A deprecated alias for a variable. More...

#include <sys_vars.h>

Inheritance diagram for Sys_var_deprecated_alias:

Public Member Functions
	Sys_var_deprecated_alias (const char *name_arg, sys_var &base_var)

Public Member Functions inherited from Sys_var_alias
	Sys_var_alias (const char *name_arg, sys_var &base_var)

sys_var &	get_base_var ()

void	cleanup () override
	All the cleanup procedures should be performed here. More...

sys_var_pluginvar *	cast_pluginvar () override
	downcast for sys_var_pluginvar. More...

void	update_default (longlong new_def_value) override

longlong	get_default () override

longlong	get_min_value () override

ulonglong	get_max_value () override

ulong	get_var_type () override
	Returns variable type. More...

void	set_arg_source (get_opt_arg_source *arg_source) override

void	set_is_plugin (bool is_plugin) override

bool	is_non_persistent () override

void	saved_value_to_string (THD thd, set_var var, char *def_val) override
	This function converts value stored in save_result to string. More...

bool	check_update_type (Item_result type) override

enum_variable_source	get_source () override

const char *	get_source_name () override

void	set_source (enum_variable_source src) override

bool	set_source_name (const char *path) override

bool	set_user (const char *usr) override

const char *	get_user () override

const char *	get_host () override

bool	set_host (const char *hst) override

ulonglong	get_timestamp () const override

void	set_user_host (THD *thd) override

void	set_timestamp () override

void	set_timestamp (ulonglong ts) override

Public Member Functions inherited from sys_var
	sys_var (sys_var_chain chain, const char name_arg, const char comment, int flag_args, ptrdiff_t off, int getopt_id, enum get_opt_arg_type getopt_arg_type, SHOW_TYPE show_val_type_arg, longlong def_val, PolyLock lock, enum binlog_status_enum binlog_status_arg, on_check_function on_check_func, on_update_function on_update_func, const char substitute, int parse_flag, sys_var persisted_alias=nullptr, bool is_persisted_deprecated=false)
	sys_var constructor More...

virtual	~sys_var ()=default

const char *	get_deprecation_substitute ()

bool	check (THD thd, set_var var)

const uchar *	value_ptr (THD running_thd, THD target_thd, enum_var_type type, std::string_view keycache_name)

const uchar *	value_ptr (THD *thd, enum_var_type type, std::string_view keycache_name)

my_option *	get_option ()

bool	set_default (THD thd, set_var var)
	Update the system variable with the default value from either session or global scope. More...

bool	update (THD thd, set_var var)

SHOW_TYPE	show_type ()

int	scope () const

const CHARSET_INFO *	charset (THD *thd)

bool	is_readonly () const

bool	not_visible () const

bool	is_trilevel () const

bool	is_persist_readonly () const

bool	is_parse_early () const

bool	is_sensitive () const

bool	is_hint_updateable () const
	Check if the variable can be set using SET_VAR hint. More...

bool	is_struct ()
	the following is only true for keycache variables, that support the syntax @keycache_name.variable_name More...

bool	is_written_to_binlog (enum_var_type type)

bool	check_scope (enum_var_type query_type)
	Return true for success if: Global query and variable scope is GLOBAL or SESSION, or Session query and variable scope is SESSION or ONLY_SESSION. More...

bool	is_global_persist (enum_var_type type)

bool	is_settable_at_command_line ()
	Return true if settable at the command line. More...

bool	register_option (std::vector< my_option > *array, int parse_flags)

void	do_deprecated_warning (THD *thd)

Item *	copy_value (THD *thd)
	Create item from system variable value. More...

void	save_default (THD thd, set_var var)

bool	check_if_sensitive_in_context (THD *, bool suppress_errors=true) const

Private Attributes
std::string	m_comment

Additional Inherited Members
Public Types inherited from sys_var
enum	flag_enum { GLOBAL = 0x0001 , SESSION = 0x0002 , ONLY_SESSION = 0x0004 , SCOPE_MASK = 0x03FF , READONLY = 0x0400 , ALLOCATED = 0x0800 , INVISIBLE = 0x1000 , TRI_LEVEL = 0x2000 , NOTPERSIST = 0x4000 , HINT_UPDATEABLE = 0x8000 , PERSIST_AS_READ_ONLY = 0x10000 , SENSITIVE = 0x20000 }

enum	binlog_status_enum { VARIABLE_NOT_IN_BINLOG , SESSION_VARIABLE_IN_BINLOG }
	Enumeration type to indicate for a system variable whether it will be written to the binlog or not. More...

