executor: parallel read inner table and build hash table.

executor/join.go

@@ -259,17 +259,37 @@ func (e *HashJoinExec) wait4Inner() (finished bool, err error) {
 
 // fetchInnerRows fetches all rows from inner executor,
 // and append them to e.innerResult.
-func (e *HashJoinExec) fetchInnerRows(ctx context.Context) (err error) {
+func (e *HashJoinExec) fetchInnerRows(ctx context.Context, chkCh chan<- *chunk.Chunk, doneCh chan struct{}) {
+	defer func() {
+		close(chkCh)
+		if r := recover(); r != nil {
+			buf := make([]byte, 4096)
+			stackSize := runtime.Stack(buf, false)
+			buf = buf[:stackSize]
+			log.Errorf("hash join inner fetcher panic stack is:\n%s", buf)
+		}
+	}()
 	e.innerResult = chunk.NewList(e.innerExec.retTypes(), e.maxChunkSize)
 	e.innerResult.GetMemTracker().AttachTo(e.memTracker)
 	e.innerResult.GetMemTracker().SetLabel("innerResult")
+	var err error
 	for {
-		chk := e.children[e.innerIdx].newChunk()
-		err = e.innerExec.Next(ctx, chk)
-		if err != nil || chk.NumRows() == 0 {
-			return errors.Trace(err)
+		select {
+		case <-doneCh:
+			return
+		default:
+			chk := e.children[e.innerIdx].newChunk()
+			err = e.innerExec.Next(ctx, chk)
+			if err != nil {
+				e.innerFinished <- errors.Trace(err)
+				return
+			}
+			if chk.NumRows() == 0 {
+				return
+			}
+			chkCh <- chk
+			e.innerResult.Add(chk)
 		}
-		e.innerResult.Add(chk)
 	}
 }
 
@@ -505,22 +525,28 @@ func (e *HashJoinExec) fetchInnerAndBuildHashTable(ctx context.Context) {
 		}
 		close(e.innerFinished)
 	}()
+	// innerResultCh transfer inner result chunk from inner fetch to build hash table.
+	innerResultCh := make(chan *chunk.Chunk, e.concurrency)
+	doneCh := make(chan struct{})
+	go e.fetchInnerRows(ctx, innerResultCh, doneCh)
 
-	if err := e.fetchInnerRows(ctx); err != nil {
-		e.innerFinished <- errors.Trace(err)
-		return
-	}
-
-	if err := e.buildHashTableForList(); err != nil {
+	// TODO: Parallel build hash table. Currently not support because `mvmap` is not thread-safe.
+	err := e.buildHashTableForList(innerResultCh)
+	if err != nil {
 		e.innerFinished <- errors.Trace(err)
-		return
+		close(doneCh)
+		// fetchInnerRows may be blocked by this channel, so read from the channel to unblock it.
+		select {
+		case <-innerResultCh:
+		default:
+		}
 	}
 }
 
 // buildHashTableForList builds hash table from `list`.
 // key of hash table: hash value of key columns
 // value of hash table: RowPtr of the corresponded row
-func (e *HashJoinExec) buildHashTableForList() error {
+func (e *HashJoinExec) buildHashTableForList(innerResultCh chan *chunk.Chunk) error {
 	e.hashTable = mvmap.NewMVMap()
 	e.innerKeyColIdx = make([]int, len(e.innerKeys))
 	for i := range e.innerKeys {
@@ -532,20 +558,23 @@ func (e *HashJoinExec) buildHashTableForList() error {
 		keyBuf  = make([]byte, 0, 64)
 		valBuf  = make([]byte, 8)
 	)
-	for i := 0; i < e.innerResult.NumChunks(); i++ {
-		chk := e.innerResult.GetChunk(i)
-		for j := 0; j < chk.NumRows(); j++ {
+
+	chkIdx := uint32(0)
+	for chk := range innerResultCh {
+		numRows := chk.NumRows()
+		for j := 0; j < numRows; j++ {
 			hasNull, keyBuf, err = e.getJoinKeyFromChkRow(false, chk.GetRow(j), keyBuf)
 			if err != nil {
 				return errors.Trace(err)
 			}
 			if hasNull {
 				continue
 			}
-			rowPtr := chunk.RowPtr{ChkIdx: uint32(i), RowIdx: uint32(j)}
+			rowPtr := chunk.RowPtr{ChkIdx: chkIdx, RowIdx: uint32(j)}
 			*(*chunk.RowPtr)(unsafe.Pointer(&valBuf[0])) = rowPtr
 			e.hashTable.Put(keyBuf, valBuf)
 		}
+		chkIdx++
 	}
 	return nil
 }