July 15, 2025
How to configure Oracle Listener Step-by-Step Guide
Oracle Listener
- A server-side
process that listens for incoming client connection requests to Oracle
databases.
- Uses
the listener.ora configuration file, typically located in:
- $ORACLE_HOME/network/admin
(Linux)
- %ORACLE_HOME%\network\admin
(Windows)
Step-by-step Listener Configuration
Create/Modify listener.ora
Configure tnsnames.ora
Start the listener (lsnrctl start)
Test connectivity using tnsping
Register services if needed (ALTER SYSTEM REGISTER)
Step1:Check if a listener is already running
lsnrctl status
- If it
says TNS-12541: TNS:no listener, no listener is running.
- Otherwise, it will display current listener status.
Step2️: Create/Modify listener.ora
cd $ORACLE_HOME/network/admin
Open listener.ora in your editor:
vi listener.ora
Add or modify:
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS =
(PROTOCOL = TCP)(HOST = your-hostname-or-ip)(PORT = 1521))
(ADDRESS =
(PROTOCOL = IPC)(KEY = EXTPROC1521))
)
)
Explanation:
- PROTOCOL
= TCP: Network protocol.
- HOST:
Your server hostname or IP (localhost if local).
- PORT =
1521: Default Oracle listener port.
- PROTOCOL
= IPC: For local (inter-process) connections, including external
procedures.
Step3️:Create/Modify tnsnames.ora
(Client/Server)
In the same folder, edit tnsnames.ora:
ORCL =
(DESCRIPTION =
(ADDRESS =
(PROTOCOL = TCP)(HOST = your-hostname-or-ip)(PORT = 1521))
(CONNECT_DATA =
(SERVER =
DEDICATED)
(SERVICE_NAME =
orcl)
)
)
- ORCL is
your connection alias.
- SERVICE_NAME
should match your database service name (select value from v$parameter
where name='service_names';).
Step4️: Start the Listener
lsnrctl start
Verify:
lsnrctl status
You should see your listener, hostname, and port.
Step5: Test Listener Connection
tnsping ORCL
Expected output:
scss ok (20 msec)
This confirms your listener is reachable.
Step6: Add Database to Listener (if not automatically registered)
In SQL*Plus as SYSDBA:
ALTER SYSTEM REGISTER;
This will dynamically register your database with the
listener (Dynamic Service Registration).
Verify using:
lsnrctl services
You should see your database service listed under the
listener.
Step7: Stopping the Listener
To stop:
lsnrctl stop
To restart:
lsnrctl reload
Troubleshooting Tips
✅ Ensure port 1521 is open in
your firewall.
✅
Check listener.log in $ORACLE_HOME/network/log.
✅
If TNS: no listener, ensure the listener is running.
✅
Ensure your SERVICE_NAME in tnsnames.ora matches the database service name.
✅
Use ALTER SYSTEM REGISTER if the service does not appear after starting.
June 05, 2025
Software Development Life Cycle
Software Development Life Cycle
(SDLC) is a process used by the software industry to design, develop and test
high quality softwares. The SDLC aims to produce a high-quality software that
meets or exceeds customer expectations, reaches completion within times and
cost estimates.
- SDLC is the acronym of Software Development Life Cycle.
- It is also called as Software Development Process.
- SDLC is a framework defining tasks performed at each
step in the software development process.
- ISO/IEC 12207 is an international standard for software
life-cycle processes. It aims to be the standard that defines all the
tasks required for developing and maintaining software.
What
is SDLC?
SDLC is a process followed for a
software project, within a software organization. It consists of a detailed
plan describing how to develop, maintain, replace and alter or enhance specific
software. The life cycle defines a methodology for improving the quality of
software and the overall development process.
The following figure is a graphical
representation of the various stages of a typical SDLC.
A typical Software Development Life
Cycle consists of the following stages −
Stage 1: Planning and Requirement Analysis
Requirement analysis is the most important and fundamental stage in SDLC. It is performed by the senior members of the team with inputs from the customer, the sales department, market surveys and domain experts in the industry. This information is then used to plan the basic project approach and to conduct product feasibility study in the economical, operational and technical areas.
