plan: forbid limit to push across selection. #2793
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coocood
reviewed
Mar 8, 2017
| @@ -855,6 +866,8 @@ func (p *Selection) convert2PhysicalPlanEnforce(prop *requiredProperty) (*physic | |||
| if prop.limit != nil && len(prop.props) > 0 { | |||
| if t, ok := info.p.(physicalDistSQLPlan); ok { | |||
| t.addTopN(p.ctx, prop) | |||
| } else if _, ok := info.p.(*Selection); !ok { | |||
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If the child info is *Selection, the Selection p will be lost?
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If child is selection, it means the selection has been processed
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Oh, I remembered, the child has pulled the parent Selection down.
This design is anti-pattern.
coocood
reviewed
Mar 8, 2017
| np.SetChildren(childPlanInfo[0].p) | ||
| count := uint64(float64(childPlanInfo[0].count) * selectionFactor) | ||
| return &physicalPlanInfo{p: &np, cost: childPlanInfo[0].cost, count: count} | ||
| return childPlanInfo[0] |
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Here the childPlanInfo is actually not child, it is the selection itself?
Then the matchProperty is not used as it is supposed to be.
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Yeah, in case of not on table, it's the selection itself.
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LGTM |
1 similar comment
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LGTM |
coocood
approved these changes
Mar 8, 2017
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When the SQL is
Select * from t left join s on true where least(1,2,3,t1.a,t2.b) > 0 order by t2.a limit 10, the old plan isJoin(t,s)->TopN->Selection, it's wrong. After fixing it, the plan isJoin(t,s)->Selection->TopN.@shenli @coocood @zimulala PTAL