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planner: adjust N used in TopN cost formula based on the total number of rows #46368

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merged 6 commits into from
Aug 31, 2023
Merged

planner: adjust N used in TopN cost formula based on the total number of rows #46368

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b2fe09b
fixup
qw4990 Aug 23, 2023
cd1a896
make linter happy
qw4990 Aug 31, 2023
68958f9
make linter happy
qw4990 Aug 31, 2023
37c21c9
make linter happy
qw4990 Aug 31, 2023
4911791
make linter happy
qw4990 Aug 31, 2023
0bf2e67
make linter happy
qw4990 Aug 31, 2023
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7 changes: 6 additions & 1 deletion planner/core/plan_cost_ver2.go
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Original file line number Diff line number Diff line change
Expand Up @@ -395,7 +395,12 @@ func (p *PhysicalTopN) getPlanCostVer2(taskType property.TaskType, option *PlanC
}

rows := getCardinality(p.children[0], option.CostFlag)
n := math.Max(1, float64(p.Count+p.Offset))
n := max(1, float64(p.Count+p.Offset))
if n > 10000 {
// It's only used to prevent some extreme cases, e.g. `select * from t order by a limit 18446744073709551615`.
// For normal cases, considering that `rows` may be under-estimated, better to keep `n` unchanged.
n = min(n, rows)
}
rowSize := getAvgRowSize(p.StatsInfo(), p.Schema().Columns)
cpuFactor := getTaskCPUFactorVer2(p, taskType)
memFactor := getTaskMemFactorVer2(p, taskType)
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12 changes: 12 additions & 0 deletions planner/core/plan_cost_ver2_test.go
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Expand Up @@ -53,6 +53,18 @@ func testCostQueries(t *testing.T, tk *testkit.TestKit, queries []string) {
}
}

func TestHugeTopNCost(t *testing.T) {
store := testkit.CreateMockStore(t)
tk := testkit.NewTestKit(t, store)
tk.MustExec("use test")
tk.MustExec(`create table t (a int)`)
tk.MustExec(`insert into t values (1)`)
tk.MustExec(`analyze table t`)
plan1 := tk.MustQuery("explain format='verbose' select /*+ limit_to_cop() */ * from t where a=1 order by a limit 1")
plan2 := tk.MustQuery("explain format='verbose' select /*+ limit_to_cop() */ * from t where a=1 order by a limit 1000000000")
require.Equal(t, plan1.Rows()[0][2], plan2.Rows()[0][2]) // should have the same plan cost
}

func TestCostModelVer2(t *testing.T) {
store := testkit.CreateMockStore(t)
tk := testkit.NewTestKit(t, store)
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