Add snapshot-disable-gc flag (#874)

GC defects are found for sequence data types such as Array, Text, and
Tree. This commit provides the option to temporarily turn off GC on
the server.

cmd/yorkie/server.go

@@ -291,6 +291,12 @@ func init() {
 		server.DefaultSnapshotWithPurgingChanges,
 		"Whether to delete previous changes when the snapshot is created.",
 	)
+	cmd.Flags().BoolVar(
+		&conf.Backend.SnapshotDisableGC,
+		"backend-snapshot-disable-gc",
+		server.DefaultSnapshotDisableGC,
+		"Whether to disable garbage collection of snapshots.",
+	)
 	cmd.Flags().Uint64Var(
 		&conf.Backend.AuthWebhookMaxRetries,
 		"auth-webhook-max-retries",

pkg/document/document.go

@@ -65,6 +65,22 @@ type BroadcastRequest struct {
 	Payload []byte
 }
 
+// Option configures Options.
+type Option func(*Options)
+
+// Options configures how we set up the document.
+type Options struct {
+	// DisableGC disables garbage collection.
+	DisableGC bool
+}
+
+// WithDisableGC configures the document to disable garbage collection.
+func WithDisableGC() Option {
+	return func(o *Options) {
+		o.DisableGC = true
+	}
+}
+
 // Document represents a document accessible to the user.
 //
 // How document works:
@@ -76,6 +92,9 @@ type Document struct {
 	// doc is the original data of the actual document.
 	doc *InternalDocument
 
+	// options is the options to configure the document.
+	options Options
+
 	// cloneRoot is a copy of `doc.root` to be exposed to the user and is used to
 	// protect `doc.root`.
 	cloneRoot *crdt.Root
@@ -100,9 +119,15 @@ type Document struct {
 }
 
 // New creates a new instance of Document.
-func New(key key.Key) *Document {
+func New(key key.Key, opts ...Option) *Document {
+	var options Options
+	for _, opt := range opts {
+		opt(&options)
+	}
+
 	return &Document{
 		doc:                NewInternalDocument(key),
+		options:            options,
 		events:             make(chan DocEvent, 1),
 		broadcastRequests:  make(chan BroadcastRequest, 1),
 		broadcastResponses: make(chan error, 1),
@@ -197,7 +222,9 @@ func (d *Document) ApplyChangePack(pack *change.Pack) error {
 	d.doc.checkpoint = d.doc.checkpoint.Forward(pack.Checkpoint)
 
 	// 04. Do Garbage collection.
-	d.GarbageCollect(pack.MinSyncedTicket)
+	if !d.options.DisableGC {
+		d.GarbageCollect(pack.MinSyncedTicket)
+	}
 
 	// 05. Update the status.
 	if pack.IsRemoved {

pkg/document/internal_document.go

@@ -142,7 +142,7 @@ func (d *InternalDocument) HasLocalChanges() bool {
 }
 
 // ApplyChangePack applies the given change pack into this document.
-func (d *InternalDocument) ApplyChangePack(pack *change.Pack) error {
+func (d *InternalDocument) ApplyChangePack(pack *change.Pack, disableGC bool) error {
 	// 01. Apply remote changes to both the cloneRoot and the document.
 	if len(pack.Snapshot) > 0 {
 		if err := d.applySnapshot(pack.Snapshot, pack.Checkpoint.ServerSeq); err != nil {
@@ -166,7 +166,7 @@ func (d *InternalDocument) ApplyChangePack(pack *change.Pack) error {
 	// 03. Update the checkpoint.
 	d.checkpoint = d.checkpoint.Forward(pack.Checkpoint)
 
-	if pack.MinSyncedTicket != nil {
+	if !disableGC && pack.MinSyncedTicket != nil {
 		if _, err := d.GarbageCollect(pack.MinSyncedTicket); err != nil {
 			return err
 		}

server/backend/config.go

@@ -55,6 +55,9 @@ type Config struct {
 	// SnapshotWithPurgingChanges is whether to delete previous changes when the snapshot is created.
 	SnapshotWithPurgingChanges bool `yaml:"SnapshotWithPurgingChages"`
 
+	// SnapshotDisableGC is whether to disable garbage collection of snapshots.
+	SnapshotDisableGC bool
+
 	// AuthWebhookMaxRetries is the max count that retries the authorization webhook.
 	AuthWebhookMaxRetries uint64 `yaml:"AuthWebhookMaxRetries"`
 

server/config.go

@@ -58,6 +58,7 @@ const (
 	DefaultSnapshotThreshold          = 500
 	DefaultSnapshotInterval           = 1000
 	DefaultSnapshotWithPurgingChanges = false
+	DefaultSnapshotDisableGC          = false
 
