expression: speed up Column.VecEvalReal by using MergeNulls

[Tjianke]

What problem does this PR solve?

Issue Number: close #22190

Problem Summary:

improve efficiency of Column.VecEvalReal() with Column.MergeNulls()

What is changed and how it works?

What's Changed:

expression/column.go: use Column.MergeNulls() before copying src element to result

Related changes

Tests

• Unit test

Benchmark

use BenchmarkVectorizedBuiltinArithmeticFunc to benchmark

go test --timeout 0 -v -benchmem -bench=BenchmarkVecEvalReal -count=20 -run=BenchmarkVecEvalReal | tee old.txt
go test --timeout 0 -v -benchmem -bench=BenchmarkVecEvalReal -count=20 -run=BenchmarkVecEvalReal | tee new.txt

benchstat old.txt new.txt
name                       old time/op    new time/op    delta
VecEvalReal/VecEvalReal-2    0.39ns ± 5%    0.38ns ± 6%  -2.44%  (p=0.003 n=18+20)

name                       old alloc/op   new alloc/op   delta
VecEvalReal/VecEvalReal-2     0.00B          0.00B         ~     (all equal)

name                       old allocs/op  new allocs/op  delta
VecEvalReal/VecEvalReal-2      0.00           0.00         ~     (all equal)

benchmark func:

func BenchmarkVecEvalReal(b *testing.B){
	ctx := mock.NewContext()

	batchSize := []int{
		10,
		100,
		1000,
		100000,
	}

	for i:=0; i<len(batchSize); i++ {
		ft := types.NewFieldType(mysql.TypeFloat)
		col := &Column{RetType: ft, Index: 0}
		input := chunk.New([]*types.FieldType{ft}, batchSize[i], batchSize[i])
		for i := 0; i < batchSize[i]; i++ {
			input.AppendFloat32(0, float32(i))
		}
		result, err := newBuffer(types.ETReal, batchSize[i])
		if err != nil {
			panic(err)
		}
		b.Run(fmt.Sprintf("origin-%d", batchSize[i]), func(b *testing.B){
			col.VecEvalReal(ctx, input, result)
		})
		result, err = newBuffer(types.ETReal, batchSize[i])
	}
}

Release note

• speed up VecEvalReal() with MergeNulls()

Reference

Another PR that utilized MergeNulls() to speed up functions #12674

[Tjianke]

/run-all-tests

[Tjianke]

/run-all-tests

[Tjianke]

/run-all-tests

[Tjianke]

Some question about tests in TiDB

Had a really difficult time to debug a randgen integration test, anyway to view the integration test or to provide more info on failed tests?

for instance, in this integration test, I could barely get anything useful except from panic info I hardcoded inside.

[ngaut]

PTAL @zhouqiang-cl

[zhouqiang-cl]

PTAL @zhouqiang-cl

Got, we will improve it. /cc @Tjianke

[Tjianke]

@lzmhhh123 @qw4990 PTAL, thanks~

[lzmhhh123]

LGTM

[Tjianke]

@qw4990 PTAL, thanks~

[b41sh]

LGTM

[lzmhhh123]

/merge

[ti-srebot]

/run-all-tests

[ti-srebot]

@Tjianke merge failed.

[Tjianke]

/run-all-tests