MM-45956: Optimize FileInfo stats query (#22603)

* MM-45956: Optimize FileInfo stats query

We Denormalize Post.ChannelId on FileInfo.ChannelId

```release-note
The file info stats query is now optimized by denormalizing the channelID column into the table itself. This will speed up the query to get the file count for a channel on clicking the RHS.

Migration times:
On a MySQL 8.0.31 DB with
1405 rows in FileInfo and 11M posts, it took around 0.3s

On a Postgres 12.14 DB with
1731 rows in FileInfo and 11M posts, it took around 0.27s
```

https://mattermost.atlassian.net/browse/MM-45956

server/channels/store/sqlstore/channel_store.go

@@ -2265,7 +2265,7 @@ func (s SqlChannelStore) GetFileCount(channelId string) (int64, error) {
 		    FileInfo
 		WHERE
 		    FileInfo.DeleteAt = 0
-            AND FileInfo.PostId IN (SELECT id FROM Posts WHERE ChannelId = ?)`,
+            AND FileInfo.ChannelId = ?`,
 		channelId)
 	if err != nil {
 		return 0, errors.Wrapf(err, "failed to count files with channelId=%s", channelId)

server/channels/store/sqlstore/file_info_store.go

@@ -88,6 +88,7 @@ func newSqlFileInfoStore(sqlStore *SqlStore, metrics einterfaces.MetricsInterfac
 		"FileInfo.Id",
 		"FileInfo.CreatorId",
 		"FileInfo.PostId",
+		"COALESCE(FileInfo.ChannelId, '') AS ChannelId",
 		"FileInfo.CreateAt",
 		"FileInfo.UpdateAt",
 		"FileInfo.DeleteAt",
@@ -118,10 +119,10 @@ func (fs SqlFileInfoStore) Save(info *model.FileInfo) (*model.FileInfo, error) {
 
 	query := `
 		INSERT INTO FileInfo
-		(Id, CreatorId, PostId, CreateAt, UpdateAt, DeleteAt, Path, ThumbnailPath, PreviewPath,
+		(Id, CreatorId, PostId, ChannelId, CreateAt, UpdateAt, DeleteAt, Path, ThumbnailPath, PreviewPath,
 			Name, Extension, Size, MimeType, Width, Height, HasPreviewImage, MiniPreview, Content, RemoteId)
 		VALUES
-		(:Id, :CreatorId, :PostId, :CreateAt, :UpdateAt, :DeleteAt, :Path, :ThumbnailPath, :PreviewPath,
+		(:Id, :CreatorId, :PostId, :ChannelId, :CreateAt, :UpdateAt, :DeleteAt, :Path, :ThumbnailPath, :PreviewPath,
 			:Name, :Extension, :Size, :MimeType, :Width, :Height, :HasPreviewImage, :MiniPreview, :Content, :RemoteId)
 	`
 
@@ -133,9 +134,8 @@ func (fs SqlFileInfoStore) Save(info *model.FileInfo) (*model.FileInfo, error) {
 
 func (fs SqlFileInfoStore) GetByIds(ids []string) ([]*model.FileInfo, error) {
 	query := fs.getQueryBuilder().
-		Select(append(fs.queryFields, "COALESCE(P.ChannelId, '') as ChannelId")...).
+		Select(fs.queryFields...).
 		From("FileInfo").
-		LeftJoin("Posts as P ON FileInfo.PostId=P.Id").
 		Where(sq.Eq{"FileInfo.Id": ids}).
 		Where(sq.Eq{"FileInfo.DeleteAt": 0}).
 		OrderBy("FileInfo.CreateAt DESC")
@@ -166,6 +166,8 @@ func (fs SqlFileInfoStore) Upsert(info *model.FileInfo) (*model.FileInfo, error)
 		return nil, err
 	}
 
+	// PostID and ChannelID are deliberately ignored
+	// from the list of fields to keep those two immutable.
 	queryString, args, err := fs.getQueryBuilder().
 		Update("FileInfo").
 		SetMap(map[string]any{
@@ -261,8 +263,7 @@ func (fs SqlFileInfoStore) GetWithOptions(page, perPage int, opt *model.GetFileI
 		From("FileInfo")
 
 	if len(opt.ChannelIds) > 0 {
-		query = query.Join("Posts ON FileInfo.PostId = Posts.Id").
-			Where(sq.Eq{"Posts.ChannelId": opt.ChannelIds})
+		query = query.Where(sq.Eq{"FileInfo.ChannelId": opt.ChannelIds})
 	}
 
 	if len(opt.UserIds) > 0 {
@@ -388,10 +389,11 @@ func (fs SqlFileInfoStore) GetForUser(userId string) ([]*model.FileInfo, error)
 	return infos, nil
 }
 
