plan: support topn push down in plan phase. #1769

hanfei1991 · 2016-09-27T08:38:43Z

It's a additional pr for #1760
It tries to push topn to table scan and index scan.
@coocood @shenli @zimulala @tiancaiamao @XuHuaiyu PTAL

coocood · 2016-09-27T10:12:46Z

Any test covers the case when selection condition can not be converted to PB, then topN will not be pushed?

coocood · 2016-09-27T09:19:06Z

plan/physical_plans.go

@@ -114,6 +113,7 @@ func (p *physicalTableSource) addTopN(prop *requiredProperty) {
 	for _, item := range prop.props {
 		p.SortItems = append(p.SortItems, sortByItemToPB(p.client, item.col, item.desc))


sortByItem may return nil, then addTopN should return false.

hanfei1991 · 2016-09-27T12:46:39Z

@coocood PTAL

XuHuaiyu · 2016-09-28T08:58:46Z

plan/physical_plans.go

-	if prop.limit != nil {
-		count := int64(prop.limit.Count + prop.limit.Offset)
-		p.LimitCount = &count
+	if prop.limit == nil || len(prop.props) == 0 {


There may be no need to judge "prop.limit == nil", it has been promised before invoking this function.

It's safer to check this again inside this function.

XuHuaiyu · 2016-09-28T09:10:17Z

plan/physical_plans.go

@@ -74,6 +72,7 @@ type physicalTableSource struct {
 	AggFuncs   []*tipb.Expr
 	GbyItems   []*tipb.ByItem

+	// ConditionPBExpr is the pb structure of conditions that pushed down.


pushed down --> be pushed down

coocood · 2016-09-28T11:54:41Z

The added test case doesn't make much sense as the test use a mock context which returns a nil Client, and TopN is not supported by local store.
So TopN will never be pushed down.

hanfei1991 · 2016-09-29T03:21:05Z

@coocood PTAL

coocood · 2016-09-29T03:28:29Z

plan/plan_test.go

@@ -373,6 +535,10 @@ func (s *testPlanSuite) TestCBO(c *C) {
 			best: "Index(t.c_d_e)[[-inf,10000)]->Sort + Limit(2) + Offset(0)->Projection",
 		},
 		{
+			sql:  "select * from t a where a.c < 10000 and a.d in (1000, a.e) order by a.a limit 2",


move this case to TestTopnPushDown and verify that top n is not pushed down.

@hanfei1991

XuHuaiyu · 2016-09-29T12:09:33Z

plan/match_property.go

@@ -106,21 +141,38 @@ func (is *PhysicalIndexScan) matchProperty(prop *requiredProperty, infos ...*phy
 		if allAsc {


if allAsc || allDesc{ if allDesc { sortedIs.Desc = true } // Duplicated code }

would this be more brief

@hanfei1991

XuHuaiyu · 2016-09-30T03:43:39Z

Please take a look at function handleLeftJoin/handleRightJoin in physical_plan_builder.go, the local variable allLeft/allRight been checked if false three times, but if allLeft/allRight is false, the function will be returned just in the first check, and there is no value write of allLeft/allRight after this check.

shenli · 2016-09-30T08:41:13Z

executor/executor_distsql.go

-		selIdxReq.OrderBy = append(selIdxReq.OrderBy, &tipb.ByItem{Desc: e.indexPlan.Desc})
+	if len(e.indexPlan.SortItems) > 0 {
+		selIdxReq.OrderBy = e.indexPlan.SortItems
+	} else if e.indexPlan.Desc {


How about e.indexPlan.SortItems > 0 and e.indexPlan.Desc is true?

@hanfei1991

If e.indexPlan.SortItems > 0, we don't care if the table is desc scanned or not.

XuHuaiyu · 2016-09-30T08:52:24Z

plan/plan_test.go

@@ -46,6 +50,10 @@ func (s *testPlanSuite) SetUpSuite(c *C) {
 	s.Parser = parser.New()
 }

+func newType() types.FieldType {


newTypeLong() be better?

shenli · 2016-10-08T02:26:46Z

executor/executor_distsql.go

+	if len(e.orderByList) > 0 {
+		selReq.OrderBy = e.orderByList
+	} else if e.supportDesc && e.desc {
+		selReq.OrderBy = []*tipb.ByItem{{Desc: e.desc}}


When will e.desc is true and len(e.orderByList) == 0?

If no topn is pushed, the order by list will be empty.

shenli · 2016-10-08T02:30:28Z

plan/match_property.go

 	if len(prop.props) == 0 {
-		return enforceProperty(prop, &physicalPlanInfo{p: ts, cost: cost, count: infos[0].count})
+		p := tryToAddUnionScan(ts.txn, ts.conditions, ts)


Why add union scan here?

"try to add union scan" will check if the txn is read-only. If it is, it will add union scan for it.

shenli · 2016-10-08T02:33:30Z

plan/match_property.go

 	}
 	if len(prop.props) == 1 && ts.pkCol != nil && ts.pkCol == prop.props[0].col {
 		sortedTs := *ts
 		sortedTs.Desc = prop.props[0].desc
 		sortedTs.KeepOrder = true
+		p := tryToAddUnionScan(ts.txn, ts.conditions, &sortedTs)


Should we also addTopN in this condition?

