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Improve row count estimation for Limit/TopN #26088

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Tracked by #26085
time-and-fate opened this issue Jul 9, 2021 · 2 comments · Fixed by #26445
Closed
Tracked by #26085

Improve row count estimation for Limit/TopN #26088

time-and-fate opened this issue Jul 9, 2021 · 2 comments · Fixed by #26445
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sig/planner SIG: Planner type/enhancement The issue or PR belongs to an enhancement.

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@time-and-fate
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Currently, when doing row count estimation for the index/table scan in a SQL with LIMIT, we'll adjust the row count according to the LIMIT number and the correlation from statistics. This is a good strategy but sometimes it makes the planner choose TableScan when it should choose IndexScan, and the SQL execution becomes very slow. We'll try to fix it.
@time-and-fate time-and-fate added the type/enhancement The issue or PR belongs to an enhancement. label Jul 9, 2021
@time-and-fate time-and-fate mentioned this issue Jul 9, 2021
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@time-and-fate
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/sig planner

@ti-chi-bot ti-chi-bot added the sig/planner SIG: Planner label Jul 9, 2021
@qw4990 qw4990 mentioned this issue Jul 21, 2021
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qw4990 commented Jul 21, 2021

Please see #26445 for more examples and details.

This was referenced Jul 27, 2021
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sig/planner SIG: Planner type/enhancement The issue or PR belongs to an enhancement.
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planner: update the correlation adjustment rule of Limit/TopN for TableScan qw4990/tidb
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