From af5934d2642ba26f5a7a82ac60e9d1e3fa9d07ce Mon Sep 17 00:00:00 2001
From: xuhuaiyu <391585975@qq.com>
Date: Fri, 12 Mar 2021 11:33:00 +0800
Subject: [PATCH] Revert "executor: open childExec during execution for
 UnionExec (#21561)"

This reverts commit 0eb8ff97bc1177fd9ac62f2d925eeec196211036.
---
 executor/executor.go      | 43 ++++-----------------------------------
 executor/executor_test.go | 34 -------------------------------
 2 files changed, 4 insertions(+), 73 deletions(-)

diff --git a/executor/executor.go b/executor/executor.go
index 3303436c39a44..201ef2e248f56 100644
--- a/executor/executor.go
+++ b/executor/executor.go
@@ -28,7 +28,6 @@ import (
 	"github.com/cznic/mathutil"
 	"github.com/opentracing/opentracing-go"
 	"github.com/pingcap/errors"
-	"github.com/pingcap/failpoint"
 	"github.com/pingcap/parser/ast"
 	"github.com/pingcap/parser/auth"
 	"github.com/pingcap/parser/model"
@@ -1442,12 +1441,6 @@ type UnionExec struct {
 	results     []*chunk.Chunk
 	wg          sync.WaitGroup
 	initialized bool
-	mu          struct {
-		*sync.Mutex
-		maxOpenedChildID int
-	}
-
-	childInFlightForTest int32
 }
 
 // unionWorkerResult stores the result for a union worker.
@@ -1467,11 +1460,12 @@ func (e *UnionExec) waitAllFinished() {
 
 // Open implements the Executor Open interface.
 func (e *UnionExec) Open(ctx context.Context) error {
+	if err := e.baseExecutor.Open(ctx); err != nil {
+		return err
+	}
 	e.stopFetchData.Store(false)
 	e.initialized = false
 	e.finished = make(chan struct{})
-	e.mu.Mutex = &sync.Mutex{}
-	e.mu.maxOpenedChildID = -1
 	return nil
 }
 
@@ -1517,19 +1511,6 @@ func (e *UnionExec) resultPuller(ctx context.Context, workerID int) {
 		e.wg.Done()
 	}()
 	for childID := range e.childIDChan {
-		e.mu.Lock()
-		if childID > e.mu.maxOpenedChildID {
-			e.mu.maxOpenedChildID = childID
-		}
-		e.mu.Unlock()
-		if err := e.children[childID].Open(ctx); err != nil {
-			result.err = err
-			e.stopFetchData.Store(true)
-			e.resultPool <- result
-		}
-		failpoint.Inject("issue21441", func() {
-			atomic.AddInt32(&e.childInFlightForTest, 1)
-		})
 		for {
 			if e.stopFetchData.Load().(bool) {
 				return
@@ -1544,20 +1525,12 @@ func (e *UnionExec) resultPuller(ctx context.Context, workerID int) {
 				e.resourcePools[workerID] <- result.chk
 				break
 			}
-			failpoint.Inject("issue21441", func() {
-				if int(atomic.LoadInt32(&e.childInFlightForTest)) > e.concurrency {
-					panic("the count of child in flight is larger than e.concurrency unexpectedly")
-				}
-			})
 			e.resultPool <- result
 			if result.err != nil {
 				e.stopFetchData.Store(true)
 				return
 			}
 		}
-		failpoint.Inject("issue21441", func() {
-			atomic.AddInt32(&e.childInFlightForTest, -1)
-		})
 	}
 }
 
@@ -1596,15 +1569,7 @@ func (e *UnionExec) Close() error {
 		for range e.childIDChan {
 		}
 	}
-	// We do not need to acquire the e.mu.Lock since all the resultPuller can be
-	// promised to exit when reaching here (e.childIDChan been closed).
-	var firstErr error
-	for i := 0; i <= e.mu.maxOpenedChildID; i++ {
-		if err := e.children[i].Close(); err != nil && firstErr == nil {
-			firstErr = err
-		}
-	}
-	return firstErr
+	return e.baseExecutor.Close()
 }
 
 // ResetContextOfStmt resets the StmtContext and session variables.
diff --git a/executor/executor_test.go b/executor/executor_test.go
index 1b90e1f79375a..aff376228b938 100644
--- a/executor/executor_test.go
+++ b/executor/executor_test.go
@@ -7399,40 +7399,6 @@ func (s *testSuite) TestOOMActionPriority(c *C) {
 	c.Assert(action.GetPriority(), Equals, int64(memory.DefLogPriority))
 }
 
-func (s *testSerialSuite) TestIssue21441(c *C) {
-	err := failpoint.Enable("github.com/pingcap/tidb/executor/issue21441", `return`)
-	c.Assert(err, IsNil)
-	defer func() {
-		err := failpoint.Disable("github.com/pingcap/tidb/executor/issue21441")
-		c.Assert(err, IsNil)
-	}()
-
-	tk := testkit.NewTestKit(c, s.store)
-	tk.MustExec("use test")
-	tk.MustExec("drop table if exists t")
-	tk.MustExec("create table t(a int)")
-	tk.MustExec(`insert into t values(1),(2),(3)`)
-	tk.Se.GetSessionVars().InitChunkSize = 1
-	tk.Se.GetSessionVars().MaxChunkSize = 1
-	sql := `
-select a from t union all
-select a from t union all
-select a from t union all
-select a from t union all
-select a from t union all
-select a from t union all
-select a from t union all
-select a from t`
-	tk.MustQuery(sql).Sort().Check(testkit.Rows(
-		"1", "1", "1", "1", "1", "1", "1", "1",
-		"2", "2", "2", "2", "2", "2", "2", "2",
-		"3", "3", "3", "3", "3", "3", "3", "3",
-	))
-
-	tk.MustQuery("select a from (" + sql + ") t order by a limit 4").Check(testkit.Rows("1", "1", "1", "1"))
-	tk.MustQuery("select a from (" + sql + ") t order by a limit 7, 4").Check(testkit.Rows("1", "2", "2", "2"))
-}
-
 func (s *testSuite) Test17780(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")