github.com/pingcap/ticdc@v0.0.0-20220526033649-485a10ef2652/cdc/processor/pipeline/mounter.go (about)

     1  // Copyright 2021 PingCAP, Inc.
     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  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package pipeline
    15  
    16  import (
    17  	"context"
    18  	"log"
    19  	"sync"
    20  	"time"
    21  
    22  	"github.com/edwingeng/deque"
    23  	"github.com/pingcap/failpoint"
    24  	"github.com/pingcap/ticdc/cdc/model"
    25  	"github.com/pingcap/ticdc/pkg/notify"
    26  	"github.com/pingcap/ticdc/pkg/pipeline"
    27  	"go.uber.org/zap"
    28  	"golang.org/x/sync/errgroup"
    29  	"golang.org/x/time/rate"
    30  )
    31  
    32  const (
    33  	waitEventMountedBatchSize = 128 * 1024 // larger means less CPU overhead used by `select` but more memory overhead.
    34  	maxNotificationsPerSecond = 10.0       // larger means lower latency, but more CPU used by `select`.
    35  )
    36  
    37  // mounterNode is now used to buffer unmounted events.
    38  // TODO rename this node, or refactor the mounter to make it synchronous.
    39  type mounterNode struct {
    40  	mu    sync.Mutex
    41  	queue deque.Deque // we use Deque for better memory consumption and support for batching
    42  
    43  	wg     errgroup.Group
    44  	cancel context.CancelFunc
    45  
    46  	// notifies new events pushed to the queue
    47  	notifier notify.Notifier
    48  	// limits the rate at which notifications are sent
    49  	rl *rate.Limiter
    50  }
    51  
    52  func newMounterNode() pipeline.Node {
    53  	return &mounterNode{
    54  		queue: deque.NewDeque(),
    55  		rl:    rate.NewLimiter(maxNotificationsPerSecond, 1 /* burst */),
    56  	}
    57  }
    58  
    59  func (n *mounterNode) Init(ctx pipeline.NodeContext) error {
    60  	stdCtx, cancel := context.WithCancel(ctx)
    61  	n.cancel = cancel
    62  
    63  	receiver, err := n.notifier.NewReceiver(time.Millisecond * 100)
    64  	if err != nil {
    65  		log.Panic("unexpected error", zap.Error(err))
    66  	}
    67  
    68  	n.wg.Go(func() error {
    69  		defer receiver.Stop()
    70  		for {
    71  			select {
    72  			case <-stdCtx.Done():
    73  				return nil
    74  			case <-receiver.C:
    75  				// handles writes to the queue
    76  				for {
    77  					n.mu.Lock()
    78  					msgs := n.queue.PopManyFront(waitEventMountedBatchSize)
    79  					n.mu.Unlock()
    80  					if len(msgs) == 0 {
    81  						break // inner loop
    82  					}
    83  
    84  					for _, msg := range msgs {
    85  						msg := msg.(pipeline.Message)
    86  						if msg.Tp != pipeline.MessageTypePolymorphicEvent {
    87  							// sends the control message directly to the next node
    88  							ctx.SendToNextNode(msg)
    89  							continue // to handling the next message
    90  						}
    91  
    92  						// handles PolymorphicEvents
    93  						event := msg.PolymorphicEvent
    94  						if event.RawKV.OpType != model.OpTypeResolved {
    95  							failpoint.Inject("MounterNodeWaitPrepare", func() {})
    96  							// only RowChangedEvents need mounting
    97  							err := event.WaitPrepare(stdCtx)
    98  							if err != nil {
    99  								ctx.Throw(err)
   100  								return nil
   101  							}
   102  						}
   103  
   104  						ctx.SendToNextNode(msg)
   105  					}
   106  				}
   107  			}
   108  		}
   109  	})
   110  
   111  	return nil
   112  }
   113  
   114  // Receive receives the message from the previous node
   115  func (n *mounterNode) Receive(ctx pipeline.NodeContext) error {
   116  	msg := ctx.Message()
   117  	n.mu.Lock()
   118  	n.queue.PushBack(msg)
   119  	n.mu.Unlock()
   120  
   121  	if n.rl.Allow() {
   122  		// send notification under the rate limiter
   123  		n.notifier.Notify()
   124  	}
   125  	return nil
   126  }
   127  
   128  func (n *mounterNode) Destroy(ctx pipeline.NodeContext) error {
   129  	defer n.notifier.Close()
   130  	n.cancel()
   131  	return n.wg.Wait()
   132  }