Module 2: Database Architecture

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) Table Oracle Table SQL Server Index View Synonym Sequence Procedure Function Package Queue in Streams Advanced Queuing Object Type XML DB Index View Synonym Sequence Stored Procedure Function N/A Service Broker Queue Type 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 s 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 s; 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 6 x = 1 EXTENT 1 + 16K = 2 SEGMENT (Table/Index) 8 x = 64K EXTENT 64K + 64K = 12 HEAP/INDEX 8 x = 16K EXTENT 8 x = 64K EXTENT Oracle 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 s 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 GAMs and SGAMs Current Use of Extent 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

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

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 (s, 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