Planning for the quality assurance
requirements and identification of the risks associated with the project is
also done in the planning stage. The outcome of the technical feasibility study
is to define the various technical approaches that can be followed to implement
the project successfully with minimum risks.
Stage
2: Defining Requirements
Once the requirement analysis is
done the next step is to clearly define and document the product requirements
and get them approved from the customer or the market analysts. This is done
through an SRS (Software Requirement Specification) document which
consists of all the product requirements to be designed and developed during
the project life cycle.
Stage
3: Designing the Product Architecture
SRS is the reference for product
architects to come out with the best architecture for the product to be
developed. Based on the requirements specified in SRS, usually more than one
design approach for the product architecture is proposed and documented in a
DDS - Design Document Specification.
This DDS is reviewed by all the
important stakeholders and based on various parameters as risk assessment,
product robustness, design modularity, budget and time constraints, the best
design approach is selected for the product.
A design approach clearly defines
all the architectural modules of the product along with its communication and
data flow representation with the external and third party modules (if any).
The internal design of all the modules of the proposed architecture should be
clearly defined with the minutest of the details in DDS.
Stage
4: Building or Developing the Product
In this stage of SDLC the actual
development starts and the product is built. The programming code is generated
as per DDS during this stage. If the design is performed in a detailed and
organized manner, code generation can be accomplished without much hassle.
Developers must follow the coding
guidelines defined by their organization and programming tools like compilers,
interpreters, debuggers, etc. are used to generate the code. Different high
level programming languages such as C, C++, Pascal, Java and PHP are used for
coding. The programming language is chosen with respect to the type of software
being developed.
Stage
5: Testing the Product
This stage is usually a subset of
all the stages as in the modern SDLC models, the testing activities are mostly
involved in all the stages of SDLC. However, this stage refers to the testing
only stage of the product where product defects are reported, tracked, fixed
and retested, until the product reaches the quality standards defined in the
SRS.
Stage
6: Deployment in the Market and Maintenance
Once the product is tested and ready
to be deployed it is released formally in the appropriate market. Sometimes
product deployment happens in stages as per the business strategy of that
organization. The product may first be released in a limited segment and tested
in the real business environment (UAT- User acceptance testing).
Then based on the feedback, the
product may be released as it is or with suggested enhancements in the
targeting market segment. After the product is released in the market, its
maintenance is done for the existing customer base.
SDLC
Models
There are various software
development life cycle models defined and designed which are followed during
the software development process. These models are also referred as Software
Development Process Models". Each process model follows a Series of steps
unique to its type to ensure success in the process of software development.
Following are the most important and
popular SDLC models followed in the industry &miuns;
- Waterfall Model
- Iterative Model
- Spiral Model
- V-Model
- Big Bang Model
Other related methodologies are
Agile Model, RAD Model, Rapid Application Development and Prototyping Models.
What is Software Testing?
Software testing is defined as an activity to check whether the actual
results match the expected results and to ensure that the software system is
Defect free. It involves execution of a software component or system
component to evaluate one or more properties of interest.
Software testing also helps to identify errors, gaps or missing requirements
in contrary to the actual requirements. It can be either done manually or using
automated tools. Some prefer saying Software testing as a White
Box and Black Box Testing.
In simple terms, Software Testing means Verification of Application Under
Test (AUT).
Why
is Software Testing Important?
Testing is important because
software bugs could be expensive or even dangerous. Software bugs can
potentially cause monetary and human loss, and history is full of such
examples.
- In April 2015, Bloomberg terminal in London crashed due
to software glitch affected more than 300,000 traders on financial
markets. It forced the government to postpone a 3bn pound debt sale.
- Nissan cars have to recall over 1 million cars from the
market due to software failure in the airbag sensory detectors. There has
been reported two accident due to this software failure.
