Rpl_transaction_write_set_ctx Class Reference

Thread class responsible for the collection of write sets associated to a transaction. More...

#include <rpl_transaction_write_set_ctx.h>

Public Member Functions
	Rpl_transaction_write_set_ctx ()
virtual	~Rpl_transaction_write_set_ctx ()=default
bool	add_write_set (uint64 hash)
	Function to add the write set of the hash of the PKE in the std::vector in the transaction_ctx object. More...
std::vector< uint64 > *	get_write_set ()
void	reset_state ()
	Reset the object so it can be used for a new transaction. More...
void	set_has_missing_keys ()
bool	get_has_missing_keys ()
void	set_has_related_foreign_keys ()
bool	get_has_related_foreign_keys ()
bool	was_write_set_limit_reached ()
	Identifies situations where the limit for number of write set entries already exceeded the configure limit. More...
size_t	write_set_memory_size ()
void	add_savepoint (char *name)
	Function to add a new SAVEPOINT identifier in the savepoint map in the transaction_ctx object. More...
void	del_savepoint (char *name)
	Function to delete a SAVEPOINT identifier in the savepoint map in the transaction_ctx object. More...
void	rollback_to_savepoint (char *name)
	Function to delete all data added to write set and savepoint since SAVEPOINT identifier was added to savepoinbt in the transaction_ctx object. More...
void	reset_savepoint_list ()
	Function to push savepoint data to a list and clear the savepoint map in order to create another identifier context, needed on functions ant trigger. More...
void	restore_savepoint_list ()
	Restore previous savepoint map context, called after executed trigger or function. More...
void	set_local_ignore_write_set_memory_limit (bool ignore_limit)
	Set if the thread shall ignore any configured memory limit for write set collection. More...
void	set_local_allow_drop_write_set (bool allow_drop_write_set)
	Set if the thread shall if needed discard write sets. More...

Static Public Member Functions
static void	set_global_write_set_memory_size_limit (uint64 limit)
	Adds a memory limit for write sets. More...
static void	update_global_write_set_memory_size_limit (uint64 limit)
	Updates the memory limit for write sets. More...
static void	set_global_require_full_write_set (bool requires_ws)
	Prevent or allow this class to discard writesets exceeding a size limit If true, a transaction will never discard its write sets. More...

Private Member Functions
void	clear_write_set ()

Private Attributes
std::vector< uint64 >	write_set
bool	m_has_missing_keys
bool	m_has_related_foreign_keys
std::map< std::string, size_t >	savepoint
	Contains information related to SAVEPOINTs. More...
std::list< std::map< std::string, size_t > >	savepoint_list
	Create a savepoint context hierarchy to support encapsulation of identifier name when function or trigger are executed. More...
bool	m_ignore_write_set_memory_limit
	If the thread should or not ignore the set limit for write set collection. More...
bool	m_local_allow_drop_write_set
	Even if a component says all transactions require write sets, this variable says this thread should discard them when they are bigger than m_opt_max_history_size. More...
bool	m_local_has_reached_write_set_limit
	True if the write set size is over the configure limit. More...

Static Private Attributes
static std::atomic< bool >	m_global_component_requires_write_sets
	There is a component requiring write sets on transactions. More...
static std::atomic< uint64 >	m_global_write_set_memory_size_limit
	Memory size limit enforced for write set collection. More...

Detailed Description

Thread class responsible for the collection of write sets associated to a transaction.

It also includes support for save points where information will be discarded on rollbacks to a savepoint.

Write set and flags are reset on Rpl_transaction_write_set_ctx::reset_state().

The write set collection by an executing transaction is capped to a limit. The limit can be "soft" or "hard":

• when a writeset grows above a "soft" limit, the transaction is allowed to execute and commit, but the write set is discarded, and the transaction declared to not have a usable write set.
• when a write set grows above a "hard" limit, the transaction is forced to abort and rollback.