-func (fs SqlFileInfoStore) AttachToPost(fileId, postId, creatorId string) error {
+func (fs SqlFileInfoStore) AttachToPost(fileId, postId, channelId, creatorId string) error {
 	query := fs.getQueryBuilder().
 		Update("FileInfo").
 		Set("PostId", postId).
+		Set("ChannelId", channelId).
 		Where(sq.And{
 			sq.Eq{"Id": fileId},
 			sq.Eq{"PostId": ""},
@@ -506,10 +508,9 @@ func (fs SqlFileInfoStore) Search(paramsList []*model.SearchParams, userId, team
 		return nil, err
 	}
 	query := fs.getQueryBuilder().
-		Select(append(fs.queryFields, "Coalesce(P.ChannelId, '') AS ChannelId")...).
+		Select(fs.queryFields...).
 		From("FileInfo").
-		LeftJoin("Posts as P ON FileInfo.PostId=P.Id").
-		LeftJoin("Channels as C ON C.Id=P.ChannelId").
+		LeftJoin("Channels as C ON C.Id=FileInfo.ChannelId").
 		LeftJoin("ChannelMembers as CM ON C.Id=CM.ChannelId").
 		Where(sq.Eq{"FileInfo.DeleteAt": 0}).
 		OrderBy("FileInfo.CreateAt DESC").
@@ -715,9 +716,8 @@ func (fs SqlFileInfoStore) CountAll() (int64, error) {
 func (fs SqlFileInfoStore) GetFilesBatchForIndexing(startTime int64, startFileID string, limit int) ([]*model.FileForIndexing, error) {
 	files := []*model.FileForIndexing{}
 	sql, args, _ := fs.getQueryBuilder().
-		Select(append(fs.queryFields, "Coalesce(p.ChannelId, '') AS ChannelId")...).
+		Select(fs.queryFields...).
 		From("FileInfo").
-		LeftJoin("Posts AS p ON FileInfo.PostId = p.Id").
 		Where(sq.Or{
 			sq.Gt{"FileInfo.CreateAt": startTime},
 			sq.And{

server/channels/store/sqlstore/integrity.go

@@ -134,6 +134,15 @@ func checkChannelsPostsIntegrity(ss *SqlStore) model.IntegrityCheckResult {
 	})
 }
 
+func checkChannelsFileInfoIntegrity(ss *SqlStore) model.IntegrityCheckResult {
+	return checkParentChildIntegrity(ss, relationalCheckConfig{
+		parentName:   "Channels",
+		parentIdAttr: "ChannelId",
+		childName:    "FileInfo",
+		childIdAttr:  "Id",
+	})
+}
+
 func checkCommandsCommandWebhooksIntegrity(ss *SqlStore) model.IntegrityCheckResult {
 	return checkParentChildIntegrity(ss, relationalCheckConfig{
 		parentName:   "Commands",
@@ -458,6 +467,7 @@ func checkChannelsIntegrity(ss *SqlStore, results chan<- model.IntegrityCheckRes
 	results <- checkChannelsIncomingWebhooksIntegrity(ss)
 	results <- checkChannelsOutgoingWebhooksIntegrity(ss)
 	results <- checkChannelsPostsIntegrity(ss)
+	results <- checkChannelsFileInfoIntegrity(ss)
 }
 
 func checkCommandsIntegrity(ss *SqlStore, results chan<- model.IntegrityCheckResult) {

server/channels/store/sqlstore/integrity_test.go

@@ -115,7 +115,7 @@ func createEmoji(ss store.Store, userId string) *model.Emoji {
 	return emoji
 }
 
-func createFileInfo(ss store.Store, postId, userId string) *model.FileInfo {
+func createFileInfo(ss store.Store, postId, channelId, userId string) *model.FileInfo {
 	m := model.FileInfo{}
 	m.PostId = postId
 	m.CreatorId = userId
@@ -623,7 +623,7 @@ func TestCheckPostsFileInfoIntegrity(t *testing.T) {
 
 		t.Run("should generate a report with one record", func(t *testing.T) {
 			postId := model.NewId()
-			info := createFileInfo(ss, postId, model.NewId())
+			info := createFileInfo(ss, postId, model.NewId(), model.NewId())
 			result := checkPostsFileInfoIntegrity(store)
 			require.NoError(t, result.Err)
 			data := result.Data.(model.RelationalIntegrityCheckData)
@@ -1226,7 +1226,7 @@ func TestCheckUsersFileInfoIntegrity(t *testing.T) {
 		t.Run("should generate a report with one record", func(t *testing.T) {
 			user := createUser(ss)
 			userId := user.Id
-			info := createFileInfo(ss, model.NewId(), userId)
+			info := createFileInfo(ss, model.NewId(), model.NewId(), userId)
 			dbmap.Exec(`DELETE FROM Users WHERE Id=?`, user.Id)
 			result := checkUsersFileInfoIntegrity(store)
 			require.NoError(t, result.Err)