diff --git a/database/gdb/gdb.go b/database/gdb/gdb.go
index 10672ca3a..6a3772397 100644
--- a/database/gdb/gdb.go
+++ b/database/gdb/gdb.go
@@ -35,6 +35,7 @@ type DB interface {
 	// The DB interface is designed not only for
 	// relational databases but also for NoSQL databases in the future. The name
 	// "Table" is not proper for that purpose any more.
+	// Also see  Core.Table.
 	// Deprecated, use Model instead.
 	Table(table ...string) *Model
 
@@ -46,144 +47,151 @@ type DB interface {
 	//    Model("user, user_detail")
 	//    Model("user u, user_detail ud")
 	// 2. Model name with alias: Model("user", "u")
+	// Also see Core.Model.
 	Model(table ...string) *Model
 
 	// Schema creates and returns a schema.
+	// Also see Core.Schema.
 	Schema(schema string) *Schema
 
 	// With creates and returns an ORM model based on meta data of given object.
+	// Also see Core.With.
 	With(object interface{}) *Model
 
 	// Open creates a raw connection object for database with given node configuration.
 	// Note that it is not recommended using the this function manually.
+	// Also see DriverMysql.Open.
 	Open(config *ConfigNode) (*sql.DB, error)
 
 	// Ctx is a chaining function, which creates and returns a new DB that is a shallow copy
 	// of current DB object and with given context in it.
 	// Note that this returned DB object can be used only once, so do not assign it to
 	// a global or package variable for long using.
+	// Also see Core.Ctx.
 	Ctx(ctx context.Context) DB
 
 	// ===========================================================================
 	// Query APIs.
 	// ===========================================================================
 
-	Query(sql string, args ...interface{}) (*sql.Rows, error)
-	Exec(sql string, args ...interface{}) (sql.Result, error)
-	Prepare(sql string, execOnMaster ...bool) (*Stmt, error)
+	Query(sql string, args ...interface{}) (*sql.Rows, error) // See Core.Query.
+	Exec(sql string, args ...interface{}) (sql.Result, error) // See Core.Exec.
+	Prepare(sql string, execOnMaster ...bool) (*Stmt, error)  // See Core.Prepare.
 
 	// ===========================================================================
 	// Common APIs for CURD.
 	// ===========================================================================
 
-	Insert(table string, data interface{}, batch ...int) (sql.Result, error)
-	InsertIgnore(table string, data interface{}, batch ...int) (sql.Result, error)
-	Replace(table string, data interface{}, batch ...int) (sql.Result, error)
-	Save(table string, data interface{}, batch ...int) (sql.Result, error)
+	Insert(table string, data interface{}, batch ...int) (sql.Result, error)       // See Core.Insert.
+	InsertIgnore(table string, data interface{}, batch ...int) (sql.Result, error) // See Core.InsertIgnore.
+	Replace(table string, data interface{}, batch ...int) (sql.Result, error)      // See Core.Replace.
+	Save(table string, data interface{}, batch ...int) (sql.Result, error)         // See Core.Save.
 
-	BatchInsert(table string, list interface{}, batch ...int) (sql.Result, error)
-	BatchReplace(table string, list interface{}, batch ...int) (sql.Result, error)
-	BatchSave(table string, list interface{}, batch ...int) (sql.Result, error)
+	BatchInsert(table string, list interface{}, batch ...int) (sql.Result, error)  // See Core.BatchInsert.
+	BatchReplace(table string, list interface{}, batch ...int) (sql.Result, error) // See Core.BatchReplace.
+	BatchSave(table string, list interface{}, batch ...int) (sql.Result, error)    // See Core.BatchSave.
 
-	Update(table string, data interface{}, condition interface{}, args ...interface{}) (sql.Result, error)
-	Delete(table string, condition interface{}, args ...interface{}) (sql.Result, error)
+	Update(table string, data interface{}, condition interface{}, args ...interface{}) (sql.Result, error) // See Core.Update.
+	Delete(table string, condition interface{}, args ...interface{}) (sql.Result, error)                   // See Core.Delete.
 
 	// ===========================================================================
 	// Internal APIs for CURD, which can be overwrote for custom CURD implements.
 	// ===========================================================================
 
-	DoQuery(link Link, sql string, args ...interface{}) (rows *sql.Rows, err error)
-	DoGetAll(link Link, sql string, args ...interface{}) (result Result, err error)
-	DoExec(link Link, sql string, args ...interface{}) (result sql.Result, err error)
-	DoPrepare(link Link, sql string) (*Stmt, error)
-	DoInsert(link Link, table string, data interface{}, option int, batch ...int) (result sql.Result, err error)
-	DoBatchInsert(link Link, table string, list interface{}, option int, batch ...int) (result sql.Result, err error)
-	DoUpdate(link Link, table string, data interface{}, condition string, args ...interface{}) (result sql.Result, err error)
-	DoDelete(link Link, table string, condition string, args ...interface{}) (result sql.Result, err error)
+	DoQuery(link Link, sql string, args ...interface{}) (rows *sql.Rows, err error)                                           // See Core.DoQuery.
+	DoGetAll(link Link, sql string, args ...interface{}) (result Result, err error)                                           // See Core.DoGetAll.
+	DoExec(link Link, sql string, args ...interface{}) (result sql.Result, err error)                                         // See Core.DoExec.
+	DoPrepare(link Link, sql string) (*Stmt, error)                                                                           // See Core.DoPrepare.
+	DoInsert(link Link, table string, data interface{}, option int, batch ...int) (result sql.Result, err error)              // See Core.DoInsert.
+	DoBatchInsert(link Link, table string, list interface{}, option int, batch ...int) (result sql.Result, err error)         // See Core.DoBatchInsert.
+	DoUpdate(link Link, table string, data interface{}, condition string, args ...interface{}) (result sql.Result, err error) // See Core.DoUpdate.
+	DoDelete(link Link, table string, condition string, args ...interface{}) (result sql.Result, err error)                   // See Core.DoDelete.
 
