System_variable_tracker Class Reference

Wrapper interface for all kinds of system variables. More...

#include <set_var.h>

Classes
struct	Cache
struct	Component
struct	Keycache
struct	Plugin
struct	Static

Public Types
enum	Lifetime { STATIC , KEYCACHE , PLUGIN , COMPONENT }
typedef Prealloced_array< System_variable_tracker, SYSTEM_VARIABLE_PREALLOC >	Array

Public Member Functions
	System_variable_tracker (const System_variable_tracker &)
	~System_variable_tracker ()
void	operator= (System_variable_tracker &&)
Lifetime	lifetime () const
bool	operator== (const System_variable_tracker &x) const
bool	is_keycache_var () const
bool	eq_static_sys_var (const sys_var *var) const
const char *	get_var_name () const
std::string_view	get_keycache_name () const
bool	is_hint_updateable () const
bool	access_system_variable (THD *thd, std::function< void(const System_variable_tracker &, sys_var *)> function={}, Suppress_not_found_error suppress_not_found_error=Suppress_not_found_error::NO, Force_sensitive_system_variable_access force_sensitive_variable_access=Force_sensitive_system_variable_access::NO, Is_already_locked is_already_locked=Is_already_locked::NO, Is_single_thread is_single_thread=Is_single_thread::NO) const
template<typename T >
std::optional< T >	access_system_variable (THD *thd, std::function< T(const System_variable_tracker &, sys_var *)> function, Suppress_not_found_error suppress_not_found_error=Suppress_not_found_error::NO, Force_sensitive_system_variable_access force_sensitive_variable_access=Force_sensitive_system_variable_access::NO, Is_already_locked is_already_locked=Is_already_locked::NO, Is_single_thread is_single_thread=Is_single_thread::NO) const
	Safely pass a sys_var object to a function. More...
SHOW_TYPE	cached_show_type () const
bool	cached_is_sensitive () const
bool	cached_is_applied_as_command_line () const

Static Public Member Functions
static System_variable_tracker	make_tracker (std::string_view prefix, std::string_view suffix)
	Static "constructor". More...
static System_variable_tracker	make_tracker (std::string_view multipart_name)
	Static "constructor". More...
static bool	enumerate_sys_vars (bool sort, enum enum_var_type type, bool strict, Array *output)
	Constructs an array of system variables for display to the user. More...

Public Attributes
friend	Array
sys_var *	m_static_var
struct {
sys_var *   m_static_var
}	m_static
char	m_keycache_var_name [NAME_LEN+sizeof(".key_cache_division_limit")]
	A dot-separated key cache name or, for a reduced form of key cache variable names, a key cache property name as specified by the caller of System_variable_tracker::make_traker(). More...
size_t	m_keycache_name_size
sys_var *	m_keycache_var
struct {
char   m_keycache_var_name [NAME_LEN+sizeof(".key_cache_division_limit")]
	A dot-separated key cache name or, for a reduced form of key cache variable names, a key cache property name as specified by the caller of System_variable_tracker::make_traker(). More...
size_t   m_keycache_name_size
sys_var *   m_keycache_var
}	m_keycache
char	m_plugin_var_name [NAME_LEN+1]
	A "_"-separated plugin-registered variables name. More...
sys_var *	m_plugin_var_cache
struct {
char   m_plugin_var_name [NAME_LEN+1]
	A "_"-separated plugin-registered variables name. More...
sys_var *   m_plugin_var_cache
}	m_plugin
char	m_component_var_name [NAME_LEN+sizeof('.')+NAME_LEN+1]
	A dot-separated component-registered variable name. More...
sys_var *	m_component_var_cache
struct {
char   m_component_var_name [NAME_LEN+sizeof('.')+NAME_LEN+1]
	A dot-separated component-registered variable name. More...
sys_var *   m_component_var_cache
}	m_component

Static Public Attributes
static constexpr size_t	SYSTEM_VARIABLE_PREALLOC = 200
	Number of system variable elements to preallocate. More...

