Notes02 - Outline CS 245 Database System Principles Notes...

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1 CS 245 Notes 2 1 CS 245: Database System Principles Notes 02: Hardware Hector Garcia-Molina CS 245 Notes 2 2 Outline • Hardware: Disks • Access Times • Example - Megatron 747 • Optimizations •Other Top ics: –S t o r a g e c o s t s – Using secondary storage –D i s k f a i l u r e s CS 245 Notes 2 3 Hardware DBMS Data Storage CS 245 Notes 2 4 P M C Typical Computer Secondary Storage ... ... CS 245 Notes 2 5 Processor Fast, slow, reduced instruction set, with cache, pipelined… Speed: 100 500 1000 MIPS Memory Fast, slow, non-volatile, read-only,… Access time: 10 -6 10 -9 sec. 1 s 1 ns CS 245 Notes 2 6 Secondary storage Many flavors: - Disk: Floppy (hard, soft) Removable Packs Winchester Ram disks Optical, CD-ROM… Arrays - Tape Reel, cartridge Robots
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2 CS 245 Notes 2 7 Focus on: “Typical Disk” Terms: Platter, Head, Actuator Cylinder, Track Sector (physical), Block (logical), Gap CS 245 Notes 2 8 Top View CS 245 Notes 2 9 “Typical” Numbers Diameter: 1 inch 15 inches Cylinders: 100 2000 Surfaces: 1 (CDs) (Tracks/cyl) 2 (floppies) 30 Sector Size: 512B 50K Capacity: 360 KB (old floppy) 400 GB (I use) CS 245 Notes 2 10 Disk Access Time block x in memory ? I want block X CS 245 Notes 2 11 Time = Seek Time + Rotational Delay + Transfer Time + Other CS 245 Notes 2 12 Seek Time 3 or 5x x 1N Cylinders Traveled Time
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3 CS 245 Notes 2 13 Average Random Seek Time  SEEKTIME (i j) S = N(N-1) NN i=1 j=1 j i CS 245 Notes 2 14 Average Random Seek Time SEEKTIME (i j) S = N(N-1) i=1 j=1 j i “Typical” S: 10 ms 40 ms CS 245 Notes 2 15 Rotational Delay Head Here Block I Want CS 245 Notes 2 16 Average Rotational Delay R = 1/2 revolution “typical” R = 8.33 ms (3600 RPM) CS 245 Notes 2 17 Transfer Rate: t • “typical” t: 1 3 MB/second • transfer time: block size t CS 245 Notes 2 18 Other Delays • CPU time to issue I/O • Contention for controller • Contention for bus, memory
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4 CS 245 Notes 2 19 Other Delays • CPU time to issue I/O • Contention for controller • Contention for bus, memory “Typical” Value: 0 CS 245 Notes 2 20 • So far: Random Block Access • What about: Reading “Next” block?
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Notes02 - Outline CS 245 Database System Principles Notes...

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