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MDEV-6089 - MySQL WL#7305 "Improve MDL scalability by using lock-free hash"

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Simplified MDL_object_lock and MDL_scoped_lock dichotomy so that they can be
stored in LF_HASH. This was done by moving out their differences to a
MDL_lock_strategy structure which is referenced from the MDL_lock object by
pointer.
This commit is contained in:
Sergey Vojtovich 2015-02-26 18:40:05 +04:00
parent f475a7f949
commit f5bd1d0126
1 changed files with 150 additions and 196 deletions
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346
sql/mdl.cc
View file

@ -327,6 +327,101 @@ public:
typedef Ticket_list::List::Iterator Ticket_iterator;
/**
Helper struct which defines how different types of locks are handled
for a specific MDL_lock. In practice we use only two strategies: "scoped"
lock strategy for locks in GLOBAL, COMMIT and SCHEMA namespaces and
"object" lock strategy for all other namespaces.
*/
struct MDL_lock_strategy
{
virtual const bitmap_t *incompatible_granted_types_bitmap() const = 0;
virtual const bitmap_t *incompatible_waiting_types_bitmap() const = 0;
virtual bool needs_notification(const MDL_ticket *ticket) const = 0;
virtual bool conflicting_locks(const MDL_ticket *ticket) const = 0;
virtual bitmap_t hog_lock_types_bitmap() const = 0;
};
/**
An implementation of the scoped metadata lock. The only locking modes
which are supported at the moment are SHARED and INTENTION EXCLUSIVE
and EXCLUSIVE
*/
struct MDL_scoped_lock : public MDL_lock_strategy
{
virtual const bitmap_t *incompatible_granted_types_bitmap() const
{ return m_granted_incompatible; }
virtual const bitmap_t *incompatible_waiting_types_bitmap() const
{ return m_waiting_incompatible; }
virtual bool needs_notification(const MDL_ticket *ticket) const
{ return (ticket->get_type() == MDL_SHARED); }
/**
Notify threads holding scoped IX locks which conflict with a pending
S lock.
Thread which holds global IX lock can be a handler thread for
insert delayed. We need to kill such threads in order to get
global shared lock. We do this my calling code outside of MDL.
*/
virtual bool conflicting_locks(const MDL_ticket *ticket) const
{ return ticket->get_type() == MDL_INTENTION_EXCLUSIVE; }
/*
In scoped locks, only IX lock request would starve because of X/S. But that
is practically very rare case. So just return 0 from this function.
*/
virtual bitmap_t hog_lock_types_bitmap() const
{ return 0; }
private:
static const bitmap_t m_granted_incompatible[MDL_TYPE_END];
static const bitmap_t m_waiting_incompatible[MDL_TYPE_END];
};
/**
An implementation of a per-object lock. Supports SHARED, SHARED_UPGRADABLE,
SHARED HIGH PRIORITY and EXCLUSIVE locks.
*/
struct MDL_object_lock : public MDL_lock_strategy
{
virtual const bitmap_t *incompatible_granted_types_bitmap() const
{ return m_granted_incompatible; }
virtual const bitmap_t *incompatible_waiting_types_bitmap() const
{ return m_waiting_incompatible; }
virtual bool needs_notification(const MDL_ticket *ticket) const
{ return (ticket->get_type() >= MDL_SHARED_NO_WRITE); }
/**
Notify threads holding a shared metadata locks on object which
conflict with a pending X, SNW or SNRW lock.
If thread which holds conflicting lock is waiting on table-level
lock or some other non-MDL resource we might need to wake it up
by calling code outside of MDL.
*/
virtual bool conflicting_locks(const MDL_ticket *ticket) const
{ return ticket->get_type() < MDL_SHARED_UPGRADABLE; }
/*
To prevent starvation, these lock types that are only granted
max_write_lock_count times in a row while other lock types are
waiting.
