github.com/matrixorigin/matrixone@v0.7.0/pkg/sql/colexec/limit/limit.go (about)

     1  // Copyright 2021 Matrix Origin
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package limit
    16  
    17  import (
    18  	"bytes"
    19  	"fmt"
    20  
    21  	"github.com/matrixorigin/matrixone/pkg/container/batch"
    22  	"github.com/matrixorigin/matrixone/pkg/vm/process"
    23  )
    24  
    25  func String(arg any, buf *bytes.Buffer) {
    26  	n := arg.(*Argument)
    27  	buf.WriteString(fmt.Sprintf("limit(%v)", n.Limit))
    28  }
    29  
    30  func Prepare(_ *process.Process, _ any) error {
    31  	return nil
    32  }
    33  
    34  // Call returning only the first n tuples from its input
    35  func Call(idx int, proc *process.Process, arg any, isFirst bool, isLast bool) (bool, error) {
    36  	bat := proc.InputBatch()
    37  	if bat == nil {
    38  		return true, nil
    39  	}
    40  	if bat.Length() == 0 {
    41  		return false, nil
    42  	}
    43  	ap := arg.(*Argument)
    44  	anal := proc.GetAnalyze(idx)
    45  	anal.Start()
    46  	defer anal.Stop()
    47  	anal.Input(bat, isFirst)
    48  	if ap.Seen >= ap.Limit {
    49  		proc.Reg.InputBatch = nil
    50  		bat.Clean(proc.Mp())
    51  		return true, nil
    52  	}
    53  	length := bat.Length()
    54  	newSeen := ap.Seen + uint64(length)
    55  	if newSeen >= ap.Limit { // limit - seen
    56  		batch.SetLength(bat, int(ap.Limit-ap.Seen))
    57  		ap.Seen = newSeen
    58  		anal.Output(bat, isLast)
    59  		proc.SetInputBatch(bat)
    60  		return true, nil
    61  	}
    62  	anal.Output(bat, isLast)
    63  	ap.Seen = newSeen
    64  	return false, nil
    65  }