Extensions to Multi Query Optimization

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Extensions to Multi Query Optimization

• Amit Gupta
• IIT Bombay

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Recap of MQO

• AND-OR DAG of the set of Queries
• Transformation
• Greedy Algorithm
• Choose highest benefit shared node to be cached

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MQO for Fixed Cache Size

• Greedy heuristic
• Choose shared node with highest benefit/Size to
  be cached
• Disadvantage of Greedy
• less search space

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Problem Definition

• Given set of shared nodes S ( s?, s?,..) and
  cache size C.
• Choose subset P from S, such that
• ? size(p) lt C , where p ? P
• benefit of caching P is maximized.

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Subset sum Problem

• Given set S ( s?, s?,..) and C,
• choose the subset P from S such that
• ? p lt C , where p ? P and
• ? p is maximized.

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Subset sum Algorithm

• Given set S ( s?, s?,..)
• Exponential Algorithm
• Search Space Power set of S.
• Approximation Algo
• Given ? as error constant
• Search Space Trimmed Power Set of S.
• Approximation Ratio ?

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MQO for fixed Size Cache

• Given
• S set of shared nodes
• C Cache Size
• Error constant ?
• Search Space of trimmed Power set of S.
• Trimming procedure

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MQO cont.

• Advantage of Subset sum Algorithm
• More Search space
• ? can be changed

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Scheduling in MQO
nodes to be cached
Plan DAG