 	// ===========================================================================
 	// Query APIs for convenience purpose.
 	// ===========================================================================
 
-	GetAll(sql string, args ...interface{}) (Result, error)
-	GetOne(sql string, args ...interface{}) (Record, error)
-	GetValue(sql string, args ...interface{}) (Value, error)
-	GetArray(sql string, args ...interface{}) ([]Value, error)
-	GetCount(sql string, args ...interface{}) (int, error)
-	GetStruct(objPointer interface{}, sql string, args ...interface{}) error
-	GetStructs(objPointerSlice interface{}, sql string, args ...interface{}) error
-	GetScan(objPointer interface{}, sql string, args ...interface{}) error
+	GetAll(sql string, args ...interface{}) (Result, error)                        // See Core.GetAll.
+	GetOne(sql string, args ...interface{}) (Record, error)                        // See Core.GetOne.
+	GetValue(sql string, args ...interface{}) (Value, error)                       // See Core.GetValue.
+	GetArray(sql string, args ...interface{}) ([]Value, error)                     // See Core.GetArray.
+	GetCount(sql string, args ...interface{}) (int, error)                         // See Core.GetCount.
+	GetStruct(objPointer interface{}, sql string, args ...interface{}) error       // See Core.GetStruct.
+	GetStructs(objPointerSlice interface{}, sql string, args ...interface{}) error // See Core.GetStructs.
+	GetScan(objPointer interface{}, sql string, args ...interface{}) error         // See Core.GetScan.
 
 	// ===========================================================================
 	// Master/Slave specification support.
 	// ===========================================================================
 
-	Master() (*sql.DB, error)
-	Slave() (*sql.DB, error)
+	Master() (*sql.DB, error) // See Core.Master.
+	Slave() (*sql.DB, error)  // See Core.Slave.
 
 	// ===========================================================================
 	// Ping-Pong.
 	// ===========================================================================
 
-	PingMaster() error
-	PingSlave() error
+	PingMaster() error // See Core.PingMaster.
+	PingSlave() error  // See Core.PingSlave.
 
 	// ===========================================================================
 	// Transaction.
 	// ===========================================================================
 
-	Begin() (*TX, error)
-	Transaction(f func(tx *TX) error) (err error)
+	Begin() (*TX, error)                          // See Core.Begin.
+	Transaction(f func(tx *TX) error) (err error) // See Core.Transaction.
 
 	// ===========================================================================
 	// Configuration methods.
 	// ===========================================================================
 
-	GetCache() *gcache.Cache
-	SetDebug(debug bool)
-	GetDebug() bool
-	SetSchema(schema string)
-	GetSchema() string
-	GetPrefix() string
-	GetGroup() string
-	SetDryRun(dryrun bool)
-	GetDryRun() bool
-	SetLogger(logger *glog.Logger)
-	GetLogger() *glog.Logger
-	GetConfig() *ConfigNode
-	SetMaxIdleConnCount(n int)
-	SetMaxOpenConnCount(n int)
-	SetMaxConnLifetime(d time.Duration)
+	GetCache() *gcache.Cache            // See Core.GetCache.
+	SetDebug(debug bool)                // See Core.SetDebug.
+	GetDebug() bool                     // See Core.GetDebug.
+	SetSchema(schema string)            // See Core.SetSchema.
+	GetSchema() string                  // See Core.GetSchema.
+	GetPrefix() string                  // See Core.GetPrefix.
+	GetGroup() string                   // See Core.GetGroup.
+	SetDryRun(enabled bool)             // See Core.SetDryRun.
+	GetDryRun() bool                    // See Core.GetDryRun.
+	SetLogger(logger *glog.Logger)      // See Core.SetLogger.
+	GetLogger() *glog.Logger            // See Core.GetLogger.
+	GetConfig() *ConfigNode             // See Core.GetConfig.
+	SetMaxIdleConnCount(n int)          // See Core.SetMaxIdleConnCount.
+	SetMaxOpenConnCount(n int)          // See Core.SetMaxOpenConnCount.
+	SetMaxConnLifeTime(d time.Duration) // See Core.SetMaxConnLifeTime.
+	SetMaxConnIdleTime(d time.Duration) // See Core.SetMaxConnIdleTime
 
 	// ===========================================================================
 	// Utility methods.
 	// ===========================================================================
 
-	GetCtx() context.Context
-	GetChars() (charLeft string, charRight string)
-	GetMaster(schema ...string) (*sql.DB, error)
-	GetSlave(schema ...string) (*sql.DB, error)
-	QuoteWord(s string) string
-	QuoteString(s string) string
-	QuotePrefixTableName(table string) string
-	Tables(schema ...string) (tables []string, err error)
-	TableFields(table string, schema ...string) (map[string]*TableField, error)
-	HasTable(name string) (bool, error)
-	FilteredLinkInfo() string
+	GetCtx() context.Context                                                               // See Core.GetCtx.
+	GetChars() (charLeft string, charRight string)                                         // See Core.GetChars.
+	GetMaster(schema ...string) (*sql.DB, error)                                           // See Core.GetMaster.
+	GetSlave(schema ...string) (*sql.DB, error)                                            // See Core.GetSlave.
+	QuoteWord(s string) string                                                             // See Core.QuoteWord.
+	QuoteString(s string) string                                                           // See Core.QuoteString.
+	QuotePrefixTableName(table string) string                                              // See Core.QuotePrefixTableName.
+	Tables(schema ...string) (tables []string, err error)                                  // See Core.Tables.
+	TableFields(link Link, table string, schema ...string) (map[string]*TableField, error) // See Core.TableFields.
+	HasTable(name string) (bool, error)                                                    // See Core.HasTable.
+	FilteredLinkInfo() string                                                              // See Core.FilteredLinkInfo.
 
