transaction management

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TRANSACTION MANAGEMENT :

TRANSACTION MANAGEMENT Presented by m.n.v . peddi raju Roll no 17 ) There are three side effects of acid. Enhanced long term memory, decreased short term memory, and I forget the third. - Timothy Leary

Introduction :

Introduction A transaction includes one or more database access operations which include insertion,deletion , modification ,or retrival operations.

Definition:

Definition Collection of operations that form a single logical unit of work is called a transaction.

Acid properties of transaction:

Acid properties of transaction They are useful in order to avoid failures during concurrent access to a database. ACID IS acronym for Atomicity Consistency Isolation Durability

Atomicity:

Atomicity Atomicity states that database modifications must follow an “all or nothing” rule If one part of transaction fails,the entire transaction fails The database system keeps track( ondisk ) of old values and if the transaction doesn't complete its execution it restores the old values and appears as it was never performed It is handled by a component called transaction management component

consistency:

consistency If the database is consistent before an execution of the transaction,the database remains consistent after the execution of transaction Only valid data must be written to the data base otherwise it will be roll backed Ensuring consistency is the responsibility of application programmer who codes the transaction

Isolation :

Isolation Every transaction should be kept unaware of other transactions and execute independently. Intermediate results generated by the transactions must not be available to other transaction Responsible component concurrency control component A way to avoid the problem is to execute serially (practically not possible)

durability:

durability Data remains consistent state even after failure This is due to by loading modified data into disk It enables a system to recover after system crash Handled by recovery management component of dbms

Types of locks Shared / Exclusive Locks:

Types of locks Shared / Exclusive Locks Shared Lock – Concurrent Transactions are granted READ access on the basis of a common lock Exclusive Lock – Access is reserved for the transaction that locked the object

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