 	DefaultAuthWebhookMaxRetries      = 10
 	DefaultAuthWebhookMaxWaitInterval = 3000 * time.Millisecond

server/packs/packs.go

@@ -236,7 +236,7 @@ func BuildDocumentForServerSeq(
 		change.InitialCheckpoint.NextServerSeq(serverSeq),
 		changes,
 		nil,
-	)); err != nil {
+	), be.Config.SnapshotDisableGC); err != nil {
 		return nil, err
 	}
 

server/packs/pushpull.go

@@ -151,7 +151,7 @@ func pullSnapshot(
 			doc.Checkpoint().NextServerSeq(docInfo.ServerSeq),
 			reqPack.Changes,
 			nil,
-		)); err != nil {
+		), be.Config.SnapshotDisableGC); err != nil {
 			return nil, err
 		}
 	}

server/packs/snapshots.go

@@ -91,7 +91,7 @@ func storeSnapshot(
 	)
 	pack.MinSyncedTicket = minSyncedTicket
 
-	if err := doc.ApplyChangePack(pack); err != nil {
+	if err := doc.ApplyChangePack(pack, be.Config.SnapshotDisableGC); err != nil {
 		return err
 	}
 

test/integration/gc_test.go

@@ -20,14 +20,17 @@ package integration
 
 import (
 	"context"
+	"strconv"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 
+	"github.com/yorkie-team/yorkie/client"
 	"github.com/yorkie-team/yorkie/pkg/document"
 	"github.com/yorkie-team/yorkie/pkg/document/json"
 	"github.com/yorkie-team/yorkie/pkg/document/presence"
 	"github.com/yorkie-team/yorkie/pkg/document/time"
+	"github.com/yorkie-team/yorkie/server"
 	"github.com/yorkie-team/yorkie/test/helper"
 )
 
@@ -602,4 +605,63 @@ func TestGarbageCollection(t *testing.T) {
 		assert.Equal(t, `<r>ad</r>`, d2.Root().GetTree("tree").ToXML())
 		assert.Equal(t, 0, d1.GarbageLen())
 	})
+
+	t.Run("Should not collect the garbage if the DisableGC is true", func(t *testing.T) {
+		// 01. Create a new server with SnapshotDisableGC set to true
+		conf := helper.TestConfig()
+		conf.Backend.SnapshotDisableGC = true
+		conf.Backend.SnapshotThreshold = 10
+		conf.Backend.SnapshotInterval = 10
+		testServer, err := server.New(conf)
+		assert.NoError(t, err)
+		assert.NoError(t, testServer.Start())
+		defer func() {
+			assert.NoError(t, testServer.Shutdown(true))
+		}()
+
+		ctx := context.Background()
+		c1, err := client.Dial(testServer.RPCAddr())
+		assert.NoError(t, err)
+		assert.NoError(t, c1.Activate(ctx))
+		defer func() {
+			assert.NoError(t, c1.Deactivate(ctx))
+			assert.NoError(t, c1.Close())
+		}()
+
+		// 02. Create a document and update it to check if the garbage is collected
+		d1 := document.New(helper.TestDocKey(t), document.WithDisableGC())
+		assert.NoError(t, c1.Attach(ctx, d1))
+		defer func() {
+			assert.NoError(t, c1.Detach(ctx, d1))
+		}()
+
+		assert.NoError(t, d1.Update(func(root *json.Object, p *presence.Presence) error {
+			root.SetNewText("text").Edit(0, 0, "-")
+			return nil
+		}))
+		for i := 0; i < int(conf.Backend.SnapshotInterval); i++ {
+			assert.NoError(t, d1.Update(func(root *json.Object, p *presence.Presence) error {
+				root.GetText("text").Edit(0, 1, strconv.Itoa(i))
+				return nil
+			}))
+		}
+		assert.Equal(t, int(conf.Backend.SnapshotInterval), d1.GarbageLen())
+		assert.NoError(t, c1.Sync(ctx))
+
+		// 03. Check if the garbage is collected after the snapshot interval
+		c2, err := client.Dial(testServer.RPCAddr())
+		assert.NoError(t, err)
+		assert.NoError(t, c2.Activate(ctx))
+		defer func() {
+			assert.NoError(t, c2.Deactivate(ctx))
+			assert.NoError(t, c2.Close())
+		}()
+
+		d2 := document.New(helper.TestDocKey(t), document.WithDisableGC())
+		assert.NoError(t, c2.Attach(ctx, d2))
+		defer func() {
+			assert.NoError(t, c2.Detach(ctx, d2))
+		}()
+		assert.Equal(t, int(conf.Backend.SnapshotInterval), d2.GarbageLen())
+	})
 }