 	// HandleSqlBeforeCommit is a hook function, which deals with the sql string before
 	// it's committed to underlying driver. The parameter `link` specifies the current
 	// database connection operation object. You can modify the sql string `sql` and its
 	// arguments `args` as you wish before they're committed to driver.
+	// Also see Core.HandleSqlBeforeCommit.
 	HandleSqlBeforeCommit(link Link, sql string, args []interface{}) (string, []interface{})
 
 	// ===========================================================================
 	// Internal methods, for internal usage purpose, you do not need consider it.
 	// ===========================================================================
 
-	mappingAndFilterData(schema, table string, data map[string]interface{}, filter bool) (map[string]interface{}, error)
-	convertFieldValueToLocalValue(fieldValue interface{}, fieldType string) interface{}
-	convertRowsToResult(rows *sql.Rows) (Result, error)
+	mappingAndFilterData(schema, table string, data map[string]interface{}, filter bool) (map[string]interface{}, error) // See Core.mappingAndFilterData.
+	convertFieldValueToLocalValue(fieldValue interface{}, fieldType string) interface{}                                  // See Core.convertFieldValueToLocalValue.
+	convertRowsToResult(rows *sql.Rows) (Result, error)                                                                  // See Core.convertRowsToResult.
 }
 
 // Core is the base struct for database management.
@@ -299,6 +307,9 @@ var (
 	// internalCache is the memory cache for internal usage.
 	internalCache = gcache.New()
 
+	// tableFieldsMap caches the table information retrived from database.
+	tableFieldsMap = gmap.New(true)
+
 	// allDryRun sets dry-run feature for all database connections.
 	// It is commonly used for command options for convenience.
 	allDryRun = false
@@ -471,15 +482,26 @@ func (c *Core) getSqlDb(master bool, schema ...string) (sqlDb *sql.DB, err error
 	}
 	// Cache the underlying connection pool object by node.
 	v, _ := internalCache.GetOrSetFuncLock(node.String(), func() (interface{}, error) {
-		sqlDb, err = c.db.Open(node)
-		if err != nil {
-			intlog.Printf(`db open failed: %v, %+v`, err, node)
-			return nil, err
-		}
 		intlog.Printf(
-			`open new connection, master:%v, config:%+v, node:%+v`,
+			`open new connection, master:%#v, config:%#v, node:%#v`,
 			master, c.config, node,
 		)
+		defer func() {
+			if err != nil {
+				intlog.Printf(`open new connection failed: %v, %#v`, err, node)
+			} else {
+				intlog.Printf(
+					`open new connection success, master:%#v, config:%#v, node:%#v`,
+					master, c.config, node,
+				)
+			}
+		}()
+
+		sqlDb, err = c.db.Open(node)
+		if err != nil {
+			return nil, err
+		}
+
 		if c.config.MaxIdleConnCount > 0 {
 			sqlDb.SetMaxIdleConns(c.config.MaxIdleConnCount)
 		} else {
@@ -490,17 +512,24 @@ func (c *Core) getSqlDb(master bool, schema ...string) (sqlDb *sql.DB, err error
 		} else {
 			sqlDb.SetMaxOpenConns(defaultMaxOpenConnCount)
 		}
-		if c.config.MaxConnLifetime > 0 {
+		if c.config.MaxConnLifeTime > 0 {
 			// Automatically checks whether MaxConnLifetime is configured using string like: "30s", "60s", etc.
 			// Or else it is configured just using number, which means value in seconds.
-			if c.config.MaxConnLifetime > time.Second {
-				sqlDb.SetConnMaxLifetime(c.config.MaxConnLifetime)
+			if c.config.MaxConnLifeTime > time.Second {
+				sqlDb.SetConnMaxLifetime(c.config.MaxConnLifeTime)
 			} else {
-				sqlDb.SetConnMaxLifetime(c.config.MaxConnLifetime * time.Second)
+				sqlDb.SetConnMaxLifetime(c.config.MaxConnLifeTime * time.Second)
 			}
 		} else {
 			sqlDb.SetConnMaxLifetime(defaultMaxConnLifeTime)
 		}
+		if c.config.MaxConnIdleTime > 0 {
+			if c.config.MaxConnIdleTime > time.Second {
+				sqlDb.SetConnMaxIdleTime(c.config.MaxConnIdleTime)
+			} else {
+				sqlDb.SetConnMaxIdleTime(c.config.MaxConnIdleTime * time.Second)
+			}
+		}
 		return sqlDb, nil
 	}, 0)
 	if v != nil && sqlDb == nil {
diff --git a/database/gdb/gdb_core.go b/database/gdb/gdb_core.go
index 7f2a6a1b5..8265c540a 100644
--- a/database/gdb/gdb_core.go
+++ b/database/gdb/gdb_core.go
@@ -113,7 +113,6 @@ func (c *Core) DoQuery(link Link, sql string, args ...interface{}) (rows *sql.Ro
 	if c.GetConfig().QueryTimeout > 0 {
 		ctx, _ = context.WithTimeout(ctx, c.GetConfig().QueryTimeout)
 	}
-
 	mTime1 := gtime.TimestampMilli()
 	rows, err = link.QueryContext(ctx, sql, args...)
 	mTime2 := gtime.TimestampMilli()
@@ -277,7 +276,7 @@ func (c *Core) GetOne(sql string, args ...interface{}) (Record, error) {
 }
 
