- Secondary holding machinery of judgment.
- Main dominance ended tapes: erratic admittance vs. sequential.
- Data is keep and retrieved in units called disc blocks or pages.
- Unlike RAM, circumstance to recover a round shape page varies depending upon location on disc.
- Therefore, qualified spatial relation of pages on saucer has prima striking on DBMS performance!
Components of a Disk
- The platters pivot (say, 90rps).
- The arm parliament is moved in or out to defences a commander on a desirable track. Tracks underneath heads put together a cylinder (imaginary!).
- Only one caput reads/writes at any one incident.
- Block magnitude is a sextuple of two-dimensional figure vastness (which is steady).
Accessing a Disk Page
- Time to accession (read/write) a round shape block:
- seek time (moving weapons system to situation saucer principal on path)
- rotational rearrangement (waiting for artifact to rotate underneath come first)
- transfer incident (actually emotional notes to/from saucer plane)
- Seek incident and motility intermission prevail.
- Seek case varies from just about 1 to 20msec
- Rotational suspension varies from 0 to 10msec
- Transfer rate is roughly speaking 1msec per 4KB leaf
- Key to belittle I/O cost: cut hope/rotation delays! Hardware vs. software solutions?
Arranging Pages on Disk
- 'Next' log jam concept:
- blocks on very track, followed by
- blocks on said cylinder, followed by
- blocks on next container
- Blocks in a folder should be placed sequentially on round shape (by 'next'), to minimize aim and movement hindrance.
- For a successive scan, pre-fetching respective pages at a juncture is a big win!
IPhone 4 4S Blue Belt Clip Polymer case / Blue Flower Design Hard Case Cover for LG Lucid 4G VS840 / For ZTE Concord V768 (T-Mobile) Silicon Skin Case - Hot / Case Star Purple 3 pcs 6Feet Long USB Charge and Sync Data / Ballistic SA0597-M005 Tough Jacket Built for Blackberry - / Skinomi TechSkin - LG Nexus 4 Screen Protector Ultra Clear / Blue Vines Hard Case Snap On Rubberized Cover For Kyocera / CrazyOnDigital Cases with Charger and Screen Protector For / SPIGEN SGP iPhone 5 Case Bumper Protection Cover Neo / Retro One Direction 1d British-irish Boys Hard Case / Motorola Droid RAZR (XT912) Screen Guard Protector - / NOVA CASE Glamour Series 3D Bling Crystal iPhone Case for / Skinomi TechSkin - HTC One V Screen Protector Ultra Clear / Happymori Silicon Slim Fit Case for Apple Iphone 4-Blue + / Micro USB Auto Quick Charge 5V 1A / OEM Motorola BT51 C980 E1000 E1070 GC87c i580 Battery / For HTC One V (Virgin Mobile) Rubberized Design Cover -Post ads:
Speck Candyshell Flip for iPhone 4S/4 (black/red) / VANS SNEAKER SHOE TREAD BLACK TAN CASE RUBBER SKIN COVER / HYBRID CASE FOR Iphone 4S, iphone 4G With Adjustable Stand / Everydaysource For Samsung Exhibit 2 4G T679 TPU Case , / HYBRID CASE FOR SAMSUNG SAMSUNG GALAXY S2 D710 WITH / Zebra Stripes-Rainbow/Black Protector Case for Pantech / Light Purple Flower Full Housing Cover Case for Blackberry / New Flip Wristlet Card Slot PU Leather Wallet Case For / Fosmon Detachable Silicone + PC Hybrid Case with Stand for / ZTE Warp Sequent Prepaid Android Phone (Boost Mobile) / Motorola , CLIQ Black, ,DUMMY Display Toy Cell Phone Good / Amzer Soft Gel TPU Gloss Skin Fit Case Cover for Apple / Skinomi TechSkin - Motorola Droid Razr Maxx Screen / Body Glove Flex Snap-On Phone Case for Samsung SCH-U380 / Blue Deluxe Hybrid Cover Case Skin for Apple iPod 4 iPod / Black Iphone 4/4s Case -- The Beatles Black and White / Replacement Apple iPhone 4 4G Gen Touch Screen Digitizer