This condition means the pk column can match the required property.

shenli · 2016-10-08T02:33:58Z

plan/match_property.go

@@ -106,21 +141,38 @@ func (is *PhysicalIndexScan) matchProperty(prop *requiredProperty, infos ...*phy
 		if allAsc {


@hanfei1991

shenli · 2016-10-08T02:36:11Z

plan/plan.go

@@ -259,12 +259,8 @@ func (p *basePlan) initID() {
 // basePlan implements base Plan interface.
 // Should be used as embedded struct in Plan implementations.
 type basePlan struct {
-	fields      []*ast.ResultField
-	startupCost float64
-	totalCost   float64


These attributes are useless?

shenli · 2016-10-08T02:36:48Z

plan/plan_test.go

@@ -46,6 +50,10 @@ func (s *testPlanSuite) SetUpSuite(c *C) {
 	s.Parser = parser.New()
 }

+func newType() types.FieldType {


newLongType is better.

shenli · 2016-10-08T02:37:03Z

plan/plan_test.go

@@ -373,6 +535,10 @@ func (s *testPlanSuite) TestCBO(c *C) {
 			best: "Index(t.c_d_e)[[-inf,10000)]->Sort + Limit(2) + Offset(0)->Projection",
 		},
 		{
+			sql:  "select * from t a where a.c < 10000 and a.d in (1000, a.e) order by a.a limit 2",


@hanfei1991

hanfei1991 · 2016-10-08T08:05:51Z

@shenli @coocood @XuHuaiyu PTAL

shenli · 2016-10-10T08:51:46Z

plan/physical_plan_builder.go

@@ -406,9 +385,6 @@ func (p *Join) handleLeftJoin(prop *requiredProperty, innerJoin bool) (*physical
 			allLeft = false
 		}
 	}
-	if !allLeft {


Make best effort to push down sort. Because if there is a limit and sort, it will be converted to top-n. Running top-n as early as possible will save running time.

shenli · 2016-10-10T08:52:45Z

LGTM

coocood · 2016-10-10T06:09:10Z

plan/physical_plans.go

@@ -54,15 +53,14 @@ type PhysicalIndexScan struct {

 	accessEqualCount int
 	AccessCondition  []expression.Expression
-	// ConditionPBExpr is the pb structure of conditions that pushed down.
-	ConditionPBExpr *tipb.Expr
+	conditions       []expression.Expression

 	TableAsName *model.CIStr
 }

 type physicalDistSQLPlan interface {


Add comment about this interface and the methods, describe why we need this interface, how those method should be implemented and used.

coocood · 2016-10-10T06:20:05Z

plan/physical_plans.go

@@ -40,7 +39,7 @@ type PhysicalIndexScan struct {
 	basePlan
 	physicalTableSource

-	ctx        context.Context
+	txn        kv.Transaction


We don't need to keep a txn reference, we only need to know if it is read only.

coocood · 2016-10-10T06:21:05Z

plan/physical_plans.go

@@ -178,7 +179,7 @@ type PhysicalTableScan struct {
 	basePlan
 	physicalTableSource

-	ctx     context.Context
+	txn     kv.Transaction


coocood · 2016-10-11T03:44:38Z

LGTM

support topn in plan phase.

5673491

hanfei1991 changed the title ~~support topn in plan phase.~~ plan: support topn push down in plan phase. Sep 27, 2016

coocood reviewed Sep 27, 2016

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add test

f7eedaf

XuHuaiyu reviewed Sep 28, 2016

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add test.

c0cd833

hanfei1991 force-pushed the hanfei/topn branch from 731e8ef to c0cd833 Compare September 29, 2016 03:25

coocood reviewed Sep 29, 2016

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XuHuaiyu reviewed Sep 29, 2016

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shenli reviewed Sep 30, 2016

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XuHuaiyu reviewed Sep 30, 2016

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shenli reviewed Oct 8, 2016

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hanfei1991 added 3 commits October 8, 2016 14:17

tiny change.

b52d6b0

Merge branch 'master' into hanfei/topn

d87dbf4

tiny change.

3d6faad

shenli reviewed Oct 10, 2016

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coocood reviewed Oct 10, 2016

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address comment.

967c560

Merge branch 'master' into hanfei/topn

0382a65

hanfei1991 merged commit 9b9c011 into master Oct 11, 2016

hanfei1991 deleted the hanfei/topn branch October 11, 2016 07:17

		@@ -114,6 +113,7 @@ func (p physicalTableSource) addTopN(prop requiredProperty) {
		for _, item := range prop.props {
		p.SortItems = append(p.SortItems, sortByItemToPB(p.client, item.col, item.desc))

		@@ -106,21 +141,38 @@ func (is PhysicalIndexScan) matchProperty(prop requiredProperty, infos ...*phy
		if allAsc {

plan: support topn push down in plan phase. #1769

plan: support topn push down in plan phase. #1769

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hanfei1991 commented Sep 27, 2016

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coocood commented Sep 28, 2016

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hanfei1991 commented Oct 8, 2016

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coocood commented Oct 11, 2016

coocood commented Sep 27, 2016 •

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XuHuaiyu Sep 28, 2016 •

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XuHuaiyu Sep 29, 2016 •

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