 // GetArray queries and returns data values as slice from database.
-// Note that if there're multiple columns in the result, it returns just one column values randomly.
+// Note that if there are multiple columns in the result, it returns just one column values randomly.
 func (c *Core) GetArray(sql string, args ...interface{}) ([]Value, error) {
 	all, err := c.db.DoGetAll(nil, sql, args...)
 	if err != nil {
@@ -382,13 +381,13 @@ func (c *Core) Begin() (*TX, error) {
 	if master, err := c.db.Master(); err != nil {
 		return nil, err
 	} else {
-		ctx := c.db.GetCtx()
-		if c.GetConfig().TranTimeout > 0 {
-			var cancelFunc context.CancelFunc
-			ctx, cancelFunc = context.WithTimeout(ctx, c.GetConfig().TranTimeout)
-			defer cancelFunc()
-		}
-		if tx, err := master.BeginTx(ctx, nil); err == nil {
+		//ctx := c.db.GetCtx()
+		//if c.GetConfig().TranTimeout > 0 {
+		//	var cancelFunc context.CancelFunc
+		//	ctx, cancelFunc = context.WithTimeout(ctx, c.GetConfig().TranTimeout)
+		//	defer cancelFunc()
+		//}
+		if tx, err := master.Begin(); err == nil {
 			return &TX{
 				db:     c.db,
 				tx:     tx,
diff --git a/database/gdb/gdb_core_config.go b/database/gdb/gdb_core_config.go
index ab222cf44..a5df3c52a 100644
--- a/database/gdb/gdb_core_config.go
+++ b/database/gdb/gdb_core_config.go
@@ -42,7 +42,8 @@ type ConfigNode struct {
 	LinkInfo             string        `json:"link"`                 // (Optional) Custom link information, when it is used, configuration Host/Port/User/Pass/Name are ignored.
 	MaxIdleConnCount     int           `json:"maxIdle"`              // (Optional) Max idle connection configuration for underlying connection pool.
 	MaxOpenConnCount     int           `json:"maxOpen"`              // (Optional) Max open connection configuration for underlying connection pool.
-	MaxConnLifetime      time.Duration `json:"maxLifetime"`          // (Optional) Max connection TTL configuration for underlying connection pool.
+	MaxConnIdleTime      time.Duration `json:"maxIdleTime"`          // (Optional) Max connection TTL configuration for underlying connection pool.
+	MaxConnLifeTime      time.Duration `json:"maxLifeTime"`          // (Optional) Max amount of time a connection may be idle before being closed.
 	QueryTimeout         time.Duration `json:"queryTimeout"`         // (Optional) Max query time for per dql.
 	ExecTimeout          time.Duration `json:"execTimeout"`          // (Optional) Max exec time for dml.
 	TranTimeout          time.Duration `json:"tranTimeout"`          // (Optional) Max exec time time for a transaction.
@@ -141,31 +142,60 @@ func (c *Core) GetLogger() *glog.Logger {
 	return c.logger
 }
 
-// SetMaxIdleConnCount sets the max idle connection count for underlying connection pool.
+// SetMaxIdleConnCount sets the maximum number of connections in the idle
+// connection pool.
+//
+// If MaxOpenConns is greater than 0 but less than the new MaxIdleConns,
+// then the new MaxIdleConns will be reduced to match the MaxOpenConns limit.
+//
+// If n <= 0, no idle connections are retained.
+//
+// The default max idle connections is currently 2. This may change in
+// a future release.
 func (c *Core) SetMaxIdleConnCount(n int) {
 	c.config.MaxIdleConnCount = n
 }
 
-// SetMaxOpenConnCount sets the max open connection count for underlying connection pool.
+// SetMaxOpenConnCount sets the maximum number of open connections to the database.
+//
+// If MaxIdleConns is greater than 0 and the new MaxOpenConns is less than
+// MaxIdleConns, then MaxIdleConns will be reduced to match the new
+// MaxOpenConns limit.
+//
+// If n <= 0, then there is no limit on the number of open connections.
+// The default is 0 (unlimited).
 func (c *Core) SetMaxOpenConnCount(n int) {
 	c.config.MaxOpenConnCount = n
 }
 
-// SetMaxConnLifetime sets the connection TTL for underlying connection pool.
-// If parameter `d` <= 0, it means the connection never expires.
-func (c *Core) SetMaxConnLifetime(d time.Duration) {
-	c.config.MaxConnLifetime = d
+// SetMaxConnIdleTime sets the maximum amount of time a connection may be idle.
+//
+// Expired connections may be closed lazily before reuse.
+//
+// If d <= 0, connections are not closed due to a connection's idle time.
+func (c *Core) SetMaxConnIdleTime(d time.Duration) {
+	c.config.MaxConnIdleTime = d
+}
+
+// SetMaxConnLifeTime sets the maximum amount of time a connection may be reused.
+//
+// Expired connections may be closed lazily before reuse.
+//
+// If d <= 0, connections are not closed due to a connection's age.
+func (c *Core) SetMaxConnLifeTime(d time.Duration) {
+	c.config.MaxConnLifeTime = d
 }
 
 // String returns the node as string.
 func (node *ConfigNode) String() string {
 	return fmt.Sprintf(
-		`%s@%s:%s,%s,%s,%s,%s,%v,%d-%d-%d#%s`,
+		`%s@%s:%s,%s,%s,%s,%s,%v,%d-%d-%d-%d#%s`,
 		node.User, node.Host, node.Port,
 		node.Name, node.Type, node.Role, node.Charset, node.Debug,
 		node.MaxIdleConnCount,
 		node.MaxOpenConnCount,
-		node.MaxConnLifetime,
+		node.MaxConnIdleTime,
+		node.MaxConnLifeTime,
 		node.LinkInfo,
 	)
 }
diff --git a/database/gdb/gdb_core_structure.go b/database/gdb/gdb_core_structure.go
index de5b9e770..8e28f239b 100644
--- a/database/gdb/gdb_core_structure.go
+++ b/database/gdb/gdb_core_structure.go
@@ -149,7 +149,7 @@ func (c *Core) convertFieldValueToLocalValue(fieldValue interface{}, fieldType s
 // mappingAndFilterData automatically mappings the map key to table field and removes
 // all key-value pairs that are not the field of given table.
 func (c *Core) mappingAndFilterData(schema, table string, data map[string]interface{}, filter bool) (map[string]interface{}, error) {
-	if fieldsMap, err := c.db.TableFields(table, schema); err == nil {
+	if fieldsMap, err := c.db.TableFields(nil, table, schema); err == nil {
 		fieldsKeyMap := make(map[string]interface{}, len(fieldsMap))
 		for k, _ := range fieldsMap {
 			fieldsKeyMap[k] = nil
diff --git a/database/gdb/gdb_driver_mssql.go b/database/gdb/gdb_driver_mssql.go
index 6ba855489..f288187c9 100644
--- a/database/gdb/gdb_driver_mssql.go
+++ b/database/gdb/gdb_driver_mssql.go
@@ -203,7 +203,9 @@ func (d *DriverMssql) Tables(schema ...string) (tables []string, err error) {
 }
 
