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planner: adjust N used in TopN cost formula based on the total number of rows (#46368) #46571

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merged 3 commits into from
Oct 13, 2023
Merged

planner: adjust N used in TopN cost formula based on the total number of rows (#46368) #46571

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3871098
This is an automated cherry-pick of #46368
qw4990 Aug 31, 2023
7a3675c
fixup
qw4990 Oct 12, 2023
df06003
make linter happy
qw4990 Oct 13, 2023
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10 changes: 10 additions & 0 deletions planner/core/plan_cost_ver2.go
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Original file line number Diff line number Diff line change
Expand Up @@ -386,8 +386,18 @@ func (p *PhysicalTopN) getPlanCostVer2(taskType property.TaskType, option *PlanC
}

rows := getCardinality(p.children[0], option.CostFlag)
<<<<<<< HEAD
N := math.Max(1, float64(p.Count+p.Offset))
rowSize := getAvgRowSize(p.statsInfo(), p.Schema().Columns)
=======
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)
>>>>>>> 5fbe25ebe35 (planner: adjust N used in TopN cost formula based on the total number of rows (#46368))
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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Original file line number Diff line number Diff line change
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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