1. CS 4432 Database Systems II Lecture 1: Introduction
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2. A Brief Pre-amble
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3. Implementing a Database System? Simple?
Relations
Statements
Results
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4. Naïve Implementation Relations stored in files (ASCII)
e.g., relation Students is in /usr/db/Students
Students
Depts
Smith # 123 # CS
Jones # 522 # EE
CS # Fuller Labs
EE # Atwater Kent
PH # Olin Hall . .
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5. Naïve Implementation Details
Directory file (ASCII) in /usr/db/schema
Students#name#STR#id#INT#dept#STR
Depts#name#STR#office#STR . . .
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6. Sample Query select Students.name,Depts.office from Students,Depts
where Students.dept = Depts.name and Students.id > 300 #
Smith # 123 # CS # CS # Fuller Labs
Smith # 123 # CS # EE # Atwater Kent
Smith # 123 # CS # PH # Olin Hall
Jones # 522 # EE # CS # Fuller Labs
Jones # 522 # EE # EE # Atwater Kent
Jones # 522 # EE # PH # Olin Hall
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7. Execution Process To execute “select * from R where condition”:
(1) Read dictionary to get R attributes
(2) Read R file, for each line:
(a) Check condition
(b) If OK, display
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8. Yet Another Execution
To execute “select A,B from R,S where condition”:
(1) Read dictionary to get Students,Depts attributes
(2) Read Students file, for each line:
(a) Read Depts file, for each line:
(i) Create join tuple
(ii) Check condition
(iii) Display if OK
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9. What’s wrong ? Layout ? Tuple layout on disk Example:
- Change string from ‘Cat’ to ‘Cats’ and we have to rewrite file
- ASCII storage is expensive
- Deletions are expensive
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10. What’s wrong ? Search ? Search expensive; no indexes
e.g., - Cannot find tuple with given key quickly
- Always have to read full relation
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11. What’s wrong ? Brute force query processing e.g., select * from R,S
where R.A = S.A and S.B > 1000
- Do select first?
- More efficient join?
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12. What else is wrong ? Missing ?
No buffer manager :
Need caching
No concurrency control:
Multiple users access and modify same data ?
No reliability:
lose data? leave operations half done ?
No security:
-File system insecure? Too coarse security?
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13. System Structure Strategy Selector Query Parser User User Transaction
Transaction Manager
Concurrency Control
Buffer Manager
Recovery Manager
Lock Table
File Manager
M.M. Buffer
Log
Statistical Data
Indexes
User Data
System Data
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14. Course Overview File & System Structure
Records in blocks, dictionary, buffer management,…
Indexing & Hashing
B-Trees, hashing,…
Query Processing
Query costs, join strategies,…
Crash Recovery
Failures, stable storage,…
Concurrency Control
Correctness, locks,…
Transaction Processing
Logs, deadlocks,…
Additional Topics
If time permits …
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15. Next time: The lowest layer : Brief look at hardware
Start to look at chapter 13
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