Index Tuning
Conventional index
2017/7/31
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Overview
Duplicate keys
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Duplicate keys
Dense index, one way to implement?
• Query
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– Look for
10
the first K, 20
then
search
forward
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Duplicate keys
Dense index, better way?
• Each pointer
points to the
first of
records with
key K
• Query
– Find the
first
occurrence,
then move
forward
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Duplicate keys
careful if looking
for 20 or 30!
Sparse index, one way?
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• 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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Duplicate keys
Sparse index, another way?
– place first new key from block
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Summary
Duplicate values,
primary index
• Index may point to first instance of
each value only
File
Index
a
a
a
.
.
b
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Deletion from sparse index
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Deletion from sparse index
– delete record 40
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Deletion from sparse index
– delete record 30
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Deletion from sparse index
– delete records 30 & 40
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Deletion from dense index
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Deletion from dense index
– delete record 30
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Insertion, sparse index case
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Insertion, sparse index case
– insert record 34
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34
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• our lucky day!
we have free space
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where we need it!
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Insertion, sparse index case
– insert record 15
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20 15
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• Illustrated: Immediate reorganization
•In principle, we may have had to slide
every record to the end of the file
• Variation:
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– insert new block (chained file)
– update index
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Insertion, sparse index case
– insert record 25
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overflow blocks
(reorganize later...)
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• 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 . . .
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summary