We cannot use a soft limit for transactions that will be certified in GR, since a writeset is required for correct certification. But when GR is disabled, we can use a soft limit, because the writeset is only used to compute transaction dependencies, and we can pessimistically mark the transaction as conflicting with all other transcations when the writeset is discarded. A soft limit can also be used for transactions executed by the GR recovery channel, since they will not be certified, and the GR applier channel, since those transactions have already passed the certification stage.

For the soft limit, we use

• binlog_transaction_dependency_history_size. Transactions bigger than that cannot be added to the writeset history since they do not fit, and therefore are marked as conflicting with all subsequent* transactions anyways. Therefore much of the parallelization for the transaction is already destroyed, and it is unlikely that also marking it as conflicting with previous* transactions makes a significant difference.

For the hard limit, when using Group Replication, we use

• group_replication_transaction_size_limit. Since the writeset is a subset of the transaction, and the transaction is limited to this size anyways, a transaction whose writeset exceeds this limit will fail anyways. So failing it when generating the writeset is merely a fail-fast mechanism, and it is not a restriction to apply this limit to the writeset of all transactions for which the full transaction data is also subject to the limit. The transactions that are subject to this limit are exactly those executed when GR is enabled, except by the GR applier channel and GR recovery channel.

We expose the following interfaces so that components such as GR can control the limit. There is an interface to globally disable/enable the soft limit: static void set_global_require_full_write_set(bool requires_ws); set/alter/remove a hard limit: static void set_global_write_set_memory_size_limit(uint64 limit) static void update_global_write_set_memory_size_limit(uint64 limit);

There is another interface to override the global limits for a thread: void set_local_ignore_write_set_memory_limit(bool ignore_limit); void set_local_allow_drop_write_set(bool allow_drop_write_set);

The local methods are used for example for Group Replication applier and recovery threads as group_replication_transaction_size_limit only applies to client sessions and non group replication replica threads.

Constructor & Destructor Documentation

Rpl_transaction_write_set_ctx()

Rpl_transaction_write_set_ctx::Rpl_transaction_write_set_ctx

(

)

~Rpl_transaction_write_set_ctx()

virtual Rpl_transaction_write_set_ctx::~Rpl_transaction_write_set_ctx ( )

virtualdefault

Member Function Documentation

add_savepoint()

void Rpl_transaction_write_set_ctx::add_savepoint

(

char *

name

)

Function to add a new SAVEPOINT identifier in the savepoint map in the transaction_ctx object.

Parameters

[in]

name

- the identifier name of the SAVEPOINT.

add_write_set()

bool Rpl_transaction_write_set_ctx::add_write_set

(

uint64

hash

)

Function to add the write set of the hash of the PKE in the std::vector in the transaction_ctx object.

Parameters

[in]

hash

- the uint64 type hash value of the PKE.

Returns

true if it can't add the write set entry, false if successful

clear_write_set()

void Rpl_transaction_write_set_ctx::clear_write_set ( )

private

del_savepoint()

void Rpl_transaction_write_set_ctx::del_savepoint

(

char *

name

)

Function to delete a SAVEPOINT identifier in the savepoint map in the transaction_ctx object.

Parameters

[in]

name

- the identifier name of the SAVEPOINT.

get_has_missing_keys()

bool Rpl_transaction_write_set_ctx::get_has_missing_keys

(

)

get_has_related_foreign_keys()

bool Rpl_transaction_write_set_ctx::get_has_related_foreign_keys

(

)

get_write_set()

std::vector< uint64 > * Rpl_transaction_write_set_ctx::get_write_set

(

)

reset_savepoint_list()

void Rpl_transaction_write_set_ctx::reset_savepoint_list

(

)

Function to push savepoint data to a list and clear the savepoint map in order to create another identifier context, needed on functions ant trigger.

reset_state()

void Rpl_transaction_write_set_ctx::reset_state

(

)

Reset the object so it can be used for a new transaction.

restore_savepoint_list()

void Rpl_transaction_write_set_ctx::restore_savepoint_list

(

)

Restore previous savepoint map context, called after executed trigger or function.

rollback_to_savepoint()

void Rpl_transaction_write_set_ctx::rollback_to_savepoint

(

char *

name

)

Function to delete all data added to write set and savepoint since SAVEPOINT identifier was added to savepoinbt in the transaction_ctx object.

