refactor index manager service

Signed-off-by: kpango <kpango@vdaas.org>

internal/timeutil/time_test.go

@@ -80,6 +80,12 @@ func TestParse(t *testing.T) {
 			want:    0,
 			wantErr: true,
 		},
+		{
+			name:    "returns 0 and incorrect string error when t is minus value",
+			t:       "-1",
+			want:    0,
+			wantErr: true,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

pkg/manager/index/service/indexer.go

@@ -121,23 +121,29 @@ func (idx *index) Start(ctx context.Context) (<-chan error, error) {
 				ech <- err
 			case err = <-sech:
 				ech <- err
-			case <-it.C:
+			case <-it.C: // index duration ticker
+				// execute CreateIndex. This execution ignores low index agent,
+				// and does not immediately execute SaveIndex.
 				err = idx.execute(grpc.WithGRPCMethod(ctx, "core.v1.Agent/CreateIndex"), true, false)
 				if err != nil {
 					ech <- err
 					log.Error("an error occurred during indexing", err)
 					err = nil
 				}
 				it.Reset(idx.indexDuration)
-			case <-itl.C:
+			case <-itl.C: // index duration limit ticker
+				// execute CreateIndex. This execution always executes CreateIndex regardless of the state of the uncommitted index,
+				// but does not immediately execute SaveIndex.
 				err = idx.execute(grpc.WithGRPCMethod(ctx, "core.v1.Agent/CreateIndex"), false, false)
 				if err != nil {
 					ech <- err
 					log.Error("an error occurred during indexing", err)
 					err = nil
 				}
 				itl.Reset(idx.indexDurationLimit)
-			case <-stl.C:
+			case <-stl.C: // save index duration limit ticker
+				// execute CreateIndex. This execution always executes CreateIndex regardless of the state of the uncommitted index,
+				// and immediately execute SaveIndex using CreateAndSaveIndex operation.
 				err = idx.execute(grpc.WithGRPCMethod(ctx, "core.v1.Agent/CreateAndSaveIndex"), false, true)
 				if err != nil {
 					ech <- err
@@ -162,12 +168,12 @@ func (idx *index) Start(ctx context.Context) (<-chan error, error) {
 			select {
 			case <-ctx.Done():
 				return
-			case addr := <-idx.saveIndexTargetAddrCh:
-				idx.schMap.Delete(addr)
+			case addr := <-idx.saveIndexTargetAddrCh: // this channel value send from execute func after thier CreateIndex operation when argument immediateSaving=false.
 				_, err := idx.client.GetClient().
 					Do(grpc.WithGRPCMethod(ctx, "core.v1.Agent/SaveIndex"), addr, func(ctx context.Context, conn *grpc.ClientConn, copts ...grpc.CallOption) (interface{}, error) {
 						return agent.NewAgentClient(conn).SaveIndex(ctx, &payload.Empty{}, copts...)
 					})
+				idx.schMap.Delete(addr) // unlock duplicate signal sending.
 				if err != nil {
 					log.Warnf("an error occurred while calling SaveIndex of %s: %s", addr, err)
 					select {
@@ -198,7 +204,7 @@ func (idx *index) execute(ctx context.Context, enableLowIndexSkip, immediateSavi
 	idx.indexing.Store(true)
 	defer idx.indexing.Store(false)
 	addrs := idx.client.GetAddrs(ctx)
-	err = idx.client.GetClient().OrderedRangeConcurrent(ctx, addrs,
+	return errors.Join(idx.client.GetClient().OrderedRangeConcurrent(ctx, addrs,
 		idx.concurrency,
 		func(ctx context.Context,
 			addr string, conn *grpc.ClientConn, copts ...grpc.CallOption,
@@ -227,7 +233,7 @@ func (idx *index) execute(ctx context.Context, enableLowIndexSkip, immediateSavi
 					log.Warnf("an error occurred while calling CreateIndex of %s: %s", addr, err)
 					return err
 				}
-				_, ok := idx.schMap.Load(addr)
+				_, ok := idx.schMap.Load(addr) // prevent duplicate save index signal.
 				if !ok {
 					select {
 					case <-ctx.Done():
@@ -249,11 +255,7 @@ func (idx *index) execute(ctx context.Context, enableLowIndexSkip, immediateSavi
 			}
 			idx.waitForNextSaving(ctx)
 			return nil
-		})
-	if err != nil {
-		return err
-	}
-	return idx.loadInfos(ctx)
+		}), idx.loadInfos(ctx))
 }
 
 func (idx *index) waitForNextSaving(ctx context.Context) {