11.1Database System Concepts. 11.2Database System Concepts Now Something Different 1st part of the...
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Transcript of 11.1Database System Concepts. 11.2Database System Concepts Now Something Different 1st part of the...
11.1Database System Concepts
11.2Database System Concepts
Now Something DifferentNow Something Different
1st part of the course: Application Oriented
2nd part of the course: Systems Oriented
What is “Systems”?
A: Not Programming Not programming big things..
Systems = Efficient and safe use of limited resources (e.g., disks)
Efficient: resources should be shared, utilized as much as possible
Safe: sharing should not corrupt work of individual jobs
11.3Database System Concepts
General OverviewGeneral Overview
Relational model - SQL Formal & commercial query languages
Functional Dependencies Normalization
Physical Design Indexing Query evaluation Query optimization ….
ApplicationOriented
Systems Oriented
11.4Database System Concepts
The systems side of DatabasesThe systems side of Databases
What will we talk about?
1. Data Organization: physical storage strategies to support efficient updates, retrieval
2. Data retrieval: auxiliary data structures to enable efficient retrieval. Techniques for processing queries to ensure efficient retrieval
3. Data Integrity: techniques for implementing Xactions, to ensure safe concurrent access to data. Ensuring data is safe in the presence of system crashes.
11.5Database System Concepts
Data OrganizationData Organization
Key points
1. Storage Media “Memory hierarchy” Efficient/reliable transfer of data between disks and main memory Hardware techniques (RAID disks)
Software techniques (Buffer mgmt)
2. Storage strategies for relations-file organization Representation of tuples on disks
Storage of tuples in pages, clustering.
11.6Database System Concepts
CPU
M C
TypicalComputer
SecondaryStorage
......
11.7Database System Concepts
Storage Media: PlayersStorage Media: Players
Cache – fastest and most costly form of storage; volatile; managed by the computer system hardware.
Main memory: fast access (10s to 100s of nanoseconds; 1 nanosecond = 10–9 seconds)
generally too small (or too expensive) to store the entire database
Volatile — contents of main memory are usually lost if a power failure or system crash occurs.
But… CPU operates only on data in main memory
11.8Database System Concepts
Storage Media: PlayersStorage Media: Players
Disk Primary medium for the long-term storage of data; typically stores entire database.
random-access – possible to read data on disk in any order, unlike magnetic tape
Non-volatile: data survive a power failure or a system crash, disk failure less likely than them
New technology: Solid State Disks and Flash disks
11.9Database System Concepts
Storage Media: PlayersStorage Media: Players Optical storage
non-volatile, data is read optically from a spinning disk using a laser
CD-ROM (640 MB) and DVD (4.7 to 17 GB) most popular forms
Write-one, read-many (WORM) optical disks used for archival storage (CD-R and DVD-R)
Multiple write versions also available (CD-RW, DVD-RW, and DVD-RAM)
Reads and writes are slower than with magnetic disk
Tapes Sequential access (very slow) Cheap, high capacity
11.10Database System Concepts
Memory HierarchyMemory Hierarchycache
Main memory
disk
Optical storage
Tapes
Higher speed
Lower price
Traveling the hierarchy:1. speed ( higher=faster)2. cost (lower=cheaper)3. volatility (between MM and Disk)4. Data transfer (Main memory the “hub”)5. Storage classes (P=primary, S=secondary,T=tertiary)
V
NV
11.11Database System Concepts
Main memory Main memory Disk Data Xfers Disk Data Xfers
Concerns:1. Efficiency (speed)
can be improved by...
a. improving raw data transfer speed
b. avoiding untimely data transfer
c. avoiding unnecessary data transfer
2. Safety (reliability, availability)
can be improved by...
a. storing data redundantly
11.12Database System Concepts
Hard Disk MechanismHard Disk Mechanism
11.13Database System Concepts
Read-write head Positioned very close to the
platter surface (almost touching it)
Surface of platter divided into circular tracks
Each track is divided into sectors. A sector is the smallest unit
of data that can be read or written.
To read/write a sector disk arm swings to position
head on right track platter spins continually;
data is read/written as sector passes under head
Block: a sequence of sectors Cylinder i consists of ith
track of all the platters
11.14Database System Concepts
“Typical” ValuesDiameter: 1 inch 15 inchesCylinders: 100 2000Surfaces: 1 or 2(Tracks/cyl) 2 (floppies) 30Sector Size: 512B 50KCapacity: 360 KB (old floppy)
1.5 TB
11.15Database System Concepts
Performance Measures of DisksPerformance Measures of DisksMeasuring Disk Speed
Access time – consists of: Seek time – time it takes to reposition the arm over
the correct track.
(Rotational) latency time – time it takes for the sector to be accessed to appear under the head.
Data-transfer rate – the rate at which data can be retrieved from or stored to the disk.
Analogy to taking a bus:
1. Seek time: time to get to bus stop
2. Latency time; time spent waiting at bus stop
3. Data transfer time: time spent riding the bus