enable concurrent writing explicitly

import_/import.go

@@ -167,6 +167,7 @@ func Import() {
 		relWriter := writer.NewRelationWriter(osmCache, diffCache, relations,
 			db, progress, config.BaseOptions.Srid)
 		relWriter.SetLimiter(geometryLimiter)
+		relWriter.EnableConcurrent()
 		relWriter.Start()
 		relWriter.Wait() // blocks till the Relations.Iter() finishes
 		osmCache.Relations.Close()
@@ -175,6 +176,7 @@ func Import() {
 		wayWriter := writer.NewWayWriter(osmCache, diffCache, ways, db,
 			progress, config.BaseOptions.Srid)
 		wayWriter.SetLimiter(geometryLimiter)
+		wayWriter.EnableConcurrent()
 		wayWriter.Start()
 		wayWriter.Wait() // blocks till the Ways.Iter() finishes
 		osmCache.Ways.Close()
@@ -183,6 +185,7 @@ func Import() {
 		nodeWriter := writer.NewNodeWriter(osmCache, nodes, db,
 			progress, config.BaseOptions.Srid)
 		nodeWriter.SetLimiter(geometryLimiter)
+		nodeWriter.EnableConcurrent()
 		nodeWriter.Start()
 		nodeWriter.Wait() // blocks till the Nodes.Iter() finishes
 		osmCache.Close()

writer/writer.go

@@ -28,14 +28,23 @@ type OsmElemWriter struct {
 	writer      looper
 	srid        int
 	expireTiles *expire.Tiles
+	concurrent  bool
 }
 
 func (writer *OsmElemWriter) SetLimiter(limiter *limit.Limiter) {
 	writer.limiter = limiter
 }
 
+func (writer *OsmElemWriter) EnableConcurrent() {
+	writer.concurrent = true
+}
+
 func (writer *OsmElemWriter) Start() {
-	for i := 0; i < runtime.NumCPU(); i++ {
+	concurrency := 1
+	if writer.concurrent {
+		concurrency = runtime.NumCPU()
+	}
+	for i := 0; i < concurrency; i++ {
 		writer.wg.Add(1)
 		go writer.writer.loop()
 	}