Skip to content

Commit

Permalink
planner: adjust N used in TopN cost formula based on the total number…
Browse files Browse the repository at this point in the history
… of rows (#46368)

close #43285
  • Loading branch information
qw4990 authored Aug 31, 2023
1 parent dba010d commit 5fbe25e
Show file tree
Hide file tree
Showing 2 changed files with 18 additions and 1 deletion.
7 changes: 6 additions & 1 deletion planner/core/plan_cost_ver2.go
Original file line number Diff line number Diff line change
Expand Up @@ -396,7 +396,12 @@ 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)
Expand Down
12 changes: 12 additions & 0 deletions planner/core/plan_cost_ver2_test.go
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)
Expand Down

0 comments on commit 5fbe25e

Please sign in to comment.