SQL Transaction

1.What is a transaction
Simply it groups of database quires.
A database transaction symbolizes a unit of work performed(Operations:Read Write) within a database management system (or similar system) against a database, and treated in a coherent and reliable way independent of other transactions.

2.why do we need transaction
Group of read write operation;which independent from other operations. Do not execute part of  transaction.If execute all or none.
Eg:-Credit debit operation in ATM management system.

3.Serial Schedule Transaction Vs Serializable Schedule transaction

*A complete schedule* is a schedule that contains either an abort or a commit for each transaction in the set.
*A serial schedule* is a schedule that the actions of different transactions are not interleaved, that is transactions are executed from start to finish, one by one.
*A serializable schedule* over a set S of committed transactions is a schedule whose effect on any consistent database instance is guaranteed to be identical to that of some complete serial schedule over S.

Body
The serial schedule is a type of schedule where one transaction is executed completely before starting another transaction.

The serializable schedule is a schedule which run transaction with mixing,but the artifact is as same as to the serial schedule.  

4.Concurrency VS Multi tasking VS Multi tasking 

Parallelism
Doing several task at one time .for that must have multiple cores.

Multi tasking 
the fact of two or more events or circumstances happening or existing at the same time.(Time bound specified)

Concurrency
In computer science, concurrency is the ability of different parts or units of a program, algorithm, or problem to be executed out-of-order or in partial order, without affecting the final outcome.(Time bound not specified)
No sequential execution.
Same artifact the sequential execution.

5.ACID
A transaction in a database system must maintain Atomicity, Consistency, Isolation, and Durability. In order to ensure accuracy, completeness, and data integrity(data integrity refers to the accuracy).


ACID Properties in Databases - DEV

A-Transaction will proceed nothing.Nor Fuzzy state

C-Depend on the developer.Developer must validate data.

I-Interleave transaction isolate each & every another transaction
Eg:-In the banking ATM system has thousand of transaction in the given time.So system must proceed the without any lagging.So ATM system proceed all thousand transaction part by part mixing in concurrent manner.But the output of each & every transaction will separate from another transactions.So we can predict the final outcome of the transaction.

D-If the system crashed halfway in the transaction, DBMS data must have in the previous state before the transaction .

If the transaction will happen we called that commit nor abort. write-ahead logging (WAL) is a family of techniques for providing atomicity and durability (two of the ACID properties) in database systems. 
ARIES(Algorithm for Recovery and Isolation Exploiting Semantics) uses logs to record the progress of transactions and their actions which cause changes to recoverable data objects.

6.Responsibility
C- developer
AID-DBMs
AD-recovery manager

7.Transaction using JAVA

//We apply transaction for the connection
Connection connection = DBConnection.getInstance().getConnection();

    try {
      //By default autocommit "true",to execute as whole code set as "false"
      connection.setAutoCommit(false);

       //Code to be executed
       //connection.rollback(); add if there is any return statement inide the the methods

      connection.commit();//Write data to the data base



    } catch (Throwable ex) {//Use to handle both error & exception
      ex.printStackTrace();
      try {
        connection.rollback();
      } catch (SQLException throwables) {
        throwables.printStackTrace();
      }
    }finally {//finally block run in the method return situation 
      try {
        connection.setAutoCommit(true);//setAutoCommit(true) will executing if program execute or not
      } catch (SQLException throwables) {
        throwables.printStackTrace();
      }
    }

Before commit all transaction detail will store in the buffer in the Server side input buffer.but if connection lost ,all buffered data will lose





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