Mts_submode_logical_clock Class Reference

Parallelization using Master parallelization information For significance of each method check definition of Mts_submode. More...

#include <rpl_mta_submode.h>

Inheritance diagram for Mts_submode_logical_clock:

Public Member Functions
	Mts_submode_logical_clock ()
int	schedule_next_event (Relay_log_info *rli, Log_event *ev) override
	Does necessary arrangement before scheduling next event. More...
void	attach_temp_tables (THD *thd, const Relay_log_info *rli, Query_log_event *ev) override
	Logic to attach the temporary tables from the worker threads upon event execution. More...
void	detach_temp_tables (THD *thd, const Relay_log_info *rli, Query_log_event *) override
	Logic to detach the temporary tables from the worker threads upon event execution. More...
Slave_worker *	get_least_occupied_worker (Relay_log_info *rli, Slave_worker_array *ws, Log_event *ev) override
	Logic to get least occupied worker when the sql mts_submode= master_parallel. More...
void	start_new_group ()
void	withdraw_delegated_job ()
	Withdraw the delegated_job increased by the group. More...
int	wait_for_workers_to_finish (Relay_log_info *rli, Slave_worker *ignore=nullptr) override
	Waits for slave workers to finish off the pending tasks before returning. More...
bool	wait_for_last_committed_trx (Relay_log_info *rli, longlong last_committed_arg)
	The method implements logical timestamp conflict detection and resolution through waiting by the calling thread. More...
longlong	get_lwm_timestamp (Relay_log_info *rli, bool need_lock)
	The method finds the minimum logical timestamp (low-water-mark) of committed transactions. More...
longlong	estimate_lwm_timestamp ()
	~Mts_submode_logical_clock () override=default
Public Member Functions inherited from Mts_submode
	Mts_submode ()=default
enum_mts_parallel_type	get_type ()
virtual bool	set_multi_threaded_applier_context (const Relay_log_info &, Log_event &)
	Sets additional context before the event is set to execute. More...
virtual	~Mts_submode ()=default

Static Public Member Functions
static bool	clock_leq (longlong a, longlong b)

Public Attributes
uint	jobs_done
bool	is_error
std::atomic< longlong >	min_waited_timestamp

Static Public Attributes
static const ulong	INDEX_UNDEF = (ulong)-1

Protected Member Functions
std::pair< uint, my_thread_id >	get_server_and_thread_id (TABLE *table)
	Protected method to fetch the server_id and pseudo_thread_id from a temporary table. More...
Slave_worker *	get_free_worker (Relay_log_info *rli)
	Protected method to fetch a worker having no events assigned. More...

Private Attributes
bool	first_event
bool	force_new_group
bool	is_new_group
uint	delegated_jobs
std::atomic< longlong >	last_lwm_timestamp
ulong	last_lwm_index
longlong	last_committed
longlong	sequence_number

Additional Inherited Members
Protected Attributes inherited from Mts_submode
enum_mts_parallel_type	type

Detailed Description

Parallelization using Master parallelization information For significance of each method check definition of Mts_submode.

Constructor & Destructor Documentation

Mts_submode_logical_clock()

Mts_submode_logical_clock::Mts_submode_logical_clock

(

)

~Mts_submode_logical_clock()

Mts_submode_logical_clock::~Mts_submode_logical_clock ( )

overridedefault

Member Function Documentation

attach_temp_tables()

void Mts_submode_logical_clock::attach_temp_tables ( THD *  thd, const Relay_log_info *  rli, Query_log_event *  ev  )

overridevirtual

Logic to attach the temporary tables from the worker threads upon event execution.

Parameters

thd	THD instance
rli	Relay_log_info instance
ev	Query_log_event that is being applied

Implements Mts_submode.

clock_leq()

static bool Mts_submode_logical_clock::clock_leq ( longlong  a, longlong  b  )

inlinestatic

detach_temp_tables()

void Mts_submode_logical_clock::detach_temp_tables ( THD *  thd, const Relay_log_info *  rli, Query_log_event *    )

overridevirtual

Logic to detach the temporary tables from the worker threads upon event execution.

Parameters

thd	THD instance
rli	Relay_log_info instance

Implements Mts_submode.

estimate_lwm_timestamp()

longlong Mts_submode_logical_clock::estimate_lwm_timestamp ( )

inline

get_free_worker()

Slave_worker * Mts_submode_logical_clock::get_free_worker ( Relay_log_info *  rli )

protected

Protected method to fetch a worker having no events assigned.

The method is supposed to be called by Coordinator, therefore comparison like w_i->jobs.len == 0 must (eventually) succeed.

todo: consider to optimize scan that is getting more expensive with more # of Workers.

Returns

a pointer to Worker or NULL if none is free.

get_least_occupied_worker()

Slave_worker * Mts_submode_logical_clock::get_least_occupied_worker ( Relay_log_info *  rli, Slave_worker_array *  ws, Log_event *  ev  )

overridevirtual

Logic to get least occupied worker when the sql mts_submode= master_parallel.

Parameters

rli	relay log info of coordinator
ws	array of worker threads
ev	event for which we are searching for a worker.

Returns

slave worker thread or NULL when coordinator is killed by any worker.

Implements Mts_submode.

get_lwm_timestamp()

longlong Mts_submode_logical_clock::get_lwm_timestamp	(	Relay_log_info *	rli,
		bool	need_lock
	)

The method finds the minimum logical timestamp (low-water-mark) of committed transactions.

