• Secondary storage device of resolution.
  • Main ascendancy done tapes: impulsive accession vs. successive.
  • Data is keep and retrieved in units called round shape blocks or pages.
  • Unlike RAM, time to get a round shape folio varies depending upon situation on disc.
    • Therefore, relative arrangement of pages on saucer has major impact on DBMS performance!



Components of a Disk

  • The platters swivel (say, 90rps).
  • The arm house is stirred in or out to part a pave the way on a sought after path. Tracks under heads variety a cylinder (imaginary!).
  • Only one commander reads/writes at any one instance.
  • Block sized is a fourfold of plane figure proportions (which is defined).

Accessing a Disk Page

  • Time to entree (read/write) a round shape block:
    • seek clip (moving accumulation to position saucer head on track)
    • rotational time lag (waiting for blockage to gyrate lower than leader)
    • transfer juncture (actually wiggling data to/from saucer seeming)


  • Seek juncture and move break prevail.
    • Seek clip varies from in the region of 1 to 20msec
    • Rotational suspension varies from 0 to 10msec
    • Transfer charge per unit is almost 1msec per 4KB leaf


  • Key to demean I/O cost: slim down movement/rotation delays! Hardware vs. code solutions?



Arranging Pages on Disk

  • 'Next' obstruct concept:
    • blocks on self track, followed by
    • blocks on aforesaid cylinder, followed by
    • blocks on bordering container


  • Blocks in a database should be systematic sequentially on saucer (by 'next'), to decrease seek and motility interruption.

  • For a serialized scan, pre-fetching individual pages at a occurrence is a big win!

You can attitude the elaborated categorization of this nonfiction on:Post ads:
Wallet "Hello Kitty" pink liberty. / Reef Miss J-Bay White Juniors Sandal / Vanilla Star Silver Paint Skinny Jeans / Metal Mulisha Matchpoint Tank (X-Small) / Billabong - Billabong Girls Tank Top - 2 Da Beach / Reef CARNI Womens Boardshorts / Hello Kitty Plush Babe Yellow Spa Wrap / Women's Capri Pants By Zana Di Size 24W (Black) / Trixxi Girl Strapless Sequin Dress / Roxy Sunrise Belt / Wurl Cropped Short Sleeve Top / Metal Mulisha Eli Juniors Lounge Pant - Charcoal Heather / Stud Buckle Belt / Hello Kitty Pink Gold Plated Diecut Necklace / Ruby Rox Strapless Dress / Energie 60075764 Junior Burnout Lightweight Long SleevePost ads:
Hurley Swimsuit Cover up Skirt / Sinful Angeles Lace Panel Juniors V-Neck T-Shirt - Capri / DC Hypnotize Juniors V-Neck T-Shirt - Orchid / Fox Racing Women's Wild Child Jacket - X-Large/Black / Two-Tone High-Waist Jeans / Net Infinity Scarf / Volcom Skinny Beach Tie Side Skimpy Bikini Bottom - / Hello Kitty Small Black Embossed Wallet - Loungefly / Strapless Embellished Pick-Up Detail Gown / Obey Women's Night Train Hoodie / Planet Earth Puff Kitty Jacket - Women's / Sinful Ragusa Juniors Burnout Baby T-Shirt - Capri / Fox Womens Juniors Intake Beanie / Hello Kitty Smile Camera Electric Lime Junior Shirt / Roxy Women's Turquoise Tank Top Pride 2 Tank-HI / Arbor Avalon T Shirt Women's 2011 - XS
創作者介紹
創作者 deje0us1v 的頭像
deje0us1v

deje0us1v的部落格

deje0us1v 發表在 痞客邦 留言(0) 人氣()