Transcript
DBMS, JVP Magnetic Tapes
Optical Disk
Magnetic Disk
Flash Memory
Main Memory
Cache
Storage Device Hierarchy
Cost
Access Speed
DBMS, JVP
• Fastest• Most Costly Media• Small & is managed by System H/W• Generally is inbuilt on-chip memory• For storage of important & critical
instructions• If size of cache is increased –
- cost increased- benefits of cache is lost
DBMS, JVP
• Machine instructions are stored in main memory
• Its is quite small for storing Database
• Its Volatile i.e. data is lost on power failure or system crash
DBMS, JVP
• EEPROM
• Read is Faster
• Write is very slow & complicated
• 4-10 microsec to write, can’t be overwritten
• To overwrite, has to erase entire data of memory
• Used generally for hand-held & digital electronics devices
DBMS, JVP
• Stores the Database, data moves between Main Memory & Disk
• Size – Few GB upto 80GB
• Size of Magnetic Disk needs increases as we have requirement for larger capacity disks
• Can survive power failure & system crash, is non-volatile storage media
• Disk Failure results in loss of data stored on disk.
DBMS, JVP
• CD – holds about 640MB • DVD – holds 4.7 or 8.5GB per side to 17GB for
two-sided disk
• Data is stored optically on a disk, is read by laser• WORM-write once read many CDs & DVDs• CD-RW & DVD-RW : For multiple writes & read
• CDs are magnetic-optical storage devices that use optical means to read magnetically encoded data.
• Used for archival storages
DBMS, JVP
• Used for Backup Storage
• Cheaper & Slower Access
• Sequential-access Storage
• Not direct access like CDs
• Used for holding large backup data of large organization
DBMS, JVP
Track i
Platter
Cylinder i
Spindle
R-W Head
Disk Arm
Arm Assembly
DBMS, JVP
• Access Time :
Read Req. Issued – Actual Data Transfer Begin• Seek Time : Avg. Seek Time
Time For Repositioning the arm• Rotational Latency Time : Avg. RLT
Time waiting for sector to appear under head• A T = S T + RL T• Data Transfer Rate : rate of data read/write to disk• Mean Time To Failure (MTTF)
Amount of time on avg. we expect system to work w/o failure, measure of reliability of disk
DBMS, JVP
• Reliability of Disk : 1,00,000/100 = 1000 hours
• Disk Failure leads to loss of data
• So keep redundancy i.e. Mirroring of Disk
• MTTF of mirrored disk depends on MTTR, time to replace failed disk & restore data
• First write to one copy them to other so on power failure, blocks have complete data.
DBMS, JVP
• Parallel access to disks• Improve the transfer rate by ‘Striping’• Bit-level striping : splitting bits of each byte
across multiple disks, array of 4,8,16… disks, increase R/W at 8 times
• Block-level striping : divide data into blocks, each block in a disk.
• ith block is in (i mod n + 1)th disk, n=total no. of disks in array.
• Balances load across multiple disks so access is fast & o/p is high
DBMS, JVP
CCCC
DBMS, JVP
PP P
DBMS, JVP
P
P P P P
P
DBMS, JVP
PP P
PP
P
DBMS, JVP
• Monetary Cost of extra disk
• Performance – no. of I/O Operations
• Performance when Disk fails
• Performance to rebuild the Data
RAID 0, 1, 5 are currently in use
DBMS, JVP
• File is organized logically as a sequence of records. The records are stored in disk blocks.
Fixed Length RecordsVariable Length Records
DBMS, JVP
• Deposit = record
acc_no:char(10);
br_nm:char(22);
bal:real;
end
Total = 40 bytes
Acc_no
Br_nm Bal
A-104 Bombay 500
A-121 Delhi 781
A-393 Pune 900
A-129 Bombay 400
A-214 Chennai 164
R-1
R-2
R-3
R-4
R-5
DBMS, JVP
A-104 Bombay 500
A-121 Delhi 781
A-393 Pune 900
A-129 Bombay 400
A-214 Chennai 164
Header
DBMS, JVP
• Records has varying length
• Account_list : record
Br_nm:char(22);
accounts :- array(1---infinite)
acc_no:char(10);
bal:real;
end
end
DBMS, JVP
• Dis. Adv. –
- Not easy to occupy space left by deleted record
Leads to small fragments on disk
- No space for records to grow
Header has info :
- No. of records
- Free space pointer
- Size of each record block
DBMS, JVP
• Reserved Space
• List Representation– Anchor Block– Over Flow Block
DBMS, JVP
• Heap file organization
• Sequential file organization– Search Key– Insert & Deleted using Overflow Block
• Hashing file organization
• Clustering file organization
DBMS, JVP
• A database that maintains data about relations, stores information about the tables of the database.
• E.g. Name of relations
Names of Attributes
Domains & Length
Constraints
DBMS, JVP
DBMS, JVP
• Ordered Indices
• Hash Indices
Aspects :-
- Access Type : by value or range
- Access Time
- Insertion Time
- Deletion Time
- Space Overhead
DBMS, JVP
• Primary Index– Dense Index– Sparse Index
Multilevel Indices
Secondary Indices
DBMS, JVP
• Hash File Organization
- Hash Function
- Uniform Distribution
- Random Distribution
- Bucket
Bucket Overflow & Skew
Overflow Chining
• Hash Indices
• Comparison of Indexing & Hashing
DBMS, JVP
top related