{"record":{"id":"30287455e6530af9","repo":"cloudreve/cloudreve","slug":"failed-to-start-transaction-w-302874","errorCode":null,"errorMessage":"failed to start transaction: %w","messagePattern":"failed to start transaction: %w","errorType":"console","errorClass":null,"httpStatus":null,"severity":"error","filePath":"application/migrator/user.go","lineNumber":45,"sourceCode":"\tfor {\n\t\tm.l.Info(\"Migrating users with offset %d\", offset)\n\t\tvar users []model.User\n\t\tif err := model.DB.Limit(batchSize).Offset(offset).Find(&users).Error; err != nil {\n\t\t\treturn fmt.Errorf(\"failed to list v3 users: %w\", err)\n\t\t}\n\n\t\tif len(users) == 0 {\n\t\t\tif m.dep.ConfigProvider().Database().Type == conf.PostgresDB {\n\t\t\t\tm.l.Info(\"Resetting user ID sequence for postgres...\")\n\t\t\t\tm.v4client.User.ExecContext(ctx, \"SELECT SETVAL('users_id_seq',  (SELECT MAX(id) FROM users))\")\n\t\t\t}\n\t\t\tbreak\n\t\t}\n\n\t\ttx, err := m.v4client.Tx(context.Background())\n\t\tif err != nil {\n\t\t\t_ = tx.Rollback()\n\t\t\treturn fmt.Errorf(\"failed to start transaction: %w\", err)\n\t\t}\n\n\t\tfor _, u := range users {\n\t\t\tuserStatus := user.StatusActive\n\t\t\tswitch u.Status {\n\t\t\tcase model.Active:\n\t\t\t\tuserStatus = user.StatusActive\n\t\t\tcase model.NotActivicated:\n\t\t\t\tuserStatus = user.StatusInactive\n\t\t\tcase model.Baned:\n\t\t\t\tuserStatus = user.StatusManualBanned\n\t\t\tcase model.OveruseBaned:\n\t\t\t\tuserStatus = user.StatusSysBanned\n\t\t\t}\n\n\t\t\tsetting := &types.UserSetting{\n\t\t\t\tVersionRetention:    true,\n\t\t\t\tVersionRetentionMax: 10,","sourceCodeStart":27,"sourceCodeEnd":63,"githubUrl":"https://github.com/cloudreve/cloudreve/blob/20c95ad73f3a8bcb72887fea91ff31ab24fa1011/application/migrator/user.go#L27-L63","documentation":"Returned when m.v4client.Tx(context.Background()) fails to open the batch transaction on the v4 target (application/migrator/user.go:44-47). ent returns a nil *Tx with the error; as with the share migrator, the following _ = tx.Rollback() runs on that nil Tx and ent's Tx.Rollback dereferences tx.config (ent/tx.go:148-149), so this path usually surfaces as a nil-pointer panic rather than the wrapped 'failed to start transaction' error.","triggerScenarios":"v4 DB down/unreachable; too many connections; missing transaction privilege; connect timeout from an exhausted pool; context canceled by an upstream shutdown.","commonSituations":"Starting user migration before the v4 database is ready; DB connection limits consumed by the app plus migration; wrong v4 DSN passed to the migrator; Kubernetes pod DNS not resolving the DB service.","solutions":["If you got a panic instead of this error string, the nil tx.Rollback() is the cause - resolve the underlying connection failure.","Confirm v4 connectivity/credentials from the migration host.","Free up connection slots (stop the v4 instance during migration) or raise max_connections.","Patch out the _ = tx.Rollback() line so future failures return the real error."],"exampleFix":"// before\ntx, err := m.v4client.Tx(context.Background())\nif err != nil {\n\t_ = tx.Rollback() // tx is nil -> panic\n\treturn fmt.Errorf(\"failed to start transaction: %w\", err)\n}\n\n// after\ntx, err := m.v4client.Tx(context.Background())\nif err != nil {\n\treturn fmt.Errorf(\"failed to start transaction: %w\", err)\n}","handlingStrategy":"validation","validationCode":"// Round-trip test before the loop\ntx, err := v4client.Tx(context.Background())\nif err != nil {\n\treturn fmt.Errorf(\"v4 DB cannot open transaction: %w\", err)\n}\n_ = tx.Rollback()","typeGuard":"if tx == nil && err != nil {\n\t// ent failed to create the Tx; touching tx.Rollback() panics\n\treturn err\n}","tryCatchPattern":"tx, err := m.v4client.Tx(context.Background())\nif err != nil {\n\t// no Rollback call: tx is nil here\n\treturn fmt.Errorf(\"failed to start transaction: %w\", err)\n}","preventionTips":["Fix the nil-Rollback pattern in custom migrators: only Rollback a successfully created Tx.","Ensure the v4 DB is up and connection headroom exists before user batches begin.","Pre-flight a Tx/Rollback pair to surface connectivity issues early."],"tags":["go","cloudreve","migration","ent","transaction","nil-pointer","database"],"backgroundTag":null,"analyzedSha":"20c95ad73f3a8bcb72887fea91ff31ab24fa1011","analyzedAt":"2026-08-16T01:42:55.403Z","schemaVersion":2},"datasetVersion":"2026-08-16T03:17:38.424Z"}