- Starbucks was forced to close about 60 percent of
stores in the U.S and Canada due to software failure in its POS system. At
one point store served coffee for free as they unable to process the
transaction.
- Some of the Amazon’s third party retailers saw their
product price is reduced to 1p due to a software glitch. They were left
with heavy losses.
- Vulnerability in Window 10. This bug enables users to
escape from security sandboxes through a flaw in the win32k system.
- In 2015 fighter plane F-35 fell victim to a software
bug, making it unable to detect targets correctly.
- China Airlines Airbus A300 crashed due to a software
bug on April 26, 1994, killing 264 innocent live
- In 1985, Canada's Therac-25 radiation therapy machine
malfunctioned due to software bug and delivered lethal radiation doses to
patients, leaving 3 people dead and critically injuring 3 others.
- In April of 1999, a software bug caused the failure of
a $1.2 billion military satellite launch, the costliest accident in
history
- In may of 1996, a software bug caused the bank accounts
of 823 customers of a major U.S. bank to be credited with 920 million US
dollars.
Types
of Software Testing
Typically Testing is classified into
three categories.
- Functional Testing
- Non-Functional Testing or Performance Testing
- Maintenance (Regression and Maintenance)
User acceptance testing (UAT)
User
acceptance testing (UAT) is the last phase of the software testing process.
During UAT, actual software users test the software to make sure it can handle
required tasks in real-world scenarios, according to specifications.
·
UAT is one of the final and most
critical software project procedures that must occur before newly developed
software is rolled out to the market.
·
UAT is also known as beta testing,
application testing or end user testing.
UAT is
important because it helps demonstrate that required business functions are
operating in a manner suited to real-world circumstances and usage.
Acceptance tests are useful,
because:
- they capture user requirements in a directly verifiable
way,
- they identify problems which unit or integration tests
might have missed,
- and they provide an overview on how “done” the system
is.
When looking at the process of
software development, we can see that UAT is utilised to identify & verify
client needs.
UNIT TESTING
UNIT TESTING is a level of software testing where
individual units/ components of a software are tested. The purpose is to
validate that each unit of the software performs as designed. A unit is the
smallest testable part of any software. It usually has one or a few inputs and
usually a single output. In procedural programming, a unit may be an individual
program, function, procedure, etc. In object-oriented programming, the smallest
unit is a method, which may belong to a base/ super class, abstract class or
derived/ child class. (Some treat a module of an application as a unit. This is
to be discouraged as there will probably be many individual units within that
module.) Unit testing frameworks, drivers, stubs, and mock/ fake objects
are used to assist in unit testing.
Definition by ISTQB
- unit
testing: See component
testing.
- component
testing: The
testing of individual software components.
Unit Testing Method
It is performed by using the White Box
Testing method.
When is it performed?
Unit Testing is the first level of
software testing and is performed prior to Integration
Testing.
Who performs it?
It is normally performed by software developers themselves or their peers.
In rare cases, it may also be performed by independent software testers.
Unit
Testing Benefits
- Unit testing increases confidence in changing/
maintaining code. If
good unit tests are written and if they are run every time any code is
changed, we will be able to promptly catch any defects
introduced due to the change. Also, if codes are already made less
interdependent to make unit testing possible, the unintended impact of
changes to any code is less.
- Codes are more reusable. In order to make unit testing possible, codes need to
be modular. This means that codes are easier to reuse.
- Development is faster. How? If you do not have unit testing in place, you
write your code and perform that fuzzy ‘developer test’ (You set some
breakpoints, fire up the GUI, provide a few inputs that hopefully hit your
code and hope that you are all set.) But, if you have unit testing in
place, you write the test, write the code and run the test. Writing tests
takes time but the time is compensated by the less amount of time it takes
to run the tests; You need not fire up the GUI and provide all those
inputs. And, of course, unit tests are more reliable than ‘developer
tests’. Development is faster in the long run too. How? The effort
required to find and fix defects found during unit testing is very
less in comparison to the effort required to fix defects found
during system testing or acceptance testing.