Private Member Functions
	System_variable_tracker (Static, sys_var *var)
	System_variable_tracker (Keycache, std::string_view cache_name, sys_var *var)
	System_variable_tracker (Plugin, std::string_view name)
	System_variable_tracker (Component, std::string_view dot_separated_name)
	System_variable_tracker (Component, std::string_view component_name, std::string_view variable_name)
sys_var *	get_stable_var () const
bool	visit_plugin_variable (THD *, std::function< bool(sys_var *)>, Suppress_not_found_error, Is_already_locked, Is_single_thread) const
bool	visit_component_variable (THD *, std::function< bool(sys_var *)>, Suppress_not_found_error, Is_already_locked, Is_single_thread) const
void	cache_metadata (THD *thd, sys_var *v) const

Static Private Member Functions
static bool	enumerate_sys_vars_in_hash (collation_unordered_map< std::string, sys_var * > *hash, enum enum_var_type query_scope, bool strict, System_variable_tracker::Array *output)
static bool	names_are_same (const char *, const char *)

Private Attributes
Lifetime	m_tag
std::optional< Cache >	m_cache
union {
struct {
sys_var *   m_static_var
}   m_static
struct {
char   m_keycache_var_name [NAME_LEN+sizeof(".key_cache_division_limit")]
	A dot-separated key cache name or, for a reduced form of key cache variable names, a key cache property name as specified by the caller of System_variable_tracker::make_traker(). More...
size_t   m_keycache_name_size
sys_var *   m_keycache_var
}   m_keycache
struct {
char   m_plugin_var_name [NAME_LEN+1]
	A "_"-separated plugin-registered variables name. More...
sys_var *   m_plugin_var_cache
}   m_plugin
struct {
char   m_component_var_name [NAME_LEN+sizeof('.')+NAME_LEN+1]
	A dot-separated component-registered variable name. More...
sys_var *   m_component_var_cache
}   m_component
};

Static Private Attributes
static thread_local int	m_hash_lock_recursion_depth {0}
	A non-zero value suppresses LOCK_system_variables_hash guards in System_variable_tracker::access_system_variable. More...

Detailed Description

Wrapper interface for all kinds of system variables.

The interface encapsulates parse- and execution-time resolvers for all kinds of sys_var: regular (static) system variables MyISAM Multiple Key Cache variables plugin-registered variables component-registered variables Encapsulation of system variable resolving and data accessing tasks.

Member Typedef Documentation

Array

typedef Prealloced_array<System_variable_tracker, SYSTEM_VARIABLE_PREALLOC> System_variable_tracker::Array

Member Enumeration Documentation

Lifetime

enum System_variable_tracker::Lifetime

Enumerator
STATIC	for regular static variables
KEYCACHE	for MyISAM Multiple Key Cache variables
PLUGIN	for plugin-registered system variables
COMPONENT	for component-registered variables

Constructor & Destructor Documentation

System_variable_tracker() [1/6]

System_variable_tracker::System_variable_tracker ( Static  , sys_var *  var  )

private

System_variable_tracker() [2/6]

System_variable_tracker::System_variable_tracker ( Keycache  , std::string_view  cache_name, sys_var *  var  )

private

System_variable_tracker() [3/6]

System_variable_tracker::System_variable_tracker ( Plugin  , std::string_view  name  )

private

System_variable_tracker() [4/6]

System_variable_tracker::System_variable_tracker ( Component  , std::string_view  dot_separated_name  )

private

System_variable_tracker() [5/6]

System_variable_tracker::System_variable_tracker ( Component  , std::string_view  component_name, std::string_view  variable_name  )

private

System_variable_tracker() [6/6]

System_variable_tracker::System_variable_tracker

(

const System_variable_tracker &

x

)

~System_variable_tracker()

System_variable_tracker::~System_variable_tracker

(

)

Member Function Documentation

access_system_variable() [1/2]

template<typename T >

std::optional< T > System_variable_tracker::access_system_variable ( THD *  thd, std::function< T(const System_variable_tracker &, sys_var *)>  function, Suppress_not_found_error  suppress_not_found_error = Suppress_not_found_error::NO, Force_sensitive_system_variable_access  force_sensitive_variable_access = Force_sensitive_system_variable_access::NO, Is_already_locked  is_already_locked = Is_already_locked::NO, Is_single_thread  is_single_thread = Is_single_thread::NO  ) const

inline

Safely pass a sys_var object to a function.

Template variant.

access_system_variable() is the most important interface: it does necessary locks, if a dynamic variable is inaccessible then access_system_variable() exits returning empty std::option, otherwise it calls function and returns the result value of function to the caller.

See the pseudo code part at the comment above a signature of the non-template variant of access_system_variable() for details (replace "return true" with "return std::option{}" and "return false" with "return result value of anonymous function call").

Template Parameters

T	A type of a return value of the callback function.

