Deadlock_detection_visitor Class Reference

A context of the recursive traversal through all contexts in all sessions in search for deadlock. More...

Inheritance diagram for Deadlock_detection_visitor:

Public Member Functions
	Deadlock_detection_visitor (MDL_context *start_node_arg)
bool	enter_node (MDL_context *node) override
	Enter a node of a wait-for graph. More...
void	leave_node (MDL_context *node) override
	Done inspecting this node. More...
bool	inspect_edge (MDL_context *dest) override
	Inspect a wait-for graph edge from one MDL context to another. More...
MDL_context *	get_victim () const
Public Member Functions inherited from MDL_wait_for_graph_visitor
virtual	~MDL_wait_for_graph_visitor ()
	MDL_wait_for_graph_visitor ()

Private Member Functions
void	opt_change_victim_to (MDL_context *new_victim)
	Change the deadlock victim to a new one if it has lower deadlock weight. More...

Private Attributes
MDL_context *	m_start_node
	The context which has initiated the search. More...
MDL_context *	m_victim
	If a deadlock is found, the context that identifies the victim. More...
uint	m_current_search_depth
	Set to the 0 at start. More...
bool	m_found_deadlock
	true if we found a deadlock. More...

Static Private Attributes
static const uint	MAX_SEARCH_DEPTH = 32
	Maximum depth for deadlock searches. More...

Additional Inherited Members
Public Attributes inherited from MDL_wait_for_graph_visitor
uint	m_lock_open_count
	XXX, hack: During deadlock search, we may need to inspect TABLE_SHAREs and acquire LOCK_open. More...

Detailed Description

A context of the recursive traversal through all contexts in all sessions in search for deadlock.

Constructor & Destructor Documentation

Deadlock_detection_visitor()

Deadlock_detection_visitor::Deadlock_detection_visitor ( MDL_context *  start_node_arg )

inline

Member Function Documentation

enter_node()

bool Deadlock_detection_visitor::enter_node ( MDL_context *  node )

overridevirtual

Enter a node of a wait-for graph.

After a node is entered, inspect_edge() will be called for all wait-for destinations of this node. Then leave_node() will be called. We call "enter_node()" for all nodes we inspect, including the starting node.

Return values

true	Maximum search depth exceeded.
false	OK.

Implements MDL_wait_for_graph_visitor.

get_victim()

MDL_context * Deadlock_detection_visitor::get_victim ( ) const

inline

inspect_edge()

bool Deadlock_detection_visitor::inspect_edge ( MDL_context *  node )

overridevirtual

Inspect a wait-for graph edge from one MDL context to another.

Return values

true	A loop is found.
false	No loop is found.

Implements MDL_wait_for_graph_visitor.

leave_node()

void Deadlock_detection_visitor::leave_node ( MDL_context *  node )

overridevirtual

Done inspecting this node.

Decrease the search depth. If a deadlock is found, and we are backtracking to the start node, optionally change the deadlock victim to one with lower deadlock weight.

Implements MDL_wait_for_graph_visitor.

opt_change_victim_to()

void Deadlock_detection_visitor::opt_change_victim_to ( MDL_context *  new_victim )

private

Change the deadlock victim to a new one if it has lower deadlock weight.

Parameters

new_victim

New candidate for deadlock victim.

Member Data Documentation

m_current_search_depth

uint Deadlock_detection_visitor::m_current_search_depth

private

Set to the 0 at start.

Increased whenever we descend into another MDL context (aka traverse to the next wait-for graph node). When MAX_SEARCH_DEPTH is reached, we assume that a deadlock is found, even if we have not found a loop.

m_found_deadlock

bool Deadlock_detection_visitor::m_found_deadlock

private

true if we found a deadlock.

m_start_node

MDL_context* Deadlock_detection_visitor::m_start_node

private

The context which has initiated the search.

There can be multiple searches happening in parallel at the same time.

m_victim

MDL_context* Deadlock_detection_visitor::m_victim

private

If a deadlock is found, the context that identifies the victim.

MAX_SEARCH_DEPTH

const uint Deadlock_detection_visitor::MAX_SEARCH_DEPTH = 32

staticprivate

Maximum depth for deadlock searches.

After this depth is achieved we will unconditionally declare that there is a deadlock.

Note

This depth should be small enough to avoid stack being exhausted by recursive search algorithm.

TODO: Find out what is the optimal value for this parameter. Current value is safe, but probably sub-optimal, as there is an anecdotal evidence that real-life deadlocks are even shorter typically.

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

• sql/mdl.cc