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Database Chapter Processing 4 Chapter 4 Physical Database Layouts Chapter 4 Main Points • Database File Layout • Verification of I/O Weighting Estimates • File Location • Database Space Usage Overview Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Database File Layouts • Establish clear goals of the file distribution design • Understand the nature of the database – Transaction-oriented vs Read-Intensive Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Database File Layout (6 steps) 1. Identify I/O contention among datafiles – – – – Use statistics from analogous database if available Assign I/O weights based on estimates relative to most active tablespace See Table 4-1 for datafiles in optimal database See Table 4-2 for estimated I/O weights for sample tablespaces Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Table 4-1 TABLESPACE SYSTEM DATA DATA_2 INDEXES INDEXES_2 RBS RBS_2 TEMP TEMP_USER TOOLS TOOLS_1 USERS MEANING Data Dictionary Standard-operation tables Static tables used during standard operation Indexes for Standard-operation tables Indexes for the static tables Standard-operation rollback segments Specialty rollback segments used for data loads Standard operation temporary segments Temporary segments created by a particular user RDBMS tools table Indexes for RDBMS tools table User objects, in development database Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Table 4-2 PERCENT OF TOTAL TABLESPACE WEIGHT DATA RBS SYSTEM INDEXES TEMP DATA_2 INDEXES_2 TOOLS Copyright © 2001 Harold Pardue, University of South Alabama 100 40 35 33 5 4 2 1 220 46% 18% 16% 15% 2% 2% 1% 1% 100% Chapter 4 - Physical Database Layouts Chapter 4 Database File Layout 2. Identify I/O bottlenecks among all database files – – – – – Location of datafiles relative to each other Online redo log files should not be stored on same disk as any other active datafile Control file requires little I/O LGWR-ARCH contention-don’t store Archive redo log files on same disk as redo log files Oracle software—no statistics kept on I/O Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Background Processes 3. Types – Concurrent I/O—multiple accesses performed against same device at same instant – Interference—writes to a sequentially written file are interrupted by reads or writes to other files on the same disk • DBWR—reads and writes in random manner – Can be in contention with itself – ORACLE supports multiple DBWR processes for each instance • LGWR—writes sequentially to one file at a time • ARCH—reads and writes sequentially to one file at a time Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Security and Performance Goals 4. Recoverability—takes into account all processes that impact disk – Must mirror online redo log files (OS or redo log groups) – Prevails over performance tuning • Performance tuning goals—take into account the projected database file I/O distribution and the relative access speeds of the disk Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 System Hardware and Mirroring Architecture 5. Number of disks required • Determined byDatabase size and database I/O weights – Models of disks required – Appropriate mirroring strategy Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Dedicated Database Disks 6. Identify Disks that can be dedicated to the database • To avoid concurrent I/O and interference with Non-ORACLE files Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Verifying I/O Weighting Estimates • Statistics table – Found in data dictionary – Compare to initial estimates and adjust – See page 100 for sample use of the view V$FILESTAT Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Summary: Basis for disk layout • • • • • • • • • Recovery Mirroring of online redo log files Database file I/O weight estimation Contention among background processes Contention between disks for DBWR Defined performance goals Known disk hardware options Known disk mirroring architecture Dedicated database disks Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Decisions • The author provides guidance physical disk layout decisions – “Dream” physical disk layout is best case scenario – Each successive iteration suggests the best compromise at that point – Similar to guidance for “Denormalizing” a database that has been fully normalized. – Will illustrate one iteration…see author for iterations 2-6! Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Dream Physical Layout—22 Disks • Disk 1 2 3 4 5 6 7 8 9 10 11 Contents Oracle Software System Tablespace RBS Tablespace DATA Tablespace INDEXES Tablespace TEMP Tablespace TOOLS Tablespace Online Redo log 1 Online Redo log 2 Online Redo log 3 Control File 1 Copyright © 2001 Harold Pardue, University of South Alabama • Disk 12 13 14 15 16 17 18 19 20 21 22 Contents Control File 2 Control File 3 Application Software RBS_2 DATA_2 INDEXES_2 TEMP_USER TOOL_I USERS Archived redo log disk Export dump file disk Chapter 4 - Physical Database Layouts Chapter 4 First Iteration—17 Disks • Disk 1 2 3 4 5 6 7 8 9 1. Contents Oracle Software System Tablespace RBS Tablespace DATA Tablespace INDEXES Tablespace TEMP Tablespace TOOLS Tablespace Online Redo log 1 Control File 1 Online Redo log 2 Control File 2 • Disk 10 Contents Online Redo log 3 Control File 3 11 Application Software 12 RBS_2 13 DATA_2 14 INDEXES_2 15 TEMP_USER 16 Archived redo log disk 17 Export dump file disk TOOL_I and USERS are omitted Control Files have least interference with Online Redo log files 2. See author notes for rationale re TOOL_I and USER omission Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 File Location • Database files – Separated from other software – Stored in directories created specifically for that database – Of different database should not be stored together Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Database Space Usage Overview • Storage Clause—default parameters – – – – – – Initial extent size Next extent size Pct increase (careful use and monitoring) Max extents Min extents Pct Free clause Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Sizing • Pertains to – – – – – Table segments Index segments Rollback segments Temporary segments Free space Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts Chapter 4 Scenarios • Remainder of Chapter 4 is how-to-do to achieve specific goals – – – – – – Resizing Datafiles (7.2 and higher) Automating Datafile Extensions Moving Database Files Moving Online Redo Log Files Moving Control Files Deallocating Space in 7.2 and 7.3 • Shrinking Datafiles • Shrinking Tables, Clusters and Indexes • Rebuilding Indexes Copyright © 2001 Harold Pardue, University of South Alabama Chapter 4 - Physical Database Layouts