Parameters

thd	A connection handler or nullptr.
function	A function to pass a sys_var object if the latest is accessible.
suppress_not_found_error	Suppress or output ER_UNKNOWN_SYSTEM_VARIABLE if a dynamic variable is unavailable.
force_sensitive_variable_access	Suppress privilege check for SENSITIVE variables.
is_already_locked	YES means LOCK_system_variables_hash has already been taken.
is_single_thread	YES means we are called from mysqld_main, during bootstrap.

Returns

No value if the dynamic variable is unavailable, otherwise a value of type T returned by the callback function.

access_system_variable() [2/2]

bool System_variable_tracker::access_system_variable	(	THD *	thd,
		std::function< void(const System_variable_tracker &, sys_var *)>	function = {},
		Suppress_not_found_error	suppress_not_found_error = Suppress_not_found_error::NO,
		Force_sensitive_system_variable_access	force_sensitive_variable_access = Force_sensitive_system_variable_access::NO,
		Is_already_locked	is_already_locked = Is_already_locked::NO,
		Is_single_thread	is_single_thread = Is_single_thread::NO
	)		const

Safely pass a sys_var object to a function. Non-template variant.

access_system_variable() is the most important interface:
it does necessary locks,
if a dynamic variable is inaccessible it exits,
otherwise it calls @p function.
access_system_variable() is reentrant:
being called recursively it suppresses double locks.

Simplified pseudo code of access_system_variable() implementation:

    if system variable is @@session_track_system_variables {

a special case: the system variable is static, but it references a comma-separated list of other system variables if function is not no-op { process @session_track_system_variables as plugin-registered one } else { return false // success } } if system variable is static or key cache variable { no dictionary/plugin locks needed call function(cached sys_var pointer) return false // success } if system variable is plugin-registered one { if need to hold LOCK_system_variables_hash { acquire read-only LOCK_system_variables_hash } if need to hold LOCK_plugin { acquire LOCK_plugin, unlock on exit } find sys_var if found { intern_plugin_lock } if this function acquired LOCK_plugin { release LOCK_plugin } if this function acquired LOCK_system_variables_hash { release LOCK_system_variables_hash } if not found or plugin is not in the PLUGIN_IS_READY state { return true // error: variable not found or } call function(found sys_var pointer) return false // success } if system variable is component-registered one { if need to hold LOCK_system_variables_hash(**) { acquire read-only LOCK_system_variables_hash, unlock on exit } find sys_var if not found { return true } call function(found sys_var pointer) return false // success }

Parameters

thd	A connection handler or nullptr.
function	An optional anonymous function to pass a sys_var object if the latest is accessible.
suppress_not_found_error	Suppress or output ER_UNKNOWN_SYSTEM_VARIABLE if a dynamic variable is unavailable.
force_sensitive_variable_access	Suppress privilege check for SENSITIVE variables.
is_already_locked	YES means LOCK_system_variables_hash has already been taken.
is_single_thread	YES means we are called from mysqld_main, during bootstrap.

Returns

True if the dynamic variable is unavailable, otherwise false.

cache_metadata()

void System_variable_tracker::cache_metadata ( THD *  thd, sys_var *  v  ) const

private

cached_is_applied_as_command_line()

bool System_variable_tracker::cached_is_applied_as_command_line ( ) const

inline

cached_is_sensitive()

bool System_variable_tracker::cached_is_sensitive ( ) const

inline

cached_show_type()

SHOW_TYPE System_variable_tracker::cached_show_type ( ) const

inline

enumerate_sys_vars()

bool System_variable_tracker::enumerate_sys_vars ( bool  sort, enum enum_var_type  query_scope, bool  strict, System_variable_tracker::Array *  output  )

static

Constructs an array of system variables for display to the user.

Parameters

output	Prealloced_array of elements for display
sort	If true, the system variables should be sorted
query_scope	OPT_GLOBAL or OPT_SESSION for SHOW GLOBAL|SESSION VARIABLES
strict	Use strict scope checking

Returns

True on error, false otherwise

Note

Requires r/o lock on LOCK_system_variables_hash.

enumerate_sys_vars_in_hash()

bool System_variable_tracker::enumerate_sys_vars_in_hash ( collation_unordered_map< std::string, sys_var * > *  hash, enum enum_var_type  query_scope, bool  strict, System_variable_tracker::Array *  output  )

staticprivate

eq_static_sys_var()

bool System_variable_tracker::eq_static_sys_var ( const sys_var *  var ) const

inline

get_keycache_name()

std::string_view System_variable_tracker::get_keycache_name ( ) const

inline

Returns

1) not normalized names of MyISAM Multiple Key Caches, also can return empty string for the implicit prefix (i.e. implicit "DEFAULT."). 2) empty string for the rest of system variables.