Parameters

[in]

name

- the identifier name of the SAVEPOINT.

set_global_require_full_write_set()

void Rpl_transaction_write_set_ctx::set_global_require_full_write_set ( bool  requires_ws )

static

Prevent or allow this class to discard writesets exceeding a size limit If true, a transaction will never discard its write sets.

Parameters

requires_ws

if who invoked the method needs or not write sets

set_global_write_set_memory_size_limit()

void Rpl_transaction_write_set_ctx::set_global_write_set_memory_size_limit ( uint64  limit )

static

Adds a memory limit for write sets.

Note

currently only one component can set this limit a time.

Parameters

limit

the limit to be added

set_has_missing_keys()

void Rpl_transaction_write_set_ctx::set_has_missing_keys

(

)

set_has_related_foreign_keys()

void Rpl_transaction_write_set_ctx::set_has_related_foreign_keys

(

)

set_local_allow_drop_write_set()

void Rpl_transaction_write_set_ctx::set_local_allow_drop_write_set

(

bool

allow_drop_write_set

)

Set if the thread shall if needed discard write sets.

Parameters

allow_drop_write_set

if full write sets are not critical

set_local_ignore_write_set_memory_limit()

void Rpl_transaction_write_set_ctx::set_local_ignore_write_set_memory_limit

(

bool

ignore_limit

)

Set if the thread shall ignore any configured memory limit for write set collection.

Parameters

ignore_limit

if the limit should be ignored

update_global_write_set_memory_size_limit()

void Rpl_transaction_write_set_ctx::update_global_write_set_memory_size_limit ( uint64  limit )

static

Updates the memory limit for write sets.

Note

Using the value 0 disables the limit

Parameters

limit

the limit to be added

was_write_set_limit_reached()

bool Rpl_transaction_write_set_ctx::was_write_set_limit_reached

(

)

Identifies situations where the limit for number of write set entries already exceeded the configure limit.

Return values

true	if too many write set entries exist, false otherwise

write_set_memory_size()

size_t Rpl_transaction_write_set_ctx::write_set_memory_size

(

)

Returns

the size of the write_set field in bytes

Member Data Documentation

m_global_component_requires_write_sets

std::atomic< bool > Rpl_transaction_write_set_ctx::m_global_component_requires_write_sets

staticprivate

There is a component requiring write sets on transactions.

m_global_write_set_memory_size_limit

std::atomic< uint64 > Rpl_transaction_write_set_ctx::m_global_write_set_memory_size_limit

staticprivate

Memory size limit enforced for write set collection.

m_has_missing_keys

bool Rpl_transaction_write_set_ctx::m_has_missing_keys

private

m_has_related_foreign_keys

bool Rpl_transaction_write_set_ctx::m_has_related_foreign_keys

private

m_ignore_write_set_memory_limit

bool Rpl_transaction_write_set_ctx::m_ignore_write_set_memory_limit

private

If the thread should or not ignore the set limit for write set collection.

m_local_allow_drop_write_set

bool Rpl_transaction_write_set_ctx::m_local_allow_drop_write_set

private

Even if a component says all transactions require write sets, this variable says this thread should discard them when they are bigger than m_opt_max_history_size.

m_local_has_reached_write_set_limit

bool Rpl_transaction_write_set_ctx::m_local_has_reached_write_set_limit

private

True if the write set size is over the configure limit.

savepoint

std::map<std::string, size_t> Rpl_transaction_write_set_ctx::savepoint

private

Contains information related to SAVEPOINTs.

The key on map is the identifier and the value is the size of write set when command was executed.

savepoint_list

std::list<std::map<std::string, size_t> > Rpl_transaction_write_set_ctx::savepoint_list

private

Create a savepoint context hierarchy to support encapsulation of identifier name when function or trigger are executed.

write_set

std::vector<uint64> Rpl_transaction_write_set_ctx::write_set

private

---

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

• sql/rpl_transaction_write_set_ctx.h
• sql/rpl_transaction_write_set_ctx.cc