*/
virtual bitmap_t hog_lock_types_bitmap() const
{
return (MDL_BIT(MDL_SHARED_NO_WRITE) |
MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_EXCLUSIVE));
}
private:
static const bitmap_t m_granted_incompatible[MDL_TYPE_END];
static const bitmap_t m_waiting_incompatible[MDL_TYPE_END];
};
public:
/** The key of the object (data) being protected. */
MDL_key key;
@ -370,16 +465,16 @@ public:
return (m_granted.is_empty() && m_waiting.is_empty());
}
virtual const bitmap_t *incompatible_granted_types_bitmap() const = 0;
virtual const bitmap_t *incompatible_waiting_types_bitmap() const = 0;
const bitmap_t *incompatible_granted_types_bitmap() const
{ return m_strategy->incompatible_granted_types_bitmap(); }
const bitmap_t *incompatible_waiting_types_bitmap() const
{ return m_strategy->incompatible_waiting_types_bitmap(); }
bool has_pending_conflicting_lock(enum_mdl_type type);
bool can_grant_lock(enum_mdl_type type, MDL_context *requstor_ctx,
bool ignore_lock_priority) const;
inline static MDL_lock *create(const MDL_key *key);
inline unsigned long get_lock_owner() const;
void reschedule_waiters();
@ -389,10 +484,28 @@ public:
bool visit_subgraph(MDL_ticket *waiting_ticket,
MDL_wait_for_graph_visitor *gvisitor);
virtual bool needs_notification(const MDL_ticket *ticket) const = 0;
virtual void notify_conflicting_locks(MDL_context *ctx) = 0;
bool needs_notification(const MDL_ticket *ticket) const
{ return m_strategy->needs_notification(ticket); }
void notify_conflicting_locks(MDL_context *ctx)
{
Ticket_iterator it(m_granted);
MDL_ticket *conflicting_ticket;
while ((conflicting_ticket= it++))
{
if (conflicting_ticket->get_ctx() != ctx &&
m_strategy->conflicting_locks(conflicting_ticket))
{
MDL_context *conflicting_ctx= conflicting_ticket->get_ctx();
virtual bitmap_t hog_lock_types_bitmap() const = 0;
ctx->get_owner()->
notify_shared_lock(conflicting_ctx->get_owner(),
conflicting_ctx->get_needs_thr_lock_abort());
}
}
}
bitmap_t hog_lock_types_bitmap() const
{ return m_strategy->hog_lock_types_bitmap(); }
/** List of granted tickets for this lock. */
Ticket_list m_granted;
@ -413,106 +526,37 @@ public:
m_state(0)
{
mysql_prlock_init(key_MDL_lock_rwlock, &m_rwlock);
switch (key_arg->mdl_namespace())
{
case MDL_key::GLOBAL:
case MDL_key::SCHEMA:
case MDL_key::COMMIT:
m_strategy= &m_scoped_lock_strategy;
break;
default:
m_strategy= &m_object_lock_strategy;
}
}
virtual ~MDL_lock()
{
mysql_prlock_destroy(&m_rwlock);
}
inline static void destroy(MDL_lock *lock);
/**
Lock state: first 31 bits are reference counter, 32-nd bit is deleted flag.
*/
static const int32 DELETED= 1 << 31;
int32 m_state;
};
/**
An implementation of the scoped metadata lock. The only locking modes
which are supported at the moment are SHARED and INTENTION EXCLUSIVE
and EXCLUSIVE
*/
class MDL_scoped_lock : public MDL_lock
{
public:
MDL_scoped_lock(const MDL_key *key_arg)
: MDL_lock(key_arg)
{ }
virtual const bitmap_t *incompatible_granted_types_bitmap() const
{
return m_granted_incompatible;
}
virtual const bitmap_t *incompatible_waiting_types_bitmap() const
{
return m_waiting_incompatible;
}
virtual bool needs_notification(const MDL_ticket *ticket) const
{
return (ticket->get_type() == MDL_SHARED);
}
virtual void notify_conflicting_locks(MDL_context *ctx);
/*
In scoped locks, only IX lock request would starve because of X/S. But that
is practically very rare case. So just return 0 from this function.