get_stable_var()

sys_var * System_variable_tracker::get_stable_var ( ) const

inlineprivate

get_var_name()

const char * System_variable_tracker::get_var_name

(

)

const

Returns

1) normalized names of regular system variables; 2) user-specified dot-separated names of key cache variables, or user-specified unqualified names of default key cache property names; 3) user-specified names of plugin-registered variables; 4) user-specified dot-separated names of component-registered variables.

is_hint_updateable()

bool System_variable_tracker::is_hint_updateable ( ) const

inline

Returns

true if the underlying variable can be referenced in the SET_VAR optimizer hint syntax, otherwise false.

is_keycache_var()

bool System_variable_tracker::is_keycache_var ( ) const

inline

lifetime()

Lifetime System_variable_tracker::lifetime ( ) const

inline

make_tracker() [1/2]

System_variable_tracker System_variable_tracker::make_tracker ( std::string_view  multipart_name )

static

Static "constructor".

Note

This function requires no locks and allocates nothing on memory heaps.

Parameters

multipart_name

Variable name, optionally dot-separated.

Returns

System_variable_tracker object

make_tracker() [2/2]

System_variable_tracker System_variable_tracker::make_tracker ( std::string_view  prefix, std::string_view  suffix  )

static

Static "constructor".

Note

This function requires no locks and allocates nothing on memory heaps.

Parameters

prefix	One of: component name, MyISAM Multiple Key Cache name, or empty string.
suffix	In a dot-separated syntax (prefix is mandatory): component-registered variable name, or MyISAM Multiple Key Cache property name. Otherwise (is empty): name of static or plugin-registered variables.

Returns

System_variable_tracker object

names_are_same()

bool System_variable_tracker::names_are_same ( const char *  a, const char *  b  )

staticprivate

operator=()

void System_variable_tracker::operator=

(

System_variable_tracker &&

x

)

operator==()

bool System_variable_tracker::operator== ( const System_variable_tracker &  x ) const

inline

visit_component_variable()

bool System_variable_tracker::visit_component_variable ( THD *  thd, std::function< bool(sys_var *)>  function, Suppress_not_found_error  suppress_not_found_error, Is_already_locked  is_already_locked, Is_single_thread  is_single_thread  ) const

private

visit_plugin_variable()

bool System_variable_tracker::visit_plugin_variable ( THD *  thd, std::function< bool(sys_var *)>  function, Suppress_not_found_error  suppress_not_found_error, Is_already_locked  is_already_locked, Is_single_thread  is_single_thread  ) const

private

Member Data Documentation

union { ... } System_variable_tracker::@167

Array

friend System_variable_tracker::Array

m_cache

std::optional<Cache> System_variable_tracker::m_cache

mutableprivate

struct { ... } System_variable_tracker::m_component

m_component_var_cache

sys_var* System_variable_tracker::m_component_var_cache

mutable

m_component_var_name

char System_variable_tracker::m_component_var_name[NAME_LEN+sizeof('.')+NAME_LEN+1]

A dot-separated component-registered variable name.

m_hash_lock_recursion_depth

thread_local int System_variable_tracker::m_hash_lock_recursion_depth {0}

staticprivate

A non-zero value suppresses LOCK_system_variables_hash guards in System_variable_tracker::access_system_variable.

struct { ... } System_variable_tracker::m_keycache

m_keycache_name_size

size_t System_variable_tracker::m_keycache_name_size

m_keycache_var

sys_var* System_variable_tracker::m_keycache_var

m_keycache_var_name

char System_variable_tracker::m_keycache_var_name[NAME_LEN+sizeof(".key_cache_division_limit")]

A dot-separated key cache name or, for a reduced form of key cache variable names, a key cache property name as specified by the caller of System_variable_tracker::make_traker().

struct { ... } System_variable_tracker::m_plugin

m_plugin_var_cache

sys_var* System_variable_tracker::m_plugin_var_cache

mutable

m_plugin_var_name

char System_variable_tracker::m_plugin_var_name[NAME_LEN+1]

A "_"-separated plugin-registered variables name.

struct { ... } System_variable_tracker::m_static

m_static_var

sys_var* System_variable_tracker::m_static_var

m_tag

Lifetime System_variable_tracker::m_tag

private

SYSTEM_VARIABLE_PREALLOC

constexpr size_t System_variable_tracker::SYSTEM_VARIABLE_PREALLOC = 200

staticconstexpr

Number of system variable elements to preallocate.

---

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

• sql/set_var.h
• sql/set_var.cc