This document provides an introduction to database transactions. It defines a transaction as a collection of database operations executed as a logical unit. Transactions must have the ACID properties of atomicity, consistency, isolation, and durability. The document outlines the basic operations of transactions including begin, read, write, end, commit, and rollback. It describes the states a transaction can be in like active, partially committed, committed, failed, and aborted. Isolation is discussed as ensuring transactions are executed independently without interference from other concurrent transactions. Finally, the role of the scheduler in managing new transactions and instructing the buffer manager is summarized.

1. WELCOME

2. “TRANSACION ”
Submitted By
Mr.Shivpuje Prathnesh.
Mr.Shrangare Pratik.
Mr.Waghmare Pratik
Mr.waghmare Rohit.
Mr.Waghmare Shri.
Under The Guidence of
Miss.Suryawanshi mam

3. INTRODUCTION
 A transaction models the execution of a software procedure constituted by a set of
instructions that may ”read from” and “write on” a database, and that form a single
logical unit. Syntactically, we will assume that every transaction contains: – one “begin”
instruction – one “end” instruction – one among “commit” (confirm what you have done
on the database so far) and “rollback” (undo what you have done on the database so far)
As we will see, each transaction should enjoy a set of properties (called ACID)

4. TRANSACTIONS
transaction is a program including a collection of database
operations, executed as a logical unit of data processing. The
operations performed in a transaction include one or more of
database operations like insert, delete, update or retrieve
data. It is an atomic process that is either performed into
completion entirely or is not performed at all. A transaction
involving only data retrieval without any data update is called
read-only transaction.

5. TRANSACTION OPERATIONS
begin_transaction − A marker that specifies start of transaction
execution.
read_item or write_item − Database operations that may be
interleaved with main memory operations as a part of transaction.
end_transaction − A marker that specifies end of transaction.
commit − A signal to specify that the transaction has been
successfully completed in its entirety and will not be undone.
rollback − A signal to specify that the transaction has been
unsuccessful and so all temporary changes in the database are
undone. A committed transaction cannot be rolled back

6. Active − The initial state where the transaction enters is the active state. The
transaction remains in this state while it is executing read, write or other operations.
Partially Committed − The transaction enters this state after the last statement of the
transaction has been executed.
Committed − The transaction enters this state after successful completion of the
transaction and system checks have issued commit signal.
Failed − The transaction goes from partially committed state or active state to failed
state when it is discovered that normal execution can no longer proceed or system
checks fail.
Aborted − This is the state after the transaction has been rolled back after failure and
the database has been restored to its state that was before the transaction began.
Transaction States

7. ISOLATION OF TRANSACTIONS
 The DBMS deals with this problem by ensuring the so-called
“isolation” property for the transactions This property for a
transaction essentially means that it is executed like it was the
only one in the system, i.e., without concurrent transactions
While isolation is essential, other properties are important as
well.

8. SCHEDULER
The scheduler is part of the transaction manager, and works as follows: –
It deals with new transactions entered into the system, assigning them an
identifier – It instructs the buffer manager so as to read and write on the
DB according to a particular sequence – It is NOT concerned with specific
operations on the local store of transactions, nor with constraints on the
order of executions of transactions. The last conditions means that every
order by which transactions are entered into the system is acceptable to
the schedule.

9. THANK YOU…