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Friday, May 15, 2020

May 15, 2020

BACK UP AND RECOVERY

BACK UP AND RECOVERY: 

Backup and recovery of database



DATABASE MANAGEMENT SYSTEM

 
8. BACK UP AND RECOVERY:
Database backups; why plan backups?
Hardware protection and redundancy
Transaction logs.
Importance of backups
Database recovery

Introduction to database backup: -

1. An objectionable failure of data where a stable, secondary storage device gets corrupt and this causes lost of all valuable data that is stored inside them.
2. To overcome from that situation we need backup of data in other word we can say that database backup is storage of data that means the copy of the data.
3. Database backup is a type of safeguard against unexpected loss of data and application errors.
4. The protection of data against data loss is done by database backup.
5. Suppose due to some issue or any unexpected condition the original data has been lost, then by using database backup we can easily reconstruct our data.
6. Database backup is done through replication and can be done for a database and its server.


Why plan for backups?

Before we know why we plan for backups first we have to know about some causes of failures.
As we know that database includes a huge amount of data and transaction of data and the system crashes or failure, then it is very difficult to recover database.
Some common causes of failures of data: -

1. System crash: -
a. When there is a hardware or software failure or external failure like power failure these failures are known as system crash.
b. In system crash the data which are in the secondary storage in not affected because lots of integrity of database, checkpoint prevents the loss of data from the secondary memory.

2. Transaction failure: -
a. Due to logical errors in the code transaction failure occur which affected only few tables or processes.
b. Transaction failure occur when there are system errors i.e. deadlock or unavailability of system resources.c. There is an ACID property in each transaction and if we fail to maintain the ACID properties are causes the failure of database.

3. Network failure: -
a. When a client-server configuration or distributed database system are connected by communication systems the network failure occurs.

4. Disk failure: -
a. Disk failure occurs when there are issues with hard disks some of them are formation of disks from bad sectors, disk head crash, and unavailability of disk like that.

5. Media failure: -
a. The most dangerous failure is media failure because of it take more time to recover than any other kind of failure.
b. The example of media failure is disk controller or disk head crash.

If we want our important data will remain safe and secure, we have to plan for data backups. If any of the failure occur and there is loss of important data if we have backup of our data then we can easily get them.

Types of backups: -

The backup are dividing into two types: -
       1. Physical backup: -
a. Backups of the physical files used in storing and recovering your database such as data files, control files, archived redo logs, and log files are comes under physical backups.
b. Physical backup is a copy of files storing database information to some other location i.e. disk, magnetic tape.
c. The foundations of the recovery mechanism in the database are physical backups.

      2. Logical backups: -
a. Logical data which is extracted from a database is logical backup.
b. Logical backup includes backup of data like views, procedures, functions, tables.
c. Logical backup is a useful supplement to physical backups in many circumstances. Logical backup provides only structural information.

Hardware protection: -

1. Hardware protection or hardware security is a penetrability protection that comes in the form of a physical device rather than software that is installed on the hardware of a computer system.
2.  The term Hardware protection also refers to the protection of the physical system from the harm.
3. Hardware protection can belong to a device used to scan a system or monitor network traffic.
4. Hardware protection can provide more robust security than software is capable and it provide an additional layer of security for important systems.
5. If anyone wants to assess the security of a hardware device, it’s become necessary to consider penetrability existing from its manufacture as well as other potential sources such as code and the device’s data I/O on a network.
6. Systems which controls the color and intensity of lights in Wi-Fi LED foe a dwelling they not require much security.

