Shadow paging is a database recovery technique that uses two page tables - a current page table and a shadow page table. During transaction execution, updates are made to copies of pages in the shadow page table rather than directly updating pages. If a crash occurs, the database can be recovered by freeing the modified pages and using the unchanged shadow page table. Shadow paging reduces log overhead during recovery compared to log-based techniques but has disadvantages like increased data fragmentation and higher commit overhead.

1. Vijaya priya p
I-Msc(cs)

2. Shadow paging
 Shadow paging is an alternative to logbased
crash recovery this scheme is useful if
Transaction execute serially.
 Main two page tables during lifetime of a
Taransaction the current page table and
The shadow page table.
 Advanced based recovery technique used
to recover database.

3. Shadow page is never modified during
execution.
To start with , both the page tables are identical.
Only current page table is used for data item
Accesses during execution of the transaction.
Whenever any page is about to be written for
The first time.
 a copy of this page is made on to an
Unused page.
 the current page table is then made to point
Point to the copy.

4.  The update is performed on the copy.
directory
 Current directory
 Shadow directory
 During the transaction execution, shadow
directory is never modified.
Shadow page recovery
 Free the modified database pages
 Discard the current directory

6. Shadow paging recovery technique

7. Advantage
 Over log- based techniques . The overhead
Of log record output is eliminated , and
Recovery from crashes is significantly faster.
 However, there are drawbacks to the shadow-
Page technique.
 Commit overhead
 Data fragementation
 Garbage collection

8. disadvantage
 Increased data fragmentation on disk
(Reduced level of data clustering.)
 Need for periodic ‘garbage’ collection or
compaction to reclaim fragmented and hence
‘ inaccesssible ’ data blocks on disk.
 Commit overhead is high even with above
Extension
(need to flush every updated page, and page
table)

9.  Data gets fragmented (related pages get
separated on disk).
 After every transaction completion , the
database pages containing old version of
modified data need to be garbage collected.

10. Shadow page model
UNSER TRANSACTION: It is user
interface
Through which the user fires its query.
This query is send to the database
management system(DBMS).
DBMS : the dbms consist of the three
parts. the file transfer to the query
processor,

11. Query processor :
It parse the query and convert it into
tokens and check for the syntax and
semantic errors.
Transaction manager :
If the query parsed by query processor is
correct then, according to the query the
Transaction are generated and executed.
Data manager:
This unit manages the data of our database .it
interact with the memory unit of device.

12. Buffer management
 The buffer manager is the software layer
That is responsible for bringing pages from
Physical disk to main memory as needed.
 The buffer manages the available main memo
By the dividing the main memory into a
Collection of pages ,which we called as buffer
pool.
 Database buffers are grouped in an area of
Memory called the buffer pool.

13.  The main memory pages in the buffer pool
are called frames.
 A buffer pool in the area of main memory that
Has been allocated by the database manager
 Buffer manager controls main memory
directly

14. Database buffering
 Database is stored in disk.
 For read and write operation database must
reside in memory.
Force policy:
Modified blocks is output to disk once a
Transaction commits.
No-force policy:
Modified blocks is not output to disk immediately
A transaction commits .

15. No –steal policy:
Blocks modified by a transaction that is still
active should not be written to disk.
Steal-policy:
Modified blocks written to disk even if
Transaction has not committed.

16. Log - record buffering
 High overhead on system execution for the
Following reasons.
 Typically ,output to stable storage is in units
of blocks, in most cases. A log record is much
Smaller then a block.
 Thus , the output of each log record translate
To a much larger output at the physical level

17. Oracle
&
Microsoft SQL
server

18. Oracle
 Full form of oracle is Oak RidgeAutomatic
Computer and Logical Engine (Oracle).
 oracle database is an object-relational databas
Management system produced and marketed by
Oracle corporation.
 According to gartner , oracle owned nearly 50%
Of the RDBMS market in 2011

19.  Oracle corporation was the first company to
Develop a commercial –level version of SQL
That was designed to multiple data in a RDBMS
using queries and joins.
 Oracle provides enhanced database security
User authentication is performed using global
Roles in addition to location , username and
Password.

20.  Oracle database support and uses XML
Oracle supports 4 different character data types
NamelyCHAR,VARCHAR2, NCHAR,NVARCHAR2
 It offers many backup mechanisms including
 Hot backup, backup, import, export and many
others.

21. Oracle editions

22. Enterprise edition
Most powerful
With vast array of tools
For large corporation
Standard edition
Basic database management
Lower cost
For SME corporation

23. Standard edition one
Designed for single CPU server
Cost effective
For small business
Express edition
Entry level
Small footprint database

24. History of oracle
In 1970- Dr E.F. Codd ‘ published ‘relational
Model for data’
In 1970-IBM developed SEQUEL(structured
english query language )
In 1977- oracle corporation introduced oracle
database (oracle 11g)

25. Oracle overview

26. Foundation of oracle

27. Microsoft SQL server
 Microsoft SQL server is a RDBMS (relational
Database management system) created by
microsoft.
 It is used as a central location to save and
Obtain data needed for applications. It uses
SQL (structured query language) for queries
that store or retrieve data.
(Structured query language)

28.  mysql is an open source and free to download
And installation .
 Mysql database do not support XML
 Mysql supports only two character types namely
CHAR and VARCHAR.
 It has only 2 backup mechanism namely
mysqlhotcopy & mysqldump

29. SQL database

30. SQL-server storage structure
Following are the units of storage
structure in SQL server.
 Database files
 Extents
 pages

31. Pages and extents