Module 2: Database
Architecture
Overview
Schema and Data Structure (Objects)
Storage Architecture
 Data Blocks, Extents, and Segments
 Storage Allocation
 Managing Extents and Pages
 Tablespaces and Datafiles
 SQL Server Data Files
 Mapping of Tablespaces and Filegroups
Logging Model
Data Dictionary
Schema and Data Structures (Objects)
Schema – a collection of objects owned by a database user
Schemas in SQL Server provide logical separation of objects,
similar to Oracle’s schema
Comparison of Core Schema and Data Structures (Objects)
Oracle
SQL Server
Table
Table
Index
Index
View
View
Synonym
Synonym
Sequence
Sequence
Procedure
Stored Procedure
Function
Function
Package
N/A
Queue in Streams Advanced Queuing
Service Broker Queue
Object Type
Type
XML DB
XML Schema Collection & data type
Storage Architecture
Database storage architecture includes physical and logical structures
Physical structures are data files, log files, and operating system blocks
Logical structures are subdivisions of data files used to manage storage
space
Data File
Data File
Data File
Data File
Data File
Data File
Temporary Tablespace Groups
Tablespace
Tablespace
Filegroup
Filegroup
Segment
Segment
Heap/Index
Heap/Index
Extent
Extent
Extent
Extent
Extent
Extent
Extent
Blocks
Blocks
Blocks
Blocks
Pages
Pages
Pages
Data Blocks, Extents, and Segments
Structure
Oracle
SQL Server 2012
Smallest unit of
logical storage
Block
Page
Block size
Variable
8 KB fixed
Storage allocation
Performed in multiple
blocks; are ‘extents’
Performed in multiple
pages; are ‘extents’
Extent size
Variable
64 KB fixed
Segment
Any logical structure
that is allocated
storage
Allocation unit
Storage Allocation
2K
block
2K
block
2K
2K
block 6 x 2K
block
= 12K
8K
block
8K
block
8K
block
2K
block
2K
block
2K
block
EXTENT
2K
block
8K
block
8K
block
8K 8 x 8K2K
= 64K
block EXTENT
block
2K
block
2K
block
2K
block
2K
block
8K
block
8K
block
8K
block
2K
block
2K
block
2K
block
2K
block
2K
block
8K
block
8K
block
8K
block
2K
block
2K
block
2K
block
2K
block
2K
block
8K
block
8K
block
8K
block
2K
block
2K
block
2K 8 x 2K
2K= 16K 2K
block EXTENT
block
block
8K
block
8K
block
= 64K
8K 8 x 8K2K
block EXTENT
block
2K
block
2K
block
2K
block
2K
block
8K
block
8K
block
8K
block
2K
block
2K
block
2K
block
2K
block
2K
block
8K
block
8K
block
8K
block
2K
block
Oracle
12K + 16K = 28K
SEGMENT
(Table/Index)
2K
block
64K + 64K =
128K
HEAP/INDEX
SQL Server
Fundamental difference in storage allocation between
Oracle and SQL Server
Managing Extents and Pages
In Oracle, each extent is dedicated to an allocated
object. In SQL Server, the equivalent is a uniform extent.
SQL Server uses mixed extents: pages are allocated to
objects with less than 8 blocks of data
Similar to the Oracle bitmap functionality used to
manage free space and extent allocation, SQL Server
uses the Global Allocation Map (GAM) and Shared
Global Allocation Map (SGAM)
Oracle keeps track of extents using extent allocation
maps
Managing Extents and Pages (Continued)
File Header Extent
Extents in
SQL Server
GAM Bit
Setting
SGAM Bit
Setting
Free, not being used
1
0
Uniform extent, or full mixed
extent
0
0
Mixed extent with free pages
0
1
Current Use of Extent
GAMs and SGAMs
Tablespaces and Datafiles
Oracle and SQL Server store data in datafiles
The largest logical storage structure in Oracle is a
tablespace
The largest logical storage structure in SQL Server is a
filegroup
Tablespaces/filegroups are used to group application
objects
Tablespaces/filegroups optimize administration of
datafiles
SQL Server Data Files
Three file types supported by SQL Server:
Primary Data Files
Secondary Data
Files
Log Data Files
Demonstration: Working with Filegroups and
Data Structures
Demonstration:
Working with Filegroups and Data
Structures
Mapping of Tablespaces and Filegroups
System Tablespace
SysAux Tablespace
Temporary Tablespace
Data file
Data file
Log file
Data file
Data file
Data file
Log file
Resource DB
Data file
Log file
TempDB
Data file
Log file
Model DB
Data file
Log file
MSDB
Tablespace Group
Data file
Data file
BigFile Tablespace
User Data Tablespace
Data file
Data file
Data file
Data file
Data file
User Database
User Index Tablespace
Data file
Data file
Data file
Data file
Undo Tablespace
Data file
Data file
Data file
Data file
Redo Log Files
Master DB
Data file
Redo Log
Redo Log
Redo Log
Oracle Database Instance
Log file
SQL Server Instance
User DB
Data FG
Index FG
Log File(s)
Demonstration: Viewing an Instance’s System
Databases
Demonstration:
Viewing an Instance’s System Databases
Logging Model
Oracle uses online redo logs to record changes made to
the database by transactions and undo segments to
capture the ‘before image’ of data
SQL Server implements both of these functions using
transaction logs. Each transaction record contains the
undo and redo image of the transaction.
Data Dictionary
In Oracle the data dictionary is stored under the SYS schema in the
SYSTEM tablespace
In SQL Server the data dictionary consists of:
 Catalog View—the best way to access system metadata
 Backward Compatibility Views—All system tables from previous
releases are provided as backward compatibility views
 Dynamic Management Views—to view the current state of the SQL
Server system. Provide real-time snapshots of internal memory
structures indicating the server state.
 INFORMATION_SCHEMA views—SQL-99 method to view system
metadata
SQL Server’s Resource database contains the metadata for system
stored procedures
Demonstration: View the Data Dictionary
Demonstration:
View the Data Dictionary
Review
Defined schema and identified core schema objects
Examined the storage architecture and its physical
(datafiles, logfiles, and so on) and logical structures
(blocks, extents, segments, and tablespaces)
Defined the hierarchy in the logical structures
Compared Oracle and SQL Server in terms of schema
vs. databases, and tablespaces vs. filegroups
Examined the structures used in the implementation of
the logging model (redo logs and rollback segments in
Oracle vs. transaction logs in SQL Server)
Brief look at the location and composition of the data
dictionary/system catalog