Redundancy: -

1. Data redundancy is an organization of data issue that allows the unnecessary duplication of data in your database.
2. Data redundancy means having more than one copies of data or multiple data in same database
3. A change or modification in redundant data requires that you make changes to multiple fields of a database.
4. In a database data redundancy can be found, which is an organized collection of structured data that’s stored by a computer system or the cloud?
5. Example, suppose a retailer entered the products they stick in their database by mistake same product gets entered twice then data redundancy take place.
6. Some advantages of Data redundancy are as follow: -
a. Alternative data backup method: -
Data redundancies offer an extra layer of protection and activate the backup by replicating data to another system.
b. Better data security: -
If you have same data stored in two or more separate places it can protect an organization in the event of a cyber attack or beach, beach is an event that can result in lost time and money as well as damaged reputation.
c. Faster data access and updates: -
If our data is redundant, employees of our company enjoy fast access and quick updates because the necessary information’s are available on more than one system i.e. multiple system
d.  Improved data reliability: -
                                                                                Reliable data is complete and accurate. Organizations can use data redundancy to double check data and confirm data is correct and complete.
7. Some disadvantages of data redundancy are as follows: -
a. Increase in data corruption: -
When data becomes damaged because of errors in writing, reading, storage, and processing then data corruption is occurred.
b. Increase database size: -
Data redundancy can increase the size of data and complexity of database.
c. Increase in cost: -
Due to Data redundancy more data is created it causes increase in cost of storage which causes a serious issue in an organization.
d. Possible data inconsistency: -
Data redundancy occurs when the same data exists in more than one place or multiple places, data inconsistency occurs when the same data exists in different format in multiple tables.
Transaction logs: -
1. A database management system (DBMS) uses a transaction log which keeps track of all transactions that are used to update the database.
2. The information stored in the transaction log is used by the Database management system (DBMS) for a requirement of recovery which triggered by a ROLLBACK statement.
3. Relational DBMS’s use the transaction log to recover a database forward to a currently consistence state.
4. DBMS executes transaction log to modify the database and it can also automatically updates the transaction log.
5. The data which is stored by transaction log: -
a. There is a record for the beginning of the transaction.
b. Component for each transaction i.e. SQL statement.
c. Which operation is performed such as updates, insert, delete.
d. Name of the objects which are affected by the transaction i.e. name of the table.
e. For the same transaction there is a pointer to the previous and next transaction.
6. Entries of the logs are sequential in nature and transaction logs are split up to small field called virtual log files.
7. When a virtual log file is full the transactions are automatically move to the next virtual log file.








Importance of backup: -
1. Backup helps against failure of media, software, operating system and another kind of failures such as serious data crash.
2. Backup also determines the speed and success of the recovery.
3. Backup extracts data from physical storage i.e. data from disk to tape, OS is an example of physical backup.
4. Backup extracts data using SQL form the database and store it as a binary file.
5. Backup like logical backup is used to restore database objects into the database.
Database recovery:  -
1. The process of restoring a database to the correct state in the event of a failure is called recovery.
2. Recovery insures that the databases are reliable and remains in consistent state in case of a failure.
3. Data recovery is the process of restoring the database and the data’s which are in consistent state which may include restoring lost data up to the point of the event i.e.  System crash.
4. Recovery of database are classified into two parts they are as follow: -
a. Rolling forward: -It applies records can be redoing to the corresponding data blocks.
b. Rolling back: -It applies rollback segments to the data files. Rolling back is stored in transaction tables.
5. When a DBMS recovers from a crash, it should maintain the following steps: -
a. To check the states of all transactions those are being executed.
b. The DBMS must ensure the atomicity of the transaction if a transaction in the middle of some operation.
c. Recover must check whether the transaction can be completed now or it needs to be rolled back.
d. If the transaction in an inconsistent state no transaction would be allowed to leave the DBMS

Log based recovery: -
   
1. The sequence of records that maintain the records of actions performed by a transaction is known as Log.
2. Log-based recovery of each transaction in maintained in some stable storage and if any failure occurs it can be recovered from there to recovery database.
3. The information about the transaction being executed, values that have been modified and transaction state is contain by the log.
4. The below logs are written for transaction: -
Log 1: writes “START” log to initiated a transaction
Log :
Log 2: Transaction modifies the address from one place to another, let “Delhi” to “Bihar”.
Log:
Log 3: Transaction is completed, the log indices the end of the transaction.
Log:
We can create log files and updating database by using this two method: -
1. Deferred database modification
2.  Immediate database modification




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Thursday, May 14, 2020

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Class and Objects
May 14, 2020

Class and Objects

C++ Classes and Objects

Class:- A class in C++ is the building block, that leads to Object-Oriented programming. It is a user-defined data type, which holds its own data members and member functions, which can be accessed and used by creating an instance of that class. A C++ class is like a blueprint for an object.

Class...

  • Class is a collection of data member and member function in a single unit .
  • Class is a keyword which is used for declare a class .
  • The member of the class is private  by default.
  • Class is used for providing high security.
  • Class is used in large program and it takes more memory space.
  • Syntax :
 Class class_name
 {
   Private :
     ...................
     ......…..........
   Public :
     ...................
     ...................
};

* Object...

  • Object is an instance of a class .
  • We can pass the value directly through the object .
  • Syntax :  class_name object_name ;

Define C++ Objects

A class provides the blueprints for objects, so basically an object is created from a class. We declare objects of a class with exactly the same sort of declaration that we declare variables of basic types. Following statements declare two objects of class Box −
Box Box1;          // Declare Box1 of type Box
Box Box2;          // Declare Box2 of type Box
Both of the objects Box1 and Box2 will have their own copy of data members.

