Lower CPU usage at idle by reducing db polling

model/model.go

@@ -872,3 +872,18 @@ func (m *Model) Override(repo string) {
 
 	r.Update(cid.LocalID, fs)
 }
+
+// Version returns the change version for the given repository. This is
+// guaranteed to increment if the contents of the local or global repository
+// has changed.
+func (m *Model) Version(repo string) uint64 {
+	var ver uint64
+
+	m.rmut.Lock()
+	for _, n := range m.repoNodes[repo] {
+		ver += m.repoFiles[repo].Changes(m.cm.Get(n))
+	}
+	m.rmut.Unlock()
+
+	return ver
+}

model/puller.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"time"
+
 	"github.com/calmh/syncthing/cid"
 	"github.com/calmh/syncthing/config"
 	"github.com/calmh/syncthing/osutil"
@@ -135,6 +136,7 @@ func (p *puller) run() {
 	walkTicker := time.Tick(time.Duration(p.cfg.Options.RescanIntervalS) * time.Second)
 	timeout := time.Tick(5 * time.Second)
 	changed := true
+	var prevVer uint64
 
 	for {
 		// Run the pulling loop as long as there are blocks to fetch
@@ -197,8 +199,11 @@ func (p *puller) run() {
 		default:
 		}
 
-		// Queue more blocks to fetch, if any
-		p.queueNeededBlocks()
+		if v := p.model.Version(p.repoCfg.ID); v > prevVer {
+			// Queue more blocks to fetch, if any
+			p.queueNeededBlocks()
+			prevVer = v
+		}
 	}
 }