*: reduce memory consumption by reducing channel sizes (#1999)

cdc/kv/region_worker.go

@@ -39,13 +39,9 @@ import (
 )
 
 var (
-	regionWorkerPool workerpool.WorkerPool
-	workerPoolOnce   sync.Once
-	// The magic number here is keep the same with some magic numbers in some
-	// other components in TiCDC, including worker pool task chan size, mounter
-	// chan size etc.
-	// TODO: unified channel buffer mechanism
-	regionWorkerInputChanSize = 128000
+	regionWorkerPool          workerpool.WorkerPool
+	workerPoolOnce            sync.Once
+	regionWorkerInputChanSize = 128
 	regionWorkerLowWatermark  = int(float64(regionWorkerInputChanSize) * 0.2)
 	regionWorkerHighWatermark = int(float64(regionWorkerInputChanSize) * 0.7)
 )

pkg/workerpool/pool_impl.go

@@ -260,7 +260,7 @@ type worker struct {
 
 func newWorker() *worker {
 	return &worker{
-		taskCh:         make(chan *task, 128000),
+		taskCh:         make(chan *task, 128),
 		handles:        make(map[*defaultEventHandle]struct{}),
 		handleCancelCh: make(chan struct{}), // this channel must be unbuffered, i.e. blocking
 	}