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Optimizer: derive TopN from filter on row number (#41209)
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// Copyright 2023 PingCAP, Inc. | ||
// | ||
// Licensed under the Apache License, Version 2.0 (the "License"); | ||
// you may not use this file except in compliance with the License. | ||
// You may obtain a copy of the License at | ||
// | ||
// http://www.apache.org/licenses/LICENSE-2.0 | ||
// | ||
// Unless required by applicable law or agreed to in writing, software | ||
// distributed under the License is distributed on an "AS IS" BASIS, | ||
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
// See the License for the specific language governing permissions and | ||
// limitations under the License. | ||
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package core | ||
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import ( | ||
"context" | ||
"fmt" | ||
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"github.com/pingcap/tidb/expression" | ||
"github.com/pingcap/tidb/parser/ast" | ||
"github.com/pingcap/tidb/planner/util" | ||
) | ||
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// deriveTopNFromWindow pushes down the topN or limit. In the future we will remove the limit from `requiredProperty` in CBO phase. | ||
type deriveTopNFromWindow struct { | ||
} | ||
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func appendDerivedTopNTrace(topN LogicalPlan, opt *logicalOptimizeOp) { | ||
child := topN.Children()[0] | ||
action := func() string { | ||
return fmt.Sprintf("%v_%v top N added below %v_%v ", topN.TP(), topN.ID(), child.TP(), child.ID()) | ||
} | ||
reason := func() string { | ||
return fmt.Sprintf("%v filter on row number", topN.TP()) | ||
} | ||
opt.appendStepToCurrent(topN.ID(), topN.TP(), reason, action) | ||
} | ||
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/* | ||
Check the following pattern of filter over row number window function: | ||
- Filter is simple condition of row_number < value or row_number <= value | ||
- The window function is a simple row number | ||
- With default frame: rows between current row and current row. Check is not necessary since | ||
current row is only frame applicable to row number | ||
- No partition | ||
- Child is a data source. | ||
*/ | ||
func windowIsTopN(p *LogicalSelection) (bool, uint64) { | ||
// Check if child is window function. | ||
child, isLogicalWindow := p.Children()[0].(*LogicalWindow) | ||
if !isLogicalWindow { | ||
return false, 0 | ||
} | ||
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if len(p.Conditions) != 1 { | ||
return false, 0 | ||
} | ||
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// Check if filter is column < constant or column <= constant. If it is in this form find column and constant. | ||
column, limitValue := expression.FindUpperBound(p.Conditions[0]) | ||
if column == nil || limitValue <= 0 { | ||
return false, 0 | ||
} | ||
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// Check if filter on window function | ||
windowColumns := child.GetWindowResultColumns() | ||
if len(windowColumns) != 1 || !(column.Equal(p.ctx, windowColumns[0])) { | ||
return false, 0 | ||
} | ||
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grandChild := child.Children()[0] | ||
_, isDataSource := grandChild.(*DataSource) | ||
if !isDataSource { | ||
return false, 0 | ||
} | ||
if len(child.WindowFuncDescs) == 1 && child.WindowFuncDescs[0].Name == "row_number" && len(child.PartitionBy) == 0 && | ||
child.Frame.Type == ast.Rows && child.Frame.Start.Type == ast.CurrentRow && child.Frame.End.Type == ast.CurrentRow { | ||
return true, uint64(limitValue) | ||
} | ||
return false, 0 | ||
} | ||
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func (s *deriveTopNFromWindow) optimize(_ context.Context, p LogicalPlan, opt *logicalOptimizeOp) (LogicalPlan, error) { | ||
return p.deriveTopN(opt), nil | ||
} | ||
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func (s *baseLogicalPlan) deriveTopN(opt *logicalOptimizeOp) LogicalPlan { | ||
p := s.self | ||
for i, child := range p.Children() { | ||
newChild := child.deriveTopN(opt) | ||
p.SetChild(i, newChild) | ||
} | ||
return p | ||
} | ||
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func (s *LogicalSelection) deriveTopN(opt *logicalOptimizeOp) LogicalPlan { | ||
p := s.self.(*LogicalSelection) | ||
windowIsTopN, limitValue := windowIsTopN(p) | ||
if windowIsTopN { | ||
child := p.Children()[0].(*LogicalWindow) | ||
grandChild := child.Children()[0].(*DataSource) | ||
// Build order by for derived Limit | ||
byItems := make([]*util.ByItems, 0, len(child.OrderBy)) | ||
for _, col := range child.OrderBy { | ||
byItems = append(byItems, &util.ByItems{Expr: col.Col, Desc: col.Desc}) | ||
} | ||
// Build derived Limit | ||
derivedTopN := LogicalTopN{Count: limitValue, ByItems: byItems}.Init(grandChild.ctx, grandChild.blockOffset) | ||
derivedTopN.SetChildren(grandChild) | ||
/* return datasource->topN->window */ | ||
child.SetChildren(derivedTopN) | ||
appendDerivedTopNTrace(child, opt) | ||
return child | ||
} | ||
return p | ||
} | ||
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func (*deriveTopNFromWindow) name() string { | ||
return "derive_topn_from_window" | ||
} |
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// Copyright 2023 PingCAP, Inc. | ||
// | ||
// Licensed under the Apache License, Version 2.0 (the "License"); | ||
// you may not use this file except in compliance with the License. | ||
// You may obtain a copy of the License at | ||
// | ||
// http://www.apache.org/licenses/LICENSE-2.0 | ||
// | ||
// Unless required by applicable law or agreed to in writing, software | ||
