config: adjust puller config (#3473)

Author: asddongmen

pkg/config/debug.go

@@ -67,8 +67,8 @@ type PullerConfig struct {
 
 	// PendingRegionRequestQueueSize is the total size of the pending region request queue shared across
 	// all puller workers connecting to a single TiKV store. This size is divided equally among all workers.
-	// For example, if PendingRegionRequestQueueSize is 256 and there are 8 workers connecting to the same store,
-	// each worker's queue size will be 256 / 8 = 32.
+	// For example, if PendingRegionRequestQueueSize is 32 and there are 8 workers connecting to the same store,
+	// each worker's queue size will be 32 / 8 = 4.
 	PendingRegionRequestQueueSize int `toml:"pending-region-request-queue-size" json:"pending_region_request_queue_size"`
 }
 
@@ -78,7 +78,7 @@ func NewDefaultPullerConfig() *PullerConfig {
 		EnableResolvedTsStuckDetection: false,
 		ResolvedTsStuckInterval:        TomlDuration(5 * time.Minute),
 		LogRegionDetails:               false,
-		PendingRegionRequestQueueSize:  256, // Base on test result
+		PendingRegionRequestQueueSize:  32, // This value is chosen to reduce the impact of new changefeeds on existing ones.
 	}
 }