Fixed size of HashTable when Limit is used
Open
Nobody has claimed this yet.
type/enhancement
- Dominant language
- C++
- Stars
- 1k
- Forks
- 423
- Avg merge
- 1d 15h
- Merged PRs (30d)
- 24
Description
Enhancement
For table t1, assume the NDV of c1 of t1 is 100000.
For query like: select max(c1) from t1 group by c2 limit 100;
The HashTable of Aggregtion should be fixed 100 instead of 100000 because we only need 100 rows
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First steps
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Research direction
The issue names no implementation files or tests. Start by locating TiFlash's aggregation HashTable sizing path and reproduce the provided GROUP BY ... LIMIT query; done means the aggregation HashTable is sized for the LIMIT of 100 rather than the estimated NDV of 100000.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- databases, performance
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100