 // TableFields retrieves and returns the fields information of specified table of current schema.
-func (d *DriverMssql) TableFields(table string, schema ...string) (fields map[string]*TableField, err error) {
+//
+// Also see DriverMysql.TableFields.
+func (d *DriverMssql) TableFields(link Link, table string, schema ...string) (fields map[string]*TableField, err error) {
 	charL, charR := d.GetChars()
 	table = gstr.Trim(table, charL+charR)
 	if gstr.Contains(table, " ") {
@@ -213,18 +215,21 @@ func (d *DriverMssql) TableFields(table string, schema ...string) (fields map[st
 	if len(schema) > 0 && schema[0] != "" {
 		checkSchema = schema[0]
 	}
-	v, _ := internalCache.GetOrSetFunc(
-		fmt.Sprintf(`mssql_table_fields_%s_%s@group:%s`, table, checkSchema, d.GetGroup()),
-		func() (interface{}, error) {
-			var (
-				result Result
-				link   *sql.DB
-			)
+	tableFieldsCacheKey := fmt.Sprintf(
+		`mssql_table_fields_%s_%s@group:%s`,
+		table, checkSchema, d.GetGroup(),
+	)
+	v := tableFieldsMap.GetOrSetFuncLock(tableFieldsCacheKey, func() interface{} {
+		var (
+			result Result
+		)
+		if link == nil {
 			link, err = d.db.GetSlave(checkSchema)
 			if err != nil {
-				return nil, err
+				return nil
 			}
-			structureSql := fmt.Sprintf(`
+		}
+		structureSql := fmt.Sprintf(`
 SELECT 
 	a.name Field,
 	CASE b.name 
@@ -252,29 +257,29 @@ LEFT JOIN sys.extended_properties g ON a.id=g.major_id AND a.colid=g.minor_id
 LEFT JOIN sys.extended_properties f ON d.id=f.major_id AND f.minor_id =0
 WHERE d.name='%s'
 ORDER BY a.id,a.colorder`,
-				strings.ToUpper(table),
-			)
-			structureSql, _ = gregex.ReplaceString(`[\n\r\s]+`, " ", gstr.Trim(structureSql))
-			result, err = d.db.DoGetAll(link, structureSql)
-			if err != nil {
-				return nil, err
+			strings.ToUpper(table),
+		)
+		structureSql, _ = gregex.ReplaceString(`[\n\r\s]+`, " ", gstr.Trim(structureSql))
+		result, err = d.db.DoGetAll(link, structureSql)
+		if err != nil {
+			return nil
+		}
+		fields = make(map[string]*TableField)
+		for i, m := range result {
+			fields[strings.ToLower(m["Field"].String())] = &TableField{
+				Index:   i,
+				Name:    strings.ToLower(m["Field"].String()),
+				Type:    strings.ToLower(m["Type"].String()),
+				Null:    m["Null"].Bool(),
+				Key:     m["Key"].String(),
+				Default: m["Default"].Val(),
+				Extra:   m["Extra"].String(),
+				Comment: m["Comment"].String(),
 			}
-			fields = make(map[string]*TableField)
-			for i, m := range result {
-				fields[strings.ToLower(m["Field"].String())] = &TableField{
-					Index:   i,
-					Name:    strings.ToLower(m["Field"].String()),
-					Type:    strings.ToLower(m["Type"].String()),
-					Null:    m["Null"].Bool(),
-					Key:     m["Key"].String(),
-					Default: m["Default"].Val(),
-					Extra:   m["Extra"].String(),
-					Comment: m["Comment"].String(),
-				}
-			}
-			return fields, nil
-		}, 0)
-	if err == nil {
+		}
+		return fields
+	})
+	if v != nil {
 		fields = v.(map[string]*TableField)
 	}
 	return
diff --git a/database/gdb/gdb_driver_mysql.go b/database/gdb/gdb_driver_mysql.go
index 5ac100350..9f6f6bf45 100644
--- a/database/gdb/gdb_driver_mysql.go
+++ b/database/gdb/gdb_driver_mysql.go
@@ -102,13 +102,16 @@ func (d *DriverMysql) Tables(schema ...string) (tables []string, err error) {
 // TableFields retrieves and returns the fields information of specified table of current
 // schema.
 //
+// The parameter `link` is optional, if given nil it automatically retrieves a raw sql connection
+// as its link to proceed necessary sql query.
+//
 // Note that it returns a map containing the field name and its corresponding fields.
 // As a map is unsorted, the TableField struct has a "Index" field marks its sequence in
 // the fields.
 //
 // It's using cache feature to enhance the performance, which is never expired util the
 // process restarts.
-func (d *DriverMysql) TableFields(table string, schema ...string) (fields map[string]*TableField, err error) {
+func (d *DriverMysql) TableFields(link Link, table string, schema ...string) (fields map[string]*TableField, err error) {
 	charL, charR := d.GetChars()
 	table = gstr.Trim(table, charL+charR)
 	if gstr.Contains(table, " ") {
@@ -118,40 +121,43 @@ func (d *DriverMysql) TableFields(table string, schema ...string) (fields map[st
 	if len(schema) > 0 && schema[0] != "" {
 		checkSchema = schema[0]
 	}
-	v, _ := internalCache.GetOrSetFunc(
-		fmt.Sprintf(`mysql_table_fields_%s_%s@group:%s`, table, checkSchema, d.GetGroup()),
-		func() (interface{}, error) {
-			var (
-				result Result
-				link   *sql.DB
-			)
+	tableFieldsCacheKey := fmt.Sprintf(
+		`mysql_table_fields_%s_%s@group:%s`,
+		table, checkSchema, d.GetGroup(),
+	)
+	v := tableFieldsMap.GetOrSetFuncLock(tableFieldsCacheKey, func() interface{} {
+		var (
+			result Result
+		)
+		if link == nil {
 			link, err = d.db.GetSlave(checkSchema)
 			if err != nil {
-				return nil, err
+				return nil
 			}
-			result, err = d.db.DoGetAll(
-				link,
-				fmt.Sprintf(`SHOW FULL COLUMNS FROM %s`, d.db.QuoteWord(table)),
-			)
-			if err != nil {
-				return nil, err
+		}
+		result, err = d.db.DoGetAll(
+			link,
+			fmt.Sprintf(`SHOW FULL COLUMNS FROM %s`, d.db.QuoteWord(table)),
+		)
+		if err != nil {
+			return nil
+		}
+		fields = make(map[string]*TableField)
+		for i, m := range result {
+			fields[m["Field"].String()] = &TableField{
+				Index:   i,
+				Name:    m["Field"].String(),
+				Type:    m["Type"].String(),
+				Null:    m["Null"].Bool(),
+				Key:     m["Key"].String(),
+				Default: m["Default"].Val(),
+				Extra:   m["Extra"].String(),
+				Comment: m["Comment"].String(),
 			}
-			fields = make(map[string]*TableField)
-			for i, m := range result {
-				fields[m["Field"].String()] = &TableField{
-					Index:   i,
-					Name:    m["Field"].String(),
-					Type:    m["Type"].String(),
-					Null:    m["Null"].Bool(),
-					Key:     m["Key"].String(),
-					Default: m["Default"].Val(),
-					Extra:   m["Extra"].String(),
-					Comment: m["Comment"].String(),
-				}
-			}
-			return fields, nil
-		}, 0)
-	if err == nil {
+		}
+		return fields
+	})
+	if v != nil {
 		fields = v.(map[string]*TableField)
 	}
 	return
diff --git a/database/gdb/gdb_driver_oracle.go b/database/gdb/gdb_driver_oracle.go
index e0bac602f..f8011b91a 100644
--- a/database/gdb/gdb_driver_oracle.go
+++ b/database/gdb/gdb_driver_oracle.go
@@ -179,7 +179,9 @@ func (d *DriverOracle) Tables(schema ...string) (tables []string, err error) {
 }
 