*/
virtual bitmap_t hog_lock_types_bitmap() const
{
return 0;
}
private:
static const bitmap_t m_granted_incompatible[MDL_TYPE_END];
static const bitmap_t m_waiting_incompatible[MDL_TYPE_END];
const MDL_lock_strategy *m_strategy;
static const MDL_scoped_lock m_scoped_lock_strategy;
static const MDL_object_lock m_object_lock_strategy;
};
/**
An implementation of a per-object lock. Supports SHARED, SHARED_UPGRADABLE,
SHARED HIGH PRIORITY and EXCLUSIVE locks.
*/
class MDL_object_lock : public MDL_lock
{
public:
MDL_object_lock(const MDL_key *key_arg)
: MDL_lock(key_arg)
{ }
virtual const bitmap_t *incompatible_granted_types_bitmap() const
{
return m_granted_incompatible;
}
virtual const bitmap_t *incompatible_waiting_types_bitmap() const
{
return m_waiting_incompatible;
}
virtual bool needs_notification(const MDL_ticket *ticket) const
{
return (ticket->get_type() >= MDL_SHARED_NO_WRITE);
}
virtual void notify_conflicting_locks(MDL_context *ctx);
/*
To prevent starvation, these lock types that are only granted
max_write_lock_count times in a row while other lock types are
waiting.
*/
virtual bitmap_t hog_lock_types_bitmap() const
{
return (MDL_BIT(MDL_SHARED_NO_WRITE) |
MDL_BIT(MDL_SHARED_NO_READ_WRITE) |
MDL_BIT(MDL_EXCLUSIVE));
}
private:
static const bitmap_t m_granted_incompatible[MDL_TYPE_END];
static const bitmap_t m_waiting_incompatible[MDL_TYPE_END];
};
const MDL_lock::MDL_scoped_lock MDL_lock::m_scoped_lock_strategy;
const MDL_lock::MDL_object_lock MDL_lock::m_object_lock_strategy;
static MDL_map mdl_locks;
@ -627,7 +671,7 @@ int mdl_iterate(int (*callback)(MDL_ticket *ticket, void *arg), void *arg)
mysql_prlock_unlock(&lock->m_rwlock);
if (unlikely(old_state == MDL_lock::DELETED + 1))
MDL_lock::destroy(lock);
delete lock;
}
end:
delete_dynamic(&locks);
@ -650,8 +694,8 @@ void MDL_map::init()
MDL_key global_lock_key(MDL_key::GLOBAL, "", "");
MDL_key commit_lock_key(MDL_key::COMMIT, "", "");
m_global_lock= MDL_lock::create(&global_lock_key);
m_commit_lock= MDL_lock::create(&commit_lock_key);
m_global_lock= new (std::nothrow) MDL_lock(&global_lock_key);
m_commit_lock= new (std::nothrow) MDL_lock(&commit_lock_key);
mysql_mutex_init(key_MDL_map_mutex, &m_mutex, NULL);
my_hash_init2(&m_locks, 0, &my_charset_bin, 16 /* FIXME */, 0, 0,
@ -666,8 +710,8 @@ void MDL_map::init()
void MDL_map::destroy()
{
MDL_lock::destroy(m_global_lock);
MDL_lock::destroy(m_commit_lock);
delete m_global_lock;
delete m_commit_lock;
DBUG_ASSERT(!m_locks.records);
mysql_mutex_destroy(&m_mutex);
@ -718,10 +762,10 @@ retry:
mdl_key->length())))
{
/* No lock object found so we need to create a new one. */
lock= MDL_lock::create(mdl_key);
lock= new (std::nothrow) MDL_lock(mdl_key);
if (!lock || