19-physical-notes

19-physical-notes - Physical Data Organization CPS 116...

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1 Physical Data Organization CPS 116 Introduction to Database Systems 2 Announcements (Tue. Nov. 15) ± Homework #3 sample solution available ± Homework #4 will not be officially assigned until next Tuesday ² But you can already start with 4.1 on Gradiance 3 Outline ± It’s all about disks! ² That’s why we always draw databases as ² And why the single most important metric in database processing is (oftentimes) the number of disk I/O’s performed ± Storing data on a disk ² Record layout ² Block layout
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2 4 Storage hierarchy Registers Cache Memory Disk Tapes Why a hierarchy? 5 How far away is data? Location Cycles Registers 1 On-chip cache 2 On-board cache 10 Memory 100 Disk 10 6 Tape 10 9 Location Time (Source: AlphaSort paper, 1995) ) I/O dominates—design your algorithms to reduce I/O! The gap has been widening! 6 A typical disk Spindle rotation Platter Platter Spindle Platter Tracks Arm movement Disk arm Disk head Cylinders “Moving parts” are slow
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3 7 Top view Track Sectors “Zoning”: more sectors/data on outer tracks A block is a logical unit of transfer consisting of one or more sectors 8 Disk access time Sum of: ± Seek time: time for disk heads to move to the correct cylinder ± Rotational delay: time for the desired block to rotate under the disk head ± Transfer time: time to read/write data in the block (= time for disk to rotate over the block) 9
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19-physical-notes - Physical Data Organization CPS 116...

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