 // TableFields retrieves and returns the fields information of specified table of current schema.
-func (d *DriverOracle) TableFields(table string, schema ...string) (fields map[string]*TableField, err error) {
+//
+// Also see DriverMysql.TableFields.
+func (d *DriverOracle) TableFields(link Link, table string, schema ...string) (fields map[string]*TableField, err error) {
 	charL, charR := d.GetChars()
 	table = gstr.Trim(table, charL+charR)
 	if gstr.Contains(table, " ") {
@@ -189,11 +191,14 @@ func (d *DriverOracle) TableFields(table string, schema ...string) (fields map[s
 	if len(schema) > 0 && schema[0] != "" {
 		checkSchema = schema[0]
 	}
-	v, _ := internalCache.GetOrSetFunc(
-		fmt.Sprintf(`oracle_table_fields_%s_%s@group:%s`, table, checkSchema, d.GetGroup()),
-		func() (interface{}, error) {
-			result := (Result)(nil)
-			structureSql := fmt.Sprintf(`
+	tableFieldsCacheKey := fmt.Sprintf(
+		`oracle_table_fields_%s_%s@group:%s`,
+		table, checkSchema, d.GetGroup(),
+	)
+	v := tableFieldsMap.GetOrSetFuncLock(tableFieldsCacheKey, func() interface{} {
+		var (
+			result       Result
+			structureSql = fmt.Sprintf(`
 SELECT 
 	COLUMN_NAME AS FIELD, 
 	CASE DATA_TYPE  
@@ -203,22 +208,29 @@ SELECT
 FROM USER_TAB_COLUMNS WHERE TABLE_NAME = '%s' ORDER BY COLUMN_ID`,
 				strings.ToUpper(table),
 			)
-			structureSql, _ = gregex.ReplaceString(`[\n\r\s]+`, " ", gstr.Trim(structureSql))
-			result, err = d.db.GetAll(structureSql)
+		)
+		structureSql, _ = gregex.ReplaceString(`[\n\r\s]+`, " ", gstr.Trim(structureSql))
+		if link == nil {
+			link, err = d.db.GetSlave(checkSchema)
 			if err != nil {
-				return nil, err
+				return nil
 			}
-			fields = make(map[string]*TableField)
-			for i, m := range result {
-				fields[strings.ToLower(m["FIELD"].String())] = &TableField{
-					Index: i,
-					Name:  strings.ToLower(m["FIELD"].String()),
-					Type:  strings.ToLower(m["TYPE"].String()),
-				}
+		}
+		result, err = d.db.DoGetAll(link, structureSql)
+		if err != nil {
+			return nil
+		}
+		fields = make(map[string]*TableField)
+		for i, m := range result {
+			fields[strings.ToLower(m["FIELD"].String())] = &TableField{
+				Index: i,
+				Name:  strings.ToLower(m["FIELD"].String()),
+				Type:  strings.ToLower(m["TYPE"].String()),
 			}
-			return fields, nil
-		}, 0)
-	if err == nil {
+		}
+		return fields
+	})
+	if v != nil {
 		fields = v.(map[string]*TableField)
 	}
 	return
diff --git a/database/gdb/gdb_driver_pgsql.go b/database/gdb/gdb_driver_pgsql.go
index a047733a2..95cf65087 100644
--- a/database/gdb/gdb_driver_pgsql.go
+++ b/database/gdb/gdb_driver_pgsql.go
@@ -111,7 +111,9 @@ func (d *DriverPgsql) Tables(schema ...string) (tables []string, err error) {
 }
 
 // TableFields retrieves and returns the fields information of specified table of current schema.
-func (d *DriverPgsql) TableFields(table string, schema ...string) (fields map[string]*TableField, err error) {
+//
+// Also see DriverMysql.TableFields.
+func (d *DriverPgsql) TableFields(link Link, table string, schema ...string) (fields map[string]*TableField, err error) {
 	charL, charR := d.GetChars()
 	table = gstr.Trim(table, charL+charR)
 	if gstr.Contains(table, " ") {
@@ -122,41 +124,43 @@ func (d *DriverPgsql) TableFields(table string, schema ...string) (fields map[st
 	if len(schema) > 0 && schema[0] != "" {
 		checkSchema = schema[0]
 	}
-	v, _ := internalCache.GetOrSetFunc(
-		fmt.Sprintf(`pgsql_table_fields_%s_%s@group:%s`, table, checkSchema, d.GetGroup()),
-		func() (interface{}, error) {
-			var (
-				result Result
-				link   *sql.DB
-			)
-			link, err = d.db.GetSlave(checkSchema)
-			if err != nil {
-				return nil, err
-			}
-			structureSql := fmt.Sprintf(`
+	tableFieldsCacheKey := fmt.Sprintf(
+		`pgsql_table_fields_%s_%s@group:%s`,
+		table, checkSchema, d.GetGroup(),
+	)
+	v := tableFieldsMap.GetOrSetFuncLock(tableFieldsCacheKey, func() interface{} {
+		var (
+			result       Result
+			structureSql = fmt.Sprintf(`
 SELECT a.attname AS field, t.typname AS type FROM pg_class c, pg_attribute a 
 LEFT OUTER JOIN pg_description b ON a.attrelid=b.objoid AND a.attnum = b.objsubid,pg_type t
 WHERE c.relname = '%s' and a.attnum > 0 and a.attrelid = c.oid and a.atttypid = t.oid 
 ORDER BY a.attnum`,
 				strings.ToLower(table),
 			)
-			structureSql, _ = gregex.ReplaceString(`[\n\r\s]+`, " ", gstr.Trim(structureSql))
-			result, err = d.db.DoGetAll(link, structureSql)
+		)
+		structureSql, _ = gregex.ReplaceString(`[\n\r\s]+`, " ", gstr.Trim(structureSql))
+		if link == nil {
+			link, err = d.db.GetSlave(checkSchema)
 			if err != nil {
-				return nil, err
+				return nil
 			}
-
-			fields = make(map[string]*TableField)
-			for i, m := range result {
-				fields[m["field"].String()] = &TableField{
-					Index: i,
-					Name:  m["field"].String(),
-					Type:  m["type"].String(),
-				}
+		}
+		result, err = d.db.DoGetAll(link, structureSql)
+		if err != nil {
+			return nil
+		}
+		fields = make(map[string]*TableField)
+		for i, m := range result {
+			fields[m["field"].String()] = &TableField{
+				Index: i,
+				Name:  m["field"].String(),
+				Type:  m["type"].String(),
 			}
-			return fields, nil
-		}, 0)
-	if err == nil {
+		}
+		return fields
+	})
+	if v != nil {
 		fields = v.(map[string]*TableField)
 	}
 	return
diff --git a/database/gdb/gdb_driver_sqlite.go b/database/gdb/gdb_driver_sqlite.go
index ed577217a..ba000fbbb 100644
--- a/database/gdb/gdb_driver_sqlite.go
+++ b/database/gdb/gdb_driver_sqlite.go
@@ -93,7 +93,9 @@ func (d *DriverSqlite) Tables(schema ...string) (tables []string, err error) {
 }
 
 // TableFields retrieves and returns the fields information of specified table of current schema.
-func (d *DriverSqlite) TableFields(table string, schema ...string) (fields map[string]*TableField, err error) {
+//
+// Also see DriverMysql.TableFields.
+func (d *DriverSqlite) TableFields(link Link, table string, schema ...string) (fields map[string]*TableField, err error) {
 	charL, charR := d.GetChars()
 	table = gstr.Trim(table, charL+charR)
 	if gstr.Contains(table, " ") {
@@ -103,32 +105,35 @@ func (d *DriverSqlite) TableFields(table string, schema ...string) (fields map[s
 	if len(schema) > 0 && schema[0] != "" {
 		checkSchema = schema[0]
 	}
-	v, _ := internalCache.GetOrSetFunc(
-		fmt.Sprintf(`sqlite_table_fields_%s_%s@group:%s`, table, checkSchema, d.GetGroup()),
-		func() (interface{}, error) {
-			var (
-				result Result
-				link   *sql.DB
-			)
+	tableFieldsCacheKey := fmt.Sprintf(
+		`sqlite_table_fields_%s_%s@group:%s`,
+		table, checkSchema, d.GetGroup(),
+	)
+	v := tableFieldsMap.GetOrSetFuncLock(tableFieldsCacheKey, func() interface{} {
+		var (
+			result Result
+		)
+		if link == nil {
 			link, err = d.db.GetSlave(checkSchema)
 			if err != nil {
-				return nil, err
+				return nil
 			}
-			result, err = d.db.DoGetAll(link, fmt.Sprintf(`PRAGMA TABLE_INFO(%s)`, table))
-			if err != nil {
-				return nil, err
+		}
+		result, err = d.db.DoGetAll(link, fmt.Sprintf(`PRAGMA TABLE_INFO(%s)`, table))
+		if err != nil {
+			return nil
+		}
+		fields = make(map[string]*TableField)
+		for i, m := range result {
+			fields[strings.ToLower(m["name"].String())] = &TableField{
+				Index: i,
+				Name:  strings.ToLower(m["name"].String()),
+				Type:  strings.ToLower(m["type"].String()),
 			}
-			fields = make(map[string]*TableField)
-			for i, m := range result {
-				fields[strings.ToLower(m["name"].String())] = &TableField{
-					Index: i,
-					Name:  strings.ToLower(m["name"].String()),
-					Type:  strings.ToLower(m["type"].String()),
-				}
-			}
-			return fields, nil
-		}, 0)
-	if err == nil {
+		}
+		return fields
+	})
+	if v != nil {
 		fields = v.(map[string]*TableField)
 	}
 	return
diff --git a/database/gdb/gdb_model_fields.go b/database/gdb/gdb_model_fields.go
index bbcb5978f..c10e00461 100644
--- a/database/gdb/gdb_model_fields.go
+++ b/database/gdb/gdb_model_fields.go
@@ -94,7 +94,7 @@ func (m *Model) GetFieldsStr(prefix ...string) string {
 	if len(prefix) > 0 {
 		prefixStr = prefix[0]
 	}
-	tableFields, err := m.db.TableFields(m.tables)
+	tableFields, err := m.TableFields(m.tables)
 	if err != nil {
 		panic(err)
 	}
@@ -131,7 +131,7 @@ func (m *Model) GetFieldsExStr(fields string, prefix ...string) string {
 	if len(prefix) > 0 {
 		prefixStr = prefix[0]
 	}
-	tableFields, err := m.db.TableFields(m.tables)
+	tableFields, err := m.TableFields(m.tables)
 	if err != nil {
 		panic(err)
 	}
@@ -159,7 +159,7 @@ func (m *Model) GetFieldsExStr(fields string, prefix ...string) string {
 
