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QuerySplit and Cardinality Estimation Errors

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QuerySplit and Cardinality Estimation Errors

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Questions and Answers

What is the lesson learned for future improvements in query optimization?

Mediocre optimizers are suitable for handling heavy subqueries

Heavy subqueries should be executed first for better performance

Using alternative re-optimization algorithms is the best approach

Fine-grained subqueries are preferred for re-optimization to avoid cardinality estimation errors (correct)

What percentage of the queries belong to the first two categories where QuerySplit outperforms alternative re-optimization algorithms?

40%

70% (correct)

50%

30%

What is a significant finding about the 'Worse' category of queries?

The 'Worse' category has a large effect on the overall benchmark performance

The 'Worse' category is the most frequent type of query

The 'Worse' category contains a majority of the queries

The 'Worse' category has minimal effect on the overall benchmark performance (correct)

In the example shown in Figure 21(a), what does the join graph depict?

The execution plan for QuerySplit and IEF Signup and view all the answers

What mistake does PostgreSQL’s optimizer make in estimating the cardinality of S1?

It underestimates the cardinality of S1 Signup and view all the answers

Which algorithm chose to execute S2 first instead of S1?

IEF Signup and view all the answers

What is the main advantage of QuerySplit compared to robust query processing baselines?

It is more efficient in handling cardinality estimation errors Signup and view all the answers

Why do learned cardinality estimation algorithms like NeuroCard and DeepDB achieve limited performance improvement?

They don't handle string columns efficiently Signup and view all the answers

What is the likely reason re-optimization is more effective and efficient than refining cardinality estimation in improving query performance?

It leads to query plans that are closer to optimal Signup and view all the answers

What is the reason behind USE having the same performance in both index configurations?

It disables nest-loop join, thus ignoring indexes in its query planning Signup and view all the answers