Public Attributes inherited from sys_var
sys_var *	next

LEX_CSTRING	name

sys_var *	m_persisted_alias
	If the variable has an alias in the persisted variables file, this should point to it. More...

bool	m_is_persisted_deprecated
	If m_persist_alias is set, and the current variable is deprecated and m_persist_alias is the recommended substitute, then this flag should be set to true. More...

enum sys_var::binlog_status_enum	binlog_status

Static Public Attributes inherited from sys_var
static const int	PARSE_EARLY = 1

static const int	PARSE_NORMAL = 2

Protected Types inherited from sys_var
typedef bool(*	on_check_function) (sys_var self, THD thd, set_var *var)

typedef bool(*	pre_update_function) (sys_var self, THD thd, set_var *var)

typedef bool(*	on_update_function) (sys_var self, THD thd, enum_var_type type)

Protected Member Functions inherited from Sys_var_alias
	Sys_var_alias (const char name_arg, sys_var &base_var, const char deprecation_substitute_arg, sys_var *persisted_alias, bool is_persisted_deprecated)
	Special constructor used to implement Sys_var_deprecated alias. More...

const uchar *	session_value_ptr (THD running_thd, THD target_thd, std::string_view keycache_name) override
	A pointer to a value of the variable for SHOW. More...

const uchar *	global_value_ptr (THD *thd, std::string_view keycache_name) override

Protected Member Functions inherited from sys_var
uchar *	session_var_ptr (THD *thd)
	A pointer to a storage area of the variable, to the raw data. More...

uchar *	global_var_ptr ()

Protected Attributes inherited from sys_var
int	flags
	or'ed flag_enum values More...

int	m_parse_flag
	either PARSE_EARLY or PARSE_NORMAL. More...

const SHOW_TYPE	show_val_type
	what value_ptr() returns for sql_show.cc More...

my_option	option
	min, max, default values are stored here More...

PolyLock *	guard
	second lock that protects the variable More...

ptrdiff_t	offset
	offset to the value from global_system_variables More...

on_check_function	on_check

pre_update_function	pre_update
	Pointer to function to be invoked before updating system variable (but after calling on_check hook), while we do not hold any locks yet. More...

on_update_function	on_update

const char *const	deprecation_substitute

bool	is_os_charset
	true if the value is in character_set_filesystem More...

struct get_opt_arg_source	source

char	user [USERNAME_CHAR_LENGTH+1]

char	host [HOSTNAME_LENGTH+1]

ulonglong	timestamp

Detailed Description

A deprecated alias for a variable.

This tool allows us to rename system variables without breaking backward compatibility.

Procedure for a developer to create a new name for a variable in version X and remove the old name in version X+1:

In version X:
- Change the string passed to the Sys_var constructor for the variable the new new name. All existing code for this should remain as it is.
- Create a Sys_var_deprecated_alias taking the old name as the first argument and the Sys_var object having the new name as the second argument.
In version X+1:
- Remove the Sys_var_deprecated_alias.

This has the following effects in version X:

Both variables coexist. They are both visible in performance_schema tables and accessible in SET statements and SELECT @variable statements. Both variables always have the same values.
A SET statement using either the old name or the new name changes the value of both variables.
A SET statement using the old name generates a deprecation warning.
The procedure that loads persisted variables from file accepts either the old name, or the new name, or both. It generates a deprecation warning in case only the old name exists in the file. A SET PERSIST statement writes both variables to the file.

The procedures for a user to upgrade or downgrade are:

After upgrade from version X-1 to X, all persisted variables retain their persisted values. User will see deprecation warnings when loading the persisted variables file, with instructions to run a SET PERSIST statement any time before the next upgrade to X+1.
While on version X, user needs to run a SET PERSIST statement any time before upgrading to X+1. Due to the logic described above, it will write both variables to the file.
While on version X, user needs to change their cnf files, command-line arguments, and @variables accessed through application logic, to use the new names, before upgrading to X+1. The deprecation warnings will help identify the relevant places to update.
After upgrade from X to X+1, the server will read the old variables from the file. Since this version does not know about the old variables, it will ignore them and print a warning. The user can remove the unknown variable from the persisted variable file, and get rid of the warning, using RESET PERSIST OLD_VARIABLE_NAME.
After downgrade from version X+1 to version X, all persisted variables retain their values. User will not see deprecation warnings. If user needs to further downgrade to version X-1, user needs to first run SET PERSIST for some variable in order to rewrite the file so that the old variable names exist in the file.
After downgrade from version X to version X-1, all persisted variables retain their values. If the new variable names exist in the persisted variables file, a warning will be printed stating that the variable is not known and will be ignored. User can get rid of the warning by running RESET PERSIST NEW_VARIABLE_NAME.

Constructor & Destructor Documentation

◆ Sys_var_deprecated_alias()

Sys_var_deprecated_alias::Sys_var_deprecated_alias	(	const char *	name_arg,
		sys_var &	base_var
	)

inline

Member Data Documentation

◆ m_comment

std::string Sys_var_deprecated_alias::m_comment

private

The documentation for this class was generated from the following file:

sql/sys_vars.h

Public Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ Sys_var_deprecated_alias()

Member Data Documentation

◆ m_comment