 // HasField determine whether the field exists in the table.
 func (m *Model) HasField(field string) (bool, error) {
-	tableFields, err := m.db.TableFields(m.tables)
+	tableFields, err := m.TableFields(m.tables)
 	if err != nil {
 		return false, err
 	}
diff --git a/database/gdb/gdb_model_select.go b/database/gdb/gdb_model_select.go
index 1cd5139fa..962592b33 100644
--- a/database/gdb/gdb_model_select.go
+++ b/database/gdb/gdb_model_select.go
@@ -84,7 +84,7 @@ func (m *Model) getFieldsFiltered() string {
 			panic("function FieldsEx supports only single table operations")
 		}
 		// Filter table fields with fieldEx.
-		tableFields, err := m.db.TableFields(m.tables)
+		tableFields, err := m.TableFields(m.tables)
 		if err != nil {
 			panic(err)
 		}
diff --git a/database/gdb/gdb_model_time.go b/database/gdb/gdb_model_time.go
index ce14d831e..e167fbb35 100644
--- a/database/gdb/gdb_model_time.go
+++ b/database/gdb/gdb_model_time.go
@@ -93,7 +93,7 @@ func (m *Model) getSoftFieldNameDeleted(table ...string) (field string) {
 
 // getSoftFieldName retrieves and returns the field name of the table for possible key.
 func (m *Model) getSoftFieldName(table string, keys []string) (field string) {
-	fieldsMap, _ := m.db.TableFields(table)
+	fieldsMap, _ := m.TableFields(table)
 	if len(fieldsMap) > 0 {
 		for _, key := range keys {
 			field, _ = gutil.MapPossibleItemByKey(
diff --git a/database/gdb/gdb_model_utility.go b/database/gdb/gdb_model_utility.go
index 93ede1a04..93890326b 100644
--- a/database/gdb/gdb_model_utility.go
+++ b/database/gdb/gdb_model_utility.go
@@ -28,12 +28,31 @@ func (m *Model) getModel() *Model {
 	}
 }
 
+// TableFields retrieves and returns the fields information of specified table of current
+// schema.
+//
+// Also see DriverMysql.TableFields.
+func (m *Model) TableFields(table string, schema ...string) (fields map[string]*TableField, err error) {
+	var (
+		link Link
+	)
+	if m.tx != nil {
+		link = m.tx.tx
+	} else {
+		link, err = m.db.GetSlave(schema...)
+		if err != nil {
+			return
+		}
+	}
+	return m.db.TableFields(link, table, schema...)
+}
+
 // mappingAndFilterToTableFields mappings and changes given field name to really table field name.
 // Eg:
 // ID        -> id
 // NICK_Name -> nickname
 func (m *Model) mappingAndFilterToTableFields(fields []string, filter bool) []string {
-	fieldsMap, err := m.db.TableFields(m.tables)
+	fieldsMap, err := m.TableFields(m.tables)
 	if err != nil || len(fieldsMap) == 0 {
 		return fields
 	}
@@ -188,7 +207,7 @@ func (m *Model) getLink(master bool) Link {
 // "user", "user u", "user as u, user_detail as ud".
 func (m *Model) getPrimaryKey() string {
 	table := gstr.SplitAndTrim(m.tables, " ")[0]
-	tableFields, err := m.db.TableFields(table)
+	tableFields, err := m.TableFields(table)
 	if err != nil {
 		return ""
 	}
diff --git a/database/gdb/gdb_z_init_test.go b/database/gdb/gdb_z_init_test.go
index fe9fcc47a..abe205257 100644
--- a/database/gdb/gdb_z_init_test.go
+++ b/database/gdb/gdb_z_init_test.go
@@ -52,7 +52,7 @@ func init() {
 		Weight:           1,
 		MaxIdleConnCount: 10,
 		MaxOpenConnCount: 10,
-		MaxConnLifetime:  600,
+		MaxConnLifeTime:  600,
 	}
 	nodePrefix := configNode
 	nodePrefix.Prefix = TableNamePrefix1
diff --git a/database/gdb/gdb_z_mysql_internal_test.go b/database/gdb/gdb_z_mysql_internal_test.go
index 736a1c1f0..ed80711a6 100644
--- a/database/gdb/gdb_z_mysql_internal_test.go
+++ b/database/gdb/gdb_z_mysql_internal_test.go
@@ -45,7 +45,7 @@ func init() {
 		Weight:           1,
 		MaxIdleConnCount: 10,
 		MaxOpenConnCount: 10,
-		MaxConnLifetime:  600,
+		MaxConnLifeTime:  600,
 	}
 	AddConfigNode(DefaultGroupName, configNode)
 	// Default db.
diff --git a/version.go b/version.go
index 04fce82b3..189fb2e19 100644
--- a/version.go
+++ b/version.go
@@ -1,4 +1,4 @@
 package gf
 
-const VERSION = "v1.15.5"
+const VERSION = "v1.15.6"
 const AUTHORS = "john<john@goframe.org>"