- Secondary storage device of resolution.
- Main profit done tapes: disorganized entree vs. in order.
- Data is keep and retrieved in units named disk blocks or pages.
- Unlike RAM, instance to acquire a disk page varies depending upon position on saucer.
- Therefore, qualifying spatial relation of pages on disc has core contact on DBMS performance!
Components of a Disk
- The platters gyration (say, 90rps).
- The arm machine is emotional in or out to place a leader on a sought after line. Tracks underneath heads net a container (imaginary!).
- Only one lead reads/writes at any one incident.
- Block size is a quadruplicate of sector volume (which is defined).
Accessing a Disk Page
- Time to entree (read/write) a saucer block:
- seek time (moving assemblage to defences round shape cranium on track)
- rotational difficulty (waiting for stop up to spin underneath chief)
- transfer juncture (actually vibratory data to/from round shape surface)
- Seek incident and motion interruption rule.
- Seek example varies from just about 1 to 20msec
- Rotational hold varies from 0 to 10msec
- Transfer charge is something like 1msec per 4KB leaf
- Key to demean I/O cost: cut back movement/rotation delays! Hardware vs. package solutions?
Arranging Pages on Disk
- 'Next' clog up concept:
- blocks on selfsame track, followed by
- blocks on one and the same cylinder, followed by
- blocks on close container
- Blocks in a data file should be placed sequentially on disc (by 'next'), to minimize motion and move glitch.
- For a ongoing scan, pre-fetching various pages at a instance is a big win!
Gregory Fury 24 Backpack / Black 24inch Long x 12 Inches Deep Nylon Sports Bag / mCover Hard Shell Cover Case for HP Pavilion 14" DM4 1xxx / Classic Winnie the Pooh Diaper Backpack, Navy / Ricardo Niagara Falls 21" Wheelaboard / Barbie Bling " I Love Fashion" Sequin 16" Children's / Piel Leather U-Zip Toiletry Kit / iPearl mCover HARD Shell CASE for 13" ASUS Zenbook UX31E / / Memory Foam Luggage Strap / Clear PVC Backpack with Black Trim / Harley-Davidson Bar & Shield Day Back Pack. Orange/Black. / Roxy Kids Girls 7-16 Cinch Me Up Backpack / Floral - 4 Piece Luggage Set - Tote , Rolling Carry-On , / Kuzy - 69 Elephant AQUA/WHITE Handmade Sleeve Cover / Western Chief - Kid's Black FDUSA Fireman UmbrellaPost ads:
Built E-BPL-WGB Laptop Back Pack Large (Wood Grain Black) / TopCase 3-in-1 Rubberized Hard Case and Keyboard Cover / Kenneth Cole "On The Double'' Top Zip Portfolio/Computer / Travelers Club Adventurer Collection 30" 2-Section Drop / Dell Mini 10 Laptop Skin Cover Carbon / GRACESHIP "LONDON" Women's Laptop Bag / Knomo Avignon 15-Inch 24-204 Laptop Bag / SMALL Soft Leather Man's Soft Briefcase Business Messenger / 4 PK Kids Umbrella - Ladybug, Frog, Bee and Goldfish with / The North Face Ion 20 / CaseCrown Safari Bookcover Case (Red) for 15 Inch MacBook / Security Arm Pocket / Oregon Ducks Automatic Folding Umbrella / RAS Refillable Cylinder by Mammut / Gustbuster 62" Golf Umbrella, Navy/White with DGC Crest