- The cost of fixing a defect detected during unit testing
is lesser in comparison to that of defects detected at higher levels. Compare the cost (time, effort, destruction,
humiliation) of a defect detected during acceptance testing or when the
software is live.
- Debugging is easy.
When a test fails, only the latest changes need to be debugged. With
testing at higher levels, changes made over the span of several
days/weeks/months need to be scanned.
- Codes are more reliable. Why? I think there is no need to explain this to a
sane person.
What is Regression Testing?
Regression Testing is defined as a type of software testing to confirm that
a recent program or code change has not adversely affected existing features.
Regression Testing is nothing but a full or partial selection of already
executed test cases which are re-executed to ensure existing functionalities
work fine.
This testing is done to make sure that new code changes should not have side
effects on the existing functionalities. It ensures that the old code still
works once the new code changes are done.
Need
of Regression Testing
Regression Testing is required when
there is a
- Change in requirements and code is modified according
to the requirement
- New feature is added to the software
- Defect fixing
- Performance issue fix
Software maintenance is
an activity which includes enhancements, error corrections, optimization and
deletion of existing features. These modifications may cause the system to work
incorrectly. Therefore, Regression Testing becomes necessary.
Software Base Lining and
Debugging
Baselining is the process
of setting up the common, minimum requirements of an enterprise. This could be
for a group of computers or all the computers in the network. When a new
computer is added to the domain, the common minimum requirements are installed
and applied automatically. This saves a lot of time and effort for the
administrators.
Scenario
Assume, you are managing 500 computers using Desktop Central. All the
computers should have some of the basic software applications like Adobe
Reader, Microsoft Outlook, etc., Since you know the basic requirement, you can
create a baseline for the required software applications and apply it to the
required computers or across the network. This ensures that, whenever a new
computer is added to the domain, the baseline gets applied by default.
Definition of 'Debugging'
Definition:
·
Debugging is the
process of detecting and removing of existing and potential errors (also called
as ‘bugs’) in a software code that can cause it to behave unexpectedly
or crash.
·
To
prevent incorrect operation of a software or system, debugging is used to find
and resolve bugs or defects.
·
When
various subsystems or modules are tightly coupled, debugging becomes
harder as any change in one module may cause more bugs to appear in another. Sometimes
it takes more time to debug a program than to code it.
Description:
To debug a program, user has to
start with a problem, isolate the source code of the problem, and then fix it.
A user of a program must know how to fix the problem as knowledge about problem
analysis is expected. When the bug is fixed, then the software is ready to use.
Debugging tools (called debuggers) are used to identify coding errors at
various development stages. They are used to reproduce the conditions in which
error has occurred, then examine the program state at that time and locate the
cause. Programmers can trace the program execution step-by-step by evaluating
the value of variables and stop the execution wherever required to get the
value of variables or reset the program variables. Some programming language
packages provide a debugger for checking the code for errors while it is being
written at run time.
Data flow diagram (DFD )
https://www.lucidchart.com/pages/data-flow-diagram?a=0
A data flow diagram (DFD ) is a way
of representing a flow of a data of a process
or a system (usually an information system) The DFD also provides
information about the outputs and inputs of each entity and the process itself.
A data flow diagram has no control flow, there are no decision rules and no
loops. Specific operations based on the data can be represented by a flowchart.
A data flow diagram can dive into
progressively more detail by using levels and layers, zeroing in on a
particular piece. DFD levels are numbered 0, 1 or 2, and occasionally go
to even Level 3 or beyond. The necessary level of detail depends on the scope
of what you are trying to accomplish.
- DFD Level 0 is also called a Context Diagram. It’s a
basic overview of the whole system or process being analyzed or modeled.
It’s designed to be an at-a-glance view, showing the system as a single
high-level process, with its relationship to external entities. It should
be easily understood by a wide audience, including stakeholders, business
analysts, data analysts and developers.
