Use buffersize to reduce database connection when iterate (#2724)

* use buffersize to reduce database connection when iterate

* fix typo

* add default value on app.ini comment

conf/app.ini

 PATH = data/gitea.db
 ; For "sqlite3" only. Query timeout
 SQLITE_TIMEOUT = 500
+; For iterate buffer, default is 50
+ITERATE_BUFFER_SIZE = 50
 
 [indexer]
 ISSUE_INDEXER_PATH = indexers/issues.bleve

models/migrations/v19.go

 		}
 	)
 
-	return x.Where("id > 0").Iterate(new(Repository),
+	return x.Where("id > 0").BufferSize(setting.IterateBufferSize).Iterate(new(Repository),
 		func(idx int, bean interface{}) error {
 			repo := bean.(*Repository)
 			user := new(User)

models/migrations/v22.go

 		}
 	)
 
-	return x.Where("id > 0").Iterate(new(Repository),
+	return x.Where("id > 0").BufferSize(setting.IterateBufferSize).Iterate(new(Repository),
 		func(idx int, bean interface{}) error {
 			repo := bean.(*Repository)
 			user := new(User)

models/migrations/v26.go

 		hookTpl   = fmt.Sprintf("#!/usr/bin/env %s\ndata=$(cat)\nexitcodes=\"\"\nhookname=$(basename $0)\nGIT_DIR=${GIT_DIR:-$(dirname $0)}\n\nfor hook in ${GIT_DIR}/hooks/${hookname}.d/*; do\ntest -x \"${hook}\" || continue\necho \"${data}\" | \"${hook}\"\nexitcodes=\"${exitcodes} $?\"\ndone\n\nfor i in ${exitcodes}; do\n[ ${i} -eq 0 ] || exit ${i}\ndone\n", setting.ScriptType)
 	)
 
-	return x.Where("id > 0").Iterate(new(Repository),
+	return x.Where("id > 0").BufferSize(setting.IterateBufferSize).Iterate(new(Repository),
 		func(idx int, bean interface{}) error {
 			repo := bean.(*Repository)
 			user := new(User)

models/repo.go

 	log.Trace("Doing: GitFsck")
 
 	if err := x.
-		Where("id>0").
+		Where("id>0").BufferSize(setting.IterateBufferSize).
 		Iterate(new(Repository),
 			func(idx int, bean interface{}) error {
 				repo := bean.(*Repository)
 func GitGcRepos() error {
 	args := append([]string{"gc"}, setting.Git.GCArgs...)
 	return x.
-		Where("id > 0").
+		Where("id > 0").BufferSize(setting.IterateBufferSize).
 		Iterate(new(Repository),
 			func(idx int, bean interface{}) error {
 				repo := bean.(*Repository)

models/user.go

 	}
 
 	// Delete all local copies of repository wiki that user owns.
-	if err = x.
+	if err = x.BufferSize(setting.IterateBufferSize).
 		Where("owner_id=?", u.ID).
 		Iterate(new(Repository), func(idx int, bean interface{}) error {
 			repo := bean.(*Repository)

modules/setting/setting.go

 	ShowFooterTemplateLoadTime bool
 
 	// Global setting objects
-	Cfg           *ini.File
-	CustomPath    string // Custom directory path
-	CustomConf    string
-	CustomPID     string
-	ProdMode      bool
-	RunUser       string
-	IsWindows     bool
-	HasRobotsTxt  bool
-	InternalToken string // internal access token
+	Cfg               *ini.File
+	CustomPath        string // Custom directory path
+	CustomConf        string
+	CustomPID         string
+	ProdMode          bool
+	RunUser           string
+	IsWindows         bool
+	HasRobotsTxt      bool
+	InternalToken     string // internal access token
+	IterateBufferSize int
 )
 
 // DateLang transforms standard language locale name to corresponding value in datetime plugin.
 			log.Fatal(4, "Error saving generated JWT Secret to custom config: %v", err)
 		}
 	}
+	IterateBufferSize = Cfg.Section("database").Key("ITERATE_BUFFER_SIZE").MustInt(50)
 
 	sec = Cfg.Section("attachment")
 	AttachmentPath = sec.Key("PATH").MustString(path.Join(AppDataPath, "attachments"))