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 Index View Synonym Sequence Identity Columns Procedure Stored Procedure Function Package N/A Queue in Streams Advanced Queuing Service Broker Queue Object Type Type XML DB XML Schema Collection

Temporary Tablespace Groups 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 Physical Data File Data File Data File Data File Data File Data File Temporary Tablespace Groups Tablespace Tablespace Filegroup Filegroup Logical Segment Segment Heap/Index Heap/Index Extent Extent Extent Extent Extent Extent Extent Blocks Blocks Blocks Blocks Pages Pages Pages ORACLE Sql sERVER

Data Blocks, Extents, and Segments Structure Oracle SQL Server 2008 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 64 KB fixed Segment Any logical structure that is allocated storage No equivalent structure

Storage Allocation 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 Current Use of Extent GAM Bit Setting SGAM Bit Setting Free, not being used 1 Uniform extent, or full mixed extent Mixed extent with free pages GAMs and SGAMs

Tablespaces and Data files Oracle and SQL Server store data in data files 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 data files

SQL Server Data Files Three file types supported by SQL Server: Primary Data Files Secondary Data Files Log Data Files

Mapping of Tablespaces and Filegroups System Tablespace SysAux Tablespace Temporary Tablespace BigFile Tablespace User Data Tablespace User Index Tablespace Undo Tablespace Redo Log Files Data file Log file Data file Master DB Resource DB TempDB Model DB MSDB User DB Data FG Index FG Log File(s) Data file Log file Data file Tablespace Group Log file Data file Data file Log file Data file Data file Log file Data file Data file Data file User Database Data file Data file Data file Data file Redo Log Log file Oracle Database Instance SQL Server Instance

Demonstration 1: Viewing an Instance’s System Databases In this demonstration you will see how to: Connect to an instance Review system databases Review application or user 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 2: View the Data Dictionary In this demonstration you will learn how to: View the dictionary with object explorer View the data dictionary with catalog views View the data dictionary within a database View the data dictionary via system stored procedures

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