·
DFD
Level 1 provides a more detailed breakout of pieces of the Context Level
Diagram. You will highlight the main functions carried out by the system, as
you break down the high-level process of the Context Diagram into its subprocesses.
DFD in software
engineering:
DFD in business analysis:
DFD in business process re-engineering
DFD in agile development:
DFD in system structures:
Context diagram
The first level of Data flow
diagram, know as context diagram, describes the overview
functionalities required by the external entities; it can be decomposed into a
number of sub-level DFDs in hierarchical manner.
Context-Level Diagram
A context diagram gives an overview
and it is the highest level in a data flow diagram, containing only one process
representing the entire system. It should be split into major processes which
give greater detail and each major process may further split to give more
detail.
- All external entities are shown on the context diagram
as well as major data flow to and from them.
- The diagram does not contain any data storage.
- The single process in the context-level diagram,
representing the entire system, can be exploded to include the major
processes of the system in the next level diagram, which is termed as
diagram 0.
·
What is an
Entity Relationship Diagram (ERD)?
·
An entity relationship diagram (ERD)
shows the relationships of entity sets stored in a database. An entity in this
context is an object, a component of data. An entity set is a collection of
similar entities. These entities can have attributes that define its
properties.
·
·
By defining the entities, their
attributes, and showing the relationships between them, an ER diagram
illustrates the logical structure of databases.
·
ER diagrams are used to sketch out
the design of a database.
5 major components
Common Entity Relationship Diagram Symbols
An ER diagram is a means of visualizing how the information a system
produces is related. There are five main components of an ERD:
- Entities, which are represented by rectangles.
An entity is an object or concept about which you want to store
information.
- Actions, which are represented by diamond
shapes, show how two entities share information in the database.
- Attributes, which are represented by ovals. A
key attribute is the unique, distinguishing characteristic of the entity.
For example, an employee's social security number might be the employee's
key attribute.
- Connecting lines, solid lines that connect
attributes to show the relationships of entities in the diagram.
- Cardinality specifies how many instances of an
entity relate to one instance of another entity. Ordinality is also
closely linked to cardinality. While cardinality specifies the occurrences
of a relationship, ordinality describes the relationship as either
mandatory or optional. In other words, cardinality specifies the maximum
number of relationships and ordinality specifies the absolute minimum
number of relationships.
Documentation
Documentation is a set of documents provided on paper, or online,
or on digital
or analog media, such as audio tape
or CDs. Examples are user guides, white papers, on-line help,
quick-reference guides. It is becoming less common to see paper (hard-copy)
documentation. Documentation is distributed via websites, software products,
and other on-line applications.
Report
A document that presents
information in an organized format for a specific audience and purpose.
Although summaries of reports may be delivered orally, complete reports are
almost always in the form of written documents.
April 11, 2025
Structured and object oriented programming
Abstract data type
A useful tool for specifying the logical properties of a data type is the abstract data type or ADT.
Fundamentally, a data type is a collection of values and set of operation on those values.
That collection and those operations form a mathematical construct that may be implemented using a particular hardware or software data structure.
The term “Abstract Data type” refers to the basic mathematical concept that defines the data type.
Formally, An abstract data type is a data declaration packaged together with the operations that are meaningful on the data type.
In other words, we can encapsulate the data and the operation on data and we hide them from user.
It is a mathematical model that contains set of values and function on thoses values without specifying the details of those functions.
Examples of ADT :
1. Linear ADTs:
Stack (last-in, first-out) ADT
Queue (first-in, first-out) ADT
a. Lists ADTs
Arrays
Linked List
Circular List
Doubly Linked List
2. Non-Linear ADTs
a. Trees
Binary Search Tree ADT
b. Heaps
c. Graphs
Undirected
Directed
d. Hash Tables
We can perform following basic operations on ADTs insert(),delete(), search(), findMin(),findMax(),findNext(), findPrevious(), enqueue(), dequeue() etc.
Computer Architecture
RISC/CISC architecture
Comparison between RISC and CISC:
Difference between RISC and CISC