1. Data Storage ManagementV
Data Storage Management
Yunsheng Liu
Software College, HUST

2. 5.1 The Memory Hierarchy 5.1.1 The Storage Levels
CPU
Cache
Main Memory
Magnetic Disk
Magnetic Tape
Request for data
Data satisfying request
Tertiary storage
Secondary storage
Primary storage
Fresh Memory
Optical Disk
EEPROM
CD-ROM
Yunsheng Liu

3. 5.1.2 Disk Property— electrical erasable
Tracks
Block
Cylinder
Platter
Sector
Gaps
Disk head
Disk arm
Spindle
Yunsheng Liu

4. 5.1.2 Disk Property
2. Performance property of disks 1). Data must be in main memory for the DBMS to operate on it 2). The unit for data transfer between main memory and disk is a block.  R/W a disk block is called an I/O 3). Block access time—from when an R/W is issued to when the block appears in MM:
access time=seek time+rotational delay+transfer time
Yunsheng Liu

5. 5.1.2 Disk Property 3. Performance measures of disks Capacity
Access latency( seek time + rotational latency time)
Data transfer rate
3. Performance measures of disks
4. Optimization of disk-block access
File organization
Scheduling (Disk-arm, i.e. I/O)
Nonvolatile RAM for writing: Battery-backed-up RAM
Log disk—devoted to writing log in much the same
way as non-V RAM. Log-based file system
Yunsheng Liu

6. 5.1.3 RAID Concept RAID—Redundant Arrays of Independent(historically
Inexpensive) Disks
A Disk array—an arrangement of several disks,
organized so as to
Increase performance—data striping
Improve reliability—redundancy
RAID Levels
Level 0: Nonredundant striping
Level 1: Mirrored disks
Level 2: Error-correcting code (ECC)
Yunsheng Liu

7. 5.2 Stored Data Management
5.2.1 Introduction
1. Stored Data Kinds:
 User database
 Data Dictionary/ Directory,
 Log
2. Stored Data Structures:
 Arrangement: sequential, random
 Connection: address adjacent, chaining
3. Access modes: sequential, indexed, hashing
4. I/O Buffer management
5. Interface to OS
Yunsheng Liu

8. 5.2.2 Storage Management Structures
5.2 Stored Data Management
5.2.2 Storage Management Structures
Logical structure:
 Logical file page record field
2. Physical structure
 Stored structure: stored file stored record 
stored item
 Device structure: device  volume cylinder track physical record/sector
3. Allocation structure
 Extent block
Yunsheng Liu

9. 5.2 Stored Data Management
4. Mapping From Logical Structure to Physical Structure
Volume
Sector
Logical structure
Stored structure
Allocation structure
Physical structure
Logic File
Page
Logic Record
Field
Stored File
Stored Record
Stored Item
Cylinder
Track
Block
Extent
Yunsheng Liu

10. 5.2 Stored Data Management
5.2.3 Overview of File Organizations 1. Stored Data Arrangement 2. Access Modes
File Org.
Sequential File
Random File
Heap File
Sorted File
Indexed File
General Index File
Hash File
Tree Index File
B+-Tree
B-Tree
Static Hash
Dynamic Hash
Yunsheng Liu

11. 5.2 Stored Data Management
3. Classification of File Organizations
Adjacent
Chained
Sequential
Indexed
sequential
Tree-
structural
Static
hash
Dynamic
Sequential processing
Random processing
Storage
structure
Heap
Sorted
Hashed
Access
mode
Chain
Yunsheng Liu

12. 5.3 Sequential File Structure
- How to organize blocks/pages in a file to support to
create, destroy a file, and get, insert, delete a record
and scan all records in the file
Conjunctive arrangement of blocks
File Head
Free blocks
Data block 1
Data block 2
Data block N
Frame 1
Frame 2
Frame N
Frame N+m
• • •
Fid P
Problems: how to insert, delete?
how many free slots/pages?
Yunsheng Liu

