Add EventCacheCount as member of BinlogSyncerConfig to limit streamer's event channel size (#830)

* lower memory usage by reducing event chan size in streamer

When consuming events from stream is blocked, the chan may use too much memory

* make streamer's event chan size configurable

When the consumption speed of the event chan in streamer cannot catch up with its production speed, leading to an accumulation of events, the current fixed channel size of 10240 might occupy significant memory, potentially triggering an Out Of Memory (OOM) condition. Making the size of the event chan configurable would allow for controlling the memory usage of the streamer.

* update cfg name StreamerChanSize to EventCacheSize

* EventCacheSize is renamed to EventCacheCount, to make the variable name more reflective of its actual meaning.

Author: zing22845

replication/binlogstreamer.go

@@ -85,9 +85,17 @@ func (s *BinlogStreamer) closeWithError(err error) {
 }
 
 func NewBinlogStreamer() *BinlogStreamer {
+	return NewBinlogStreamerWithChanSize(10240)
+}
+
+func NewBinlogStreamerWithChanSize(chanSize int) *BinlogStreamer {
 	s := new(BinlogStreamer)
 
-	s.ch = make(chan *BinlogEvent, 10240)
+	if chanSize <= 0 {
+		chanSize = 10240
+	}
+
+	s.ch = make(chan *BinlogEvent, chanSize)
 	s.ech = make(chan error, 4)
 
 	return s

replication/binlogsyncer.go

@@ -122,6 +122,8 @@ type BinlogSyncerConfig struct {
 	RowsEventDecodeFunc func(*RowsEvent, []byte) error
 
 	DiscardGTIDSet bool
+
+	EventCacheCount int
 }
 
 // BinlogSyncer syncs binlog event from server.
@@ -166,6 +168,9 @@ func NewBinlogSyncer(cfg BinlogSyncerConfig) *BinlogSyncer {
 		dialer := &net.Dialer{}
 		cfg.Dialer = dialer.DialContext
 	}
+	if cfg.EventCacheCount == 0 {
+		cfg.EventCacheCount = 10240
+	}
 
 	// Clear the Password to avoid outputing it in log.
 	pass := cfg.Password
@@ -393,7 +398,7 @@ func (b *BinlogSyncer) prepare() error {
 func (b *BinlogSyncer) startDumpStream() *BinlogStreamer {
 	b.running = true
 
-	s := NewBinlogStreamer()
+	s := NewBinlogStreamerWithChanSize(b.cfg.EventCacheCount)
 
 	b.wg.Add(1)
 	go b.onStream(s)