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Index Tuning

Conventional index

Overview

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Duplicate keys

1010

2010

3020

3030

4540

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1010

2010

3020

3030

4540

10101020

20303030

1010

2010

3020

3030

4540

10101020

20303030

Dense index, one way to implement?

• Query– Look for

the first K, then search forward

Duplicate keys

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1010

2010

3020

3030

4540

10203040

Dense index, better way?

Duplicate keys

• Each pointer points to the first of records with key K

• Query– Find the

first occurrence, then move forward

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1010

2010

3020

3030

4540

10102030

Sparse index, one way?

Duplicate keysca

refu

l if lookin

gfo

r 2

0 o

r 3

0!

• Find the last index entry with key <=K

• Then, search backward until coming to the first entry or meeting an index entry E2

with key strictly less than k

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1010

2010

3020

3030

4540

10203030

Sparse index, another way?

Duplicate keys

– place first new key from block

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Duplicate values, primary index

• Index may point to first instance ofeach value only

File

Index

Summary

aaa

b

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Deletion from sparse index

2010

4030

6050

8070

10305070

90110130150

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Deletion from sparse index

2010

4030

6050

8070

10305070

90110130150

– delete record 40

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Deletion from sparse index

2010

4030

6050

8070

10305070

90110130150

– delete record 30

4040

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Deletion from sparse index

2010

4030

6050

8070

10305070

90110130150

– delete records 30 & 40

5070

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Deletion from dense index

2010

4030

6050

8070

10203040

50607080

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Deletion from dense index

2010

4030

6050

8070

10203040

50607080

– delete record 30

4040

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Insertion, sparse index case

2010

30

5040

60

10304060

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Insertion, sparse index case

2010

30

5040

60

10304060

– insert record 34

34

• our lucky day! we have free space where we need it!

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Insertion, sparse index case

2010

30

5040

60

10304060

– insert record 15

15

2030

20

• Illustrated: Immediate reorganization

•In principle, we may have had to slide every record to the end of the file

• Variation:– insert new block (chained file)– update index

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Insertion, sparse index case

2010

30

5040

60

10304060

– insert record 25

25

overflow blocks(reorganize later...)

• No index entry for overflow blocks, which is considered as an extension of data block

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Insertion, dense index case

• Similar

• Often more expensive . . .

summary