13. 5.3 Sequential File Structure
Example
Student
S# SName SAge Dept
李红光 SW
何清溪 MS
刘要武 CS
李 光 EE
刘 民 CS
张一清 MS
张扬名 SW
王克勤 EE
(a). Natural Sequence Structure
Student
S# SName SAge Dept
李 光 EE 李红光 SW
王克勤 EE
刘 民 CS
刘要武 CS
张一清 MS
张扬名 SW
何清溪 MS
(b). Ordered Sequence Structure
Yunsheng Liu

14. 5.4 Chained List File Structure
Data page
Fid P 
File Header
(a). Hybrid Chain …
Data block 
(b) Separated Chain
File Header P1 P2
Fid …
The space for pointers of the chains
Virtually, the full list will be empty in variable record
Yunsheng Liu

15. 5.5 Index Structures 5.5.1 Overview of Indexes 1. Concepts
An index is an auxiliary data structure that is intended
to help us find Rids of records with given search key
value
An index is a file/collection of records, referred as
index entries, which are usually pairs (k, Rid) and
Rid is a pointer to a record with search key value k
An index is a mechanism of KTA(Key to Address)
Yunsheng Liu

16. 5.5.1 Overview of Indexes 2. Generic index structure k Indexing on SK
Index entries
Search key
The records with the value k of SK
ridi ki
ridr kr
ridj kj
Index
   SK
Data File
Domain of
Yunsheng Liu

17. 5.5.1 Overview of Indexes 3. Index file organizations
How to organize index entries to support rapid retrieval of entries with a given search key value? e.g.
Sequential indexes
Various tree-structural indexes,
Hash-based indexes—Scatter Table
Yunsheng Liu

18. 5.5.2 Properties of Indexes Clustered vs. Unclustered
 Clustered — the ordering of data records is the same
as (or close to ) the ordering of index entries
- The two orderings are matched with each other
 Unclusterd — not match with each other
Dense vs. Sparse
 Dense: an index entryindividual data record
 Sparse: an index entrya set (usually, a block/page)
of data records
Yunsheng Liu

19. 5.5.2 Properties of Indexes Primary vs. Secondary
 Primary index  Primary key
 Secondary index  Candidate/Secondary key
Simple vs. Composite Key
 Composite key more than one fields
 Simple key  single field
Yunsheng Liu

20. 5.6 B-Tree Structured Indices
Nonleaf Node structure
- - … Pn
Pn-1
• • •
Kn rn P2
K2 r2 P1
K1 r1 P0
Root Node
Inner Nodes
R(K1)
R(K2)
Data Records
Yunsheng Liu

21. … 5.6 B-Tree Structured Indices Leaf Node Structure A B-tree structurerm Km … r2 K2 r1 K1
R(K1)
R(K2) …
A B-tree structure - 10 20  60 70 50 … 3 5
 - 52 54 55
 - 74 78 61 63 65 69
 11 13 14
 - 22 23
R(50)
R(20)
R(10)
R(60)
R(70)
Yunsheng Liu

22. 5.7 B+-Tree Structured Indices
Nonleaf Node structure Pn
Pn-1
• • • Kn P1 K1 P0 P2 K2
Leaf Node Structure rm Km … r2 K2 r1 K1
Yunsheng Liu

23. 5.7 B+-Tree Structured Indices
A B+-tree structure
Random access
Index Set
Sequence Set
Record Set
B+-tree
Data File
Sequential access  
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24. 5.8 Hashing File Structures
General Hashing Structure B0 B1
Bn-1
• • •
h(ki) ki
Hash Function
Major Data Area
Overflow Area
Record slot
Block
Yunsheng Liu

25. 5.8 Hashing File Structures
Bucket Hashing
Primary blocks
Hashing
Function
Key
KTA Transformation
Buckets
Bu1
Bu2
Bun
• • •
Yunsheng Liu