The successful search results in a pair of a logical timestamp value and a GAQ index that contains it. last_lwm_timestamp may still be raised though the search does not find any satisfying running index. Search is implemented as headway scanning of GAQ from a point of a previous search's stop position (last_lwm_index). Whether the cached (memorized) index value is considered to be stale when its timestamp gets less than the current "stable" LWM:

 last_lwm_timestamp <= GAQ.lwm.sequence_number           (*)

Staleness is caused by GAQ garbage collection that increments the rhs of (*), see move_queue_head(). When that's diagnosed, the search in GAQ needs restarting from the queue tail.

Formally, the undefined cached value of last_lwm_timestamp is also stale.

           the last time index containing lwm
               +------+
               | LWM  |
               |  |   |
               V  V   V
GAQ:   xoooooxxxxxXXXXX...X
             ^   ^
             |   | LWM+1
             |
             +- tne new current_lwm

      <---- logical (commit) time ----

here ‘x’ stands for committed, ‘X’ for committed and discarded from the running range of the queue, ‘o’ for not committed.

Parameters

rli	Relay_log_info pointer
need_lock	Either the caller or the function must hold a mutex to avoid race with concurrent GAQ update.

Returns

possibly updated current_lwm

get_server_and_thread_id()

std::pair< uint, my_thread_id > Mts_submode_logical_clock::get_server_and_thread_id ( TABLE *  table )

protected

Protected method to fetch the server_id and pseudo_thread_id from a temporary table.

Parameters

table

instance pointer of TABLE structure.

Returns

std:pair<uint, my_thread_id>

Note

It is the caller's responsibility to make sure we call this function only for temp tables.

schedule_next_event()

int Mts_submode_logical_clock::schedule_next_event ( Relay_log_info *  rli, Log_event *  ev  )

overridevirtual

Does necessary arrangement before scheduling next event.

The method computes the meta-group status of the being scheduled transaction represented by the event argument. When the status is found OUT (of the current meta-group) as encoded as is_new_group == true the global Scheduler (Coordinator thread) requests full synchronization with all Workers. The current being assigned group descriptor gets associated with the group's logical timestamp aka sequence_number.

Returns

ER_MTA_CANT_PARALLEL, ER_MTA_INCONSISTENT_DATA 0 if no error or slave has been killed gracefully

Implements Mts_submode.

start_new_group()

void Mts_submode_logical_clock::start_new_group ( )

inline

wait_for_last_committed_trx()

bool Mts_submode_logical_clock::wait_for_last_committed_trx	(	Relay_log_info *	rli,
		longlong	last_committed_arg
	)

The method implements logical timestamp conflict detection and resolution through waiting by the calling thread.

The conflict or waiting condition is like the following

    lwm < last_committed,

where lwm is a minimum logical timestamp of committed transactions. Since the lwm's exact value is not always available its pessimistic estimate (an old version) is improved (get_lwm_timestamp()) as the first step before to the actual waiting commitment.

Special cases include:

When last_committed_arg is uninitialized the calling thread must proceed without waiting for anyone. Any possible dependency with unknown commit parent transaction shall be sorted out by the parent;

When the gaq index is subsequent to the last lwm index there's no dependency of the current transaction with any regardless of lwm timestamp should it be SEQ_UNINIT. Consequently when GAQ consists of just one item there's none to wait. Such latter case is left to the caller to handle.

Note

The caller must make sure the current transaction won't be waiting for itself. That is the method should not be caller by a Worker whose group assignment is in the GAQ front item.

Parameters

rli	relay log info of coordinator
last_committed_arg	logical timestamp of a parent transaction

Returns

false as success, true when the error flag is raised or the caller thread is found killed.

wait_for_workers_to_finish()

int Mts_submode_logical_clock::wait_for_workers_to_finish ( Relay_log_info *  rli, Slave_worker *  ignore = nullptr  )

overridevirtual

Waits for slave workers to finish off the pending tasks before returning.

Used in this submode to make sure that all assigned jobs have been done.

Parameters

rli	coordinator rli.
ignore	worker to ignore.

Returns

-1 for error. 0 no error.

Implements Mts_submode.

withdraw_delegated_job()

void Mts_submode_logical_clock::withdraw_delegated_job ( )

inline

Withdraw the delegated_job increased by the group.

Member Data Documentation

delegated_jobs

uint Mts_submode_logical_clock::delegated_jobs

private

first_event

bool Mts_submode_logical_clock::first_event

private

force_new_group

bool Mts_submode_logical_clock::force_new_group

private

INDEX_UNDEF

const ulong Mts_submode_logical_clock::INDEX_UNDEF = (ulong)-1

static

is_error

bool Mts_submode_logical_clock::is_error

is_new_group

bool Mts_submode_logical_clock::is_new_group

private

jobs_done

uint Mts_submode_logical_clock::jobs_done

last_committed

longlong Mts_submode_logical_clock::last_committed

private

last_lwm_index

ulong Mts_submode_logical_clock::last_lwm_index

private

last_lwm_timestamp

std::atomic<longlong> Mts_submode_logical_clock::last_lwm_timestamp

private

min_waited_timestamp

std::atomic<longlong> Mts_submode_logical_clock::min_waited_timestamp

sequence_number

longlong Mts_submode_logical_clock::sequence_number

private

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

• sql/rpl_mta_submode.h
• sql/rpl_mta_submode.cc