statistics include (but are not limited to) the number of rows in the table, the number of blocks, the average row length, etc. For an index, they include (but are not limited to) the number of leaf blocks, the number of keys per leaf block, the number of datablocks in the table per key, etc.

In an ideal world, we would be able to trust the optimizer to do the right thing all the time.

However, we live in an imperfect world, and the Oracle Optimizer does not always have perfect information about the data or your query. Either the statistics might not be up to date, or they might not include some dependencies within the data. Also your query might not give the optimizer all the information that you have. (see the first example in this article, where we can give the optimizer extra information by adding a predicate).

Consider this query:

Select * From

Tiny  T, –7089 rec

Small S   — 71151 Rec

Where t.Object_id = s.Object_id;


Which explain plan is more efficient:



1  HASH JOIN        






0 SELECT STATEMENT                      


2   NESTED LOOPS                       

3    TABLE ACCESS FULL         TINY    



The first explain plan uses a Hash Join, with Tiny as the Build Table. The second uses a Nested Loops Join, with Tiny as the Inner Table.

I hope you have decided that you don’t know which one is the most efficient. Because you cannot know based on the information you have. If I selected 2 non-overlapping sets of data, the Nested Loop Join might be more efficient.  It would scan Tiny for 7089 records, then do 7089 index lookups on Small (without result), so it would need to read approximately 7089+7089=14178 blocks.


If the 2 sets would have a 1-n relationship, and every occurrence of object_id in Small is also in Tiny, both tables would need to be read fully and the Hash Join would be more efficient.


That means that to write efficient SQL, you’ll need to have an understanding of the data. And you must have considered the optimal execution plan for your query. When you write your query, keep in mind the mantra in first part of this article. Less is Better, More is Better. You want to give Oracle as much information as possible, and you want to get as small as possible result sets.


The last part that we will do in this part, is to look at the

Explain plan


To see what Oracle will do when executing a query, you can make an explain plan. Many tools have built-in options to show explain plans on queries. Alternatively, you can use the Oracle commands:

SQL> Explain plan for

  2  Select * From

  3  Tiny  T, –7089 rec

  4  Small S   — 71151 Rec

  5  Where t.Object_id = s.Object_id;




SQL> select * from table( dbms_xplan.display() );




Plan hash value: 803478362



| Id  | Operation          | Name  | Rows  | Bytes | Cost (%CPU)| Time     |


|   0 | SELECT STATEMENT   |       |  7089 |  1287K|  1264   (1)| 00:00:16 |

|*  1 |  HASH JOIN         |       |  7089 |  1287K|  1264   (1)| 00:00:16 |

|   2 |   TABLE ACCESS FULL| TINY  |  7089 |   650K|   213   (0)| 00:00:03 |

|   3 |   TABLE ACCESS FULL| SMALL | 71151 |  6392K|  1049   (1)| 00:00:13 |






Predicate Information (identified by operation id):



   1 – access("T"."OBJECT_ID"="S"."OBJECT_ID")


15 rows selected.


I took the previous query, and ran an explain plan on it. First I should tell you how I created tiny and small, so you can verify:


create table tiny as select * from dba_objects where mod(object_id,10)=0;


create table small as select * from dba_objects;


create index tiny_idx on tiny(object_id);


create index small_idx on small(object_id);


Analyze Table Tiny Compute Statistics;


analyze table small compute statistics;


You can see that both tables were created from dba_objects and tiny is a subset of small. Therefore a Hash Join makes most sense.


Let’s take a closer look at the explain plan now. Keep in mind that all the numbers are estimates from the optimizer. They are based on the statistics available, and the runtime numbers might be completely different.

The execution starts at the rows furthest right. And top down. In this case that means that we start with a Full Table Scan of Tiny. Then we do a Full Table Scan of Small, and finally we Hash join the 2 sets together.

The result of the Hash Join is returned, and becomes the result of the query (Select).


Let’s take a closer look at the Full Table Scans. After the name of the table, we see ‘Rows’,’Bytes’,’Cost’ and ‘Time’.

The ‘Time’ is an estimate of the amount of time it will take to complete this step. It is useful in query tuning  to see which step will take the most time.

The ‘Bytes’ are an estimate of the amount of data used to complete this step. I find it useful when a hash join is involved. Because when it exceeds my hash_area_size, Oracle will need a ‘Multi-Pass Hash Join’.

The ‘Cost’ is often used for query tuning, and people will try to ‘tune down’ the cost. This makes sense, because the cost is an estimate for the amount of I/O Oracle needs to do for this step. However, there is a logical trap in this.

Oracle has used the cost of different explain plans for the original query to decide the most efficient one. Now when we change the query, the cost can no longer be compared to the original query. After all, it is a different query. It will return a different result. Unless, of course there is some information about the data we are selecting, that we didn’t give the optimizer initially.


To me, it makes more sense to look at the ‘Rows’. This is the number of records Oracle expects from that step in the query. If this is very different from the number you are expecting, something is wrong. Either the statistics are outdated, or the Optimizer is missing some information that you have, or you are not selecting the data you are expecting.


In the query above, we see that Oracle has made the perfect assumptions. Tiny will return 7089 rows, Small will return 71151 rows and there is a 1-1 relationship  between them. So the join will return one record for each record in Tiny. No use looking for a more efficient plan here. Unless again, we did not query what we are looking for.