run building files in background after node startup (#13682)

Closes #13360.

erigon-lib/state/aggregator.go

@@ -667,11 +667,7 @@ func (a *Aggregator) BuildFiles2(ctx context.Context, fromStep, toStep uint64) e
 			}
 		}
 
-		if ok := a.mergingFiles.CompareAndSwap(false, true); !ok {
-			return
-		}
 		go func() {
-			defer a.mergingFiles.Store(false)
 			if err := a.MergeLoop(ctx); err != nil {
 				panic(err)
 			}
@@ -724,7 +720,16 @@ func (a *Aggregator) mergeLoopStep(ctx context.Context, toTxNum uint64) (somethi
 	return true, nil
 }
 
+// TODO: merge must have own semphore
 func (a *Aggregator) MergeLoop(ctx context.Context) error {
+	if dbg.NoMerge() || !a.mergingFiles.CompareAndSwap(false, true) {
+		return nil // currently merging or merge is prohibited
+	}
+
+	a.wg.Add(1)
+	defer a.wg.Done()
+	defer a.mergingFiles.Store(false)
+
 	for {
 		somethingMerged, err := a.mergeLoopStep(ctx, a.visibleFilesMinimaxTxNum.Load())
 		if err != nil {
@@ -1489,6 +1494,7 @@ func (a *Aggregator) BuildFilesInBackground(txNum uint64) chan struct{} {
 			//we are inside own goroutine - it's fine to block here
 			if err := a.snapshotBuildSema.Acquire(a.ctx, 1); err != nil {
 				a.logger.Warn("[snapshots] buildFilesInBackground", "err", err)
+				close(fin)
 				return //nolint
 			}
 			defer a.snapshotBuildSema.Release(1)
@@ -1523,23 +1529,9 @@ func (a *Aggregator) BuildFilesInBackground(txNum uint64) chan struct{} {
 				break
 			}
 		}
-
-		if dbg.NoMerge() {
-			close(fin)
-			return
-		}
-		if ok := a.mergingFiles.CompareAndSwap(false, true); !ok {
-			close(fin)
-			return
-		}
-		a.wg.Add(1)
 		go func() {
-			defer a.wg.Done()
-			defer a.mergingFiles.Store(false)
-
-			//TODO: merge must have own semphore
+			defer close(fin)
 
-			defer func() { close(fin) }()
 			if err := a.MergeLoop(a.ctx); err != nil {
 				if errors.Is(err, context.Canceled) || errors.Is(err, common2.ErrStopped) {
 					return

eth/backend.go

@@ -346,7 +346,6 @@ func New(ctx context.Context, stack *node.Node, config *ethconfig.Config, logger
 	if err != nil {
 		return nil, err
 	}
-
 	backend.blockSnapshots, backend.blockReader, backend.blockWriter = allSnapshots, blockReader, blockWriter
 
 	backend.chainDB, err = temporal.New(rawChainDB, agg)
@@ -1086,6 +1085,12 @@ func New(ctx context.Context, stack *node.Node, config *ethconfig.Config, logger
 		}
 	}
 
+	go func() {
+		if err := agg.MergeLoop(ctx); err != nil {
+			logger.Error("snapashot merge loop error", "err", err)
+		}
+	}()
+
 	return backend, nil
 }