The classes are the most important feature of C++ that leads to Object Oriented programming. Class is a user defined data type, which holds its own data members and member functions, which can be accessed and used by creating instance of that class.
The variables inside class definition are called as data members and the functions are called member functions.
For Example: Consider the Class of Cars. There may be many cars with different names and brand but all of them will share some common properties like all of them will have 4 wheels, Speed Limit, Mileage range etc. So here, Car is the class and wheels, speed limits, mileage are their properties.
  • A Class is a user defined data-type which has data members and member functions.
  • Data members are the data variables and member functions are the functions used to manipulate these variables and together these data members and member functions defines the properties and behavior of the objects in a Class.
  • In the above example of class Car, the data member will be speed limit, mileage etc and member functions can be apply brakes, increase speed etc.
An Object is an instance of a Class. When a class is defined, no memory is allocated but when it is instantiated (i.e. an object is created) memory is allocated.

Concept of class with example

Example of class in easy way to understand In C++.

#include 
#include
using namespace std;

// Class Declaration

class technical {
    
public:

    
    string name;
    int number;
};

int main() {
    // Object created
    technical obj;
    cout << "Enter the Name :";
    cin >> obj.name;

    cout << "Enter the Number :";
    cin >> obj.number;

    cout << obj.name <<" : "<< obj.number << endl;

    getch();
    return 0;
}

Output

Enter the Name :point
Enter the Number :100
point : 100
Defining Class and Declaring Objects
A class is defined in C++ using keyword class followed by the name of class. The body of class is defined inside the curly brackets and terminated by a semicolon at the end.classes-and-objects-in-c
Declaring Objects: When a class is defined, only the specification for the object is defined; no memory or storage is allocated. To use the data and access functions defined in the class, you need to create objects.
Syntax:
ClassName ObjectName;
Accessing data members and member functions: The data members and member functions of class can be accessed using the dot(‘.’) operator with the object. For example if the name of object is obj and you want to access the member function with the name printName() then you will have to write obj.printName() .
Accessing Data Members
The public data members are also accessed in the same way given however the private data members are not allowed to be accessed directly by the object. Accessing a data member depends solely on the access control of that data member.
This access control is given by Access modifiers in C++. There are three access modifiers : public, private and protected.
// C++ program to demonstrate 
// accessing of data members 
  
#include
using namespace std;
class technical point
{
    // Access specifier
    public:
  
    // Data Members
    string technicalpointname;
  
    // Member Functions()
    void printname()
    {
       cout << "technicalpoint is: " << technicalpoint;
    }
};
  
int main() {
  
    // Declare an object of class geeks
    technicalpoint obj1;
  
    // accessing data member
    obj1.technicalpointname = "Learning";
  
    // accessing member function
    obj1.printname();
    return 0;
}
Output:
technicalpointname is: Learning
Member Functions in Classes
There are 2 ways to define a member function:
  • Inside class definition
  • Outside class definition
To define a member function outside the class definition we have to use the scope resolution :: operator along with class name and function name.
C++ program to demonstrate function 
// declaration outside class
  
#include
using namespace std;
class Geeks
{
    public:
    string geekname;
    int id;
      
    // printname is not defined inside class definition
    void printname();
      
    // printid is defined inside class definition
    void printid()
    {
        cout << "Geek id is: " << id;
    }
};
  
// Definition of printname using scope resolution operator ::
void Geeks::printname()
{
    cout << "Geekname is: " << geekname; 
}
int main() {
      
    Geeks obj1;
    obj1.geekname = "xyz";
    obj1.id=15;
      
    // call printname()
    obj1.printname();
    cout << endl;
      
    // call printid()
    obj1.printid();
    return 0;
}
Output:
Geekname is: xyz
Geek id is: 15
Note that all the member functions defined inside the class definition are by default inline, but you can also make any non-class function inline by using keyword inline with them. Inline functions are actual functions, which are copied everywhere during compilation, like pre-processor macro, so the overhead of function calling is reduced.
Note: Declaring a friend function is a way to give private access to a non-member function.

c++ - Returning object from function

A function can also return objects either by value or by reference. When an object is returned by value from a function, a temporary object is created within the function, which holds the return value. This value is further assigned to another object in the calling function
The syntax for defining a function that returns an object by value is
class_name function_name (parameter_list)
{
// body of the function
}
To understand the concept of returning an object by value from a function, consider this example.

