Objective of the presentation is to discuss about Transaction Model and Improve performance of transaction processing

1. Chapter III
Concurrency Control
Ramkumar Lakshminarayanan

2.  Transaction Model
 Improve performance of transaction processing
Objective

3.  Lost Updates
 Inconsistent Retrievals / incorrect summary
 Uncommitted Dependency /Dirty Read
Concurrency Anomalies

4.  Two or more transactions trying to change (write) the
same part of the database.
Lost Update

5. Dirty Read

6.  A transaction reads an object updated by another
transaction before the other transaction commits
(that later fails)
 The value used by the second transaction is :
Phantom Value
Uncommitted Dependency
(Dirty Read)

7.  Transactions
reads several
values, but
another
transaction
updates some
of the values
while the first
transaction is
still executing.
Inconsistent Retrieval /
Incorrect Summary

8.  Lock method sets an exclusive lock on the item, and
refreshes any unchanged cache data for the item.
 Item get unlocked when the transaction ended by the
abort or commit method.
Lock Method

9.  Will request for the lock before performing read/write
operation.
 Will not allow to perform the read/write without
getting the lock.
 Lock manager is responsible for managing all locks in
the system
Locking Protocol

10.  Lock is a variable attached with any resource to
control resource access by its users.
Lock

11.  Exclusive (X Lock) (Write Lock) - when the
transaction intension is to write.
 One transaction can have this lock.
Exclusive (X Lock)

12.  Shared (S Lock) (Read Lock) – are locks for read only.
Shared (S Lock)

13. Next Class – Dead Lock.