// distributed under the License is distributed on an "AS IS" BASIS, | ||
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
// See the License for the specific language governing permissions and | ||
// limitations under the License. | ||
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package core_test | ||
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import ( | ||
"testing" | ||
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plannercore "github.com/pingcap/tidb/planner/core" | ||
"github.com/pingcap/tidb/testkit" | ||
"github.com/pingcap/tidb/testkit/testdata" | ||
) | ||
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// Rule should bot be applied | ||
func TestPushDerivedTopnNegative(t *testing.T) { | ||
store := testkit.CreateMockStore(t) | ||
tk := testkit.NewTestKit(t, store) | ||
tk.MustExec("use test") | ||
tk.MustExec("drop table if exists employee") | ||
tk.MustExec("create table t(a int, b int)") | ||
tk.MustExec("insert into t values(1,1)") | ||
tk.MustExec("insert into t values(2,1)") | ||
tk.MustExec("insert into t values(3,2)") | ||
tk.MustExec("insert into t values(4,2)") | ||
tk.MustExec("insert into t values(5,2)") | ||
var input Input | ||
var output []struct { | ||
SQL string | ||
Plan []string | ||
} | ||
suiteData := plannercore.GetDerivedTopNSuiteData() | ||
suiteData.LoadTestCases(t, &input, &output) | ||
for i, sql := range input { | ||
plan := tk.MustQuery("explain format = 'brief' " + sql) | ||
testdata.OnRecord(func() { | ||
output[i].SQL = sql | ||
output[i].Plan = testdata.ConvertRowsToStrings(plan.Rows()) | ||
}) | ||
plan.Check(testkit.Rows(output[i].Plan...)) | ||
} | ||
} | ||
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// Rule should be applied | ||
func TestPushDerivedTopnPositive(t *testing.T) { | ||
store := testkit.CreateMockStore(t) | ||
tk := testkit.NewTestKit(t, store) | ||
tk.MustExec("use test") | ||
tk.MustExec("drop table if exists employee") | ||
tk.MustExec("create table t(a int, b int)") | ||
tk.MustExec("insert into t values(1,1)") | ||
tk.MustExec("insert into t values(2,1)") | ||
tk.MustExec("insert into t values(3,2)") | ||
tk.MustExec("insert into t values(4,2)") | ||
tk.MustExec("insert into t values(5,2)") | ||
var input Input | ||
var output []struct { | ||
SQL string | ||
Plan []string | ||
Res []string | ||
} | ||
suiteData := plannercore.GetDerivedTopNSuiteData() | ||
suiteData.LoadTestCases(t, &input, &output) | ||
for i, sql := range input { | ||
plan := tk.MustQuery("explain format = 'brief' " + sql) | ||
res := tk.MustQuery(sql) | ||
testdata.OnRecord(func() { | ||
output[i].SQL = sql | ||
output[i].Plan = testdata.ConvertRowsToStrings(plan.Rows()) | ||
output[i].Res = testdata.ConvertRowsToStrings(res.Rows()) | ||
}) | ||
plan.Check(testkit.Rows(output[i].Plan...)) | ||
res.Check(testkit.Rows(output[i].Res...)) | ||
} | ||
} |
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[ | ||
{ | ||
"name": "TestPushDerivedTopnNegative", | ||
"cases":[ | ||
"select row_number() over (partition by a) from t -- pattern missing filter on row number", | ||
"select * from (select rank() over () as rank_order from t) DT where rank_order <= 3 -- rank not supported in pattern yet", | ||
"select * from (select row_number() over (partition by a) as rownumber from t) DT where rownumber <= 3 -- pattern is applicable but partition by is not supported yet", | ||
"select * from (select row_number() over () as rownumber1, row_number() over (partition by a) as rownumber2 from t) DT where rownumber1 <= 3 -- pattern not applicable with multiple window functions", | ||
"select * from (select b, row_number() over () as rownumber from t) DT where rownumber <= 3 and b > 5 -- pattern is not applicable with complex filter on top of window", | ||
"select * from (select b, row_number() over () as rownumber from t) DT where rownumber > 3 -- pattern is not applicable with filter is not < or <=", | ||
"select * from (select a,b, row_number() over () as rownumber from t) DT where a > b -- pattern is not applicable with filter is not < or <=", | ||
"select * from (select a,b, row_number() over () as rownumber from t) DT where a <= 3 -- pattern is not applicable with filter is not on row number", | ||
"select * from (select a,b, row_number() over () as rownumber from t) DT where 3 >= rownumber -- pattern is not applicable with filter is not < or <=", | ||
"select * from (select a,b, row_number() over () as rownumber from t) DT where rownumber <= -4 -- pattern is not applicable with filter constant negative", | ||
"select * from (select row_number() over () as rownumber from t) DT where rownumber <= 3 and rownumber >= 2 -- pattern is not applicable with complex filter" | ||
] | ||
}, | ||
{ | ||
"name": "TestPushDerivedTopnPositive", | ||
"cases":[ | ||
"select * from (select a,b, row_number() over (order by a) as rownumber from t) DT where rownumber <= 3.5 -- pattern is applicable with N rounded down to an integer", | ||
"select * from (select row_number() over (order by a) as rownumber from t) DT where rownumber <= 3 -- pattern is applicable", | ||
"select * from (select row_number() over (order by a) as rownumber from t) DT where rownumber < 3 -- pattern is applicable", | ||
"select * from (select row_number() over(rows between 1 preceding and 1 following) as rownumber from t) DT where rownumber <= 3 -- pattern is applicable", | ||
"select * from (select a,row_number() over (order by a desc) as rownumber,b from t) DT where rownumber <= 3 -- pattern is applicable", | ||
"select count(*) from (select * from (select a,row_number() over (order by b) as rownumber,b from t) DT1 where rownumber <= 1) DT2 -- pattern is applicable" | ||
] | ||
} | ||
] |
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