Example of Passing object & Returning object

#include
 #include

 class Rectangle
 {
  int L,B;

 Rectangle(int l,int b)
 {
  L = l;
  B = b;
 }

 Rectangle()
 {
  L = 0;
  B = 0;
 }

 Rectangle Sum(Rectangle Rec)        //function  1
 {

  Rectangle temp;

  temp.L = L + Rec.L;     //Statement  1
  temp.B = B + Rec.B;     //Statement  2

  return temp;
 }

 void Display()
 {
  cout<<"\nLength : "<//Statement  3
cout<<"\n\nValues of Rectangle 3 : "; R3.Display(); } Output : Values of Rectangle 1 : Length : 5 Breadth : 7 Values of Rectangle 2 : Length : 2 Breadth : 3 Values of Rectangle 3 : Length : 7 Breadth : 10
In statement 3, object R1 is calling member function Sum and passing object R2 as argument. Function 1 is receiving values of R2 in Rec. In statement 1 L is length of calling object R1 and Rec.L is length of object R2.
Both statement 1 and 2 is adding the length and breadth of Rectangle 1 and 2 respectively and assigning the result to object temp.
Statement 3 is receiving the values of object temp in object R3.
Structure vs class in C++
In C++, a structure is the same as a class except for a few differences. The most important of them is security. A Structure is not secure and cannot hide its implementation details from the end user while a class is secure and can hide its programming and designing details. Following are the points that expound on this difference:
1) Members of a class are private by default and members of a struct are public by default.
For example program 1 fails in compilation and program 2 works fine.
// Program 1
#include
  
class Test {
    int x; // x is private
};
int main()
{
  Test t;
  t.x = 20; // compiler error because x is private
  getchar();
  return 0;
}


// Program 2
#include
  
struct Test {
    int x; // x is public
};
int main()
{
  Test t;
  t.x = 20; // works fine because x is public
  getchar();
  return 0;
}
2) When deriving a struct from a class/struct, default access-specifier for a base class/struct is public. And when deriving a class, default access specifier is private.
For example program 3 fails in compilation and program 4 works fine.
   
// Program 3
#include
  
class Base {
public:
    int x;
};
  
class Derived : Base { }; // is equilalent to class Derived : private Base {}
  
int main()
{
  Derived d;
  d.x = 20; // compiler error becuase inheritance is private
  getchar();
  return 0;
}


// Program 4
#include
  
class Base {
public:
    int x;
};
  
struct Derived : Base { }; // is equilalent to struct Derived : public Base {}
  
int main()
{
  Derived d;
  d.x = 20; // works fine becuase inheritance is public
  getchar();
  return 0;
}
difference between class and structure

Class
  1. To define class we will use “class” keyword.
  2. When we initiate a class it will be allocate into heap memory.
  3. To create an object for class we have to use new operator.
  4. Class will support inheritance.
  5. Class can contain destructor.
  6. Class are reference type.
Structure
  1. To define structure we will use “struct” keyword.
  2. When we initiate a structure it will be allocate into stack memory.
  3. To create an object for structure we don't require to use new operator.
  4. Structure will not support inheritance.
  5. Structure can't contain destructor.
  6. Structure are value type.


Array of Object in C++



An object of class represents a single record in memory, if we want more than one record of class type, we have to create an array of class or object. As we know, an array is a collection of similar type, therefore an array can be a collection of class type.

Syntax for Array of object

class class-name
              {
                     datatype var1;
                     datatype var2;
                     - - - - - - - - - -
                     datatype varN;

                     method1();
                     method2();
                     - - - - - - - - - -
                     methodN();
              };

              class-name obj[ size ];

Example for Array of object

       #include
       #include

       class Employee
       {
              int Id;
              char Name[25];
              int Age;
              long Salary;

              public:
              void GetData()           //Statement 1 : Defining GetData()
              {
                    cout<<"\n\tEnter Employee Id : ";
                    cin>>Id;

                    cout<<"\n\tEnter Employee Name : ";
                    cin>>Name;

                    cout<<"\n\tEnter Employee Age : ";
                    cin>>Age;

                    cout<<"\n\tEnter Employee Salary : ";
                    cin>>Salary;
              }

              void PutData()           //Statement 2 : Defining PutData()
              {
                    cout<<"\n"< Output :
Enter details of 1 Employee
 Enter Employee Id : 101
 Enter Employee Name : Mohsin
 Enter Employee Age : 20
 Enter Employee Salary : 45000
 Enter details of 2 Employee
 Enter Employee Id : 102
 Enter Employee Name : Naim
 Enter Employee Age : 20
 Enter Employee Salary : 51000
 Enter details of 3 Employee
 Enter Employee Id : 103
 Enter Employee Name : Mirza Ali
 Enter Employee Age : 21
 Enter Employee Salary : 47000
 Details of Employees
 101 Mohsin 20 45000 1
 02 Naim 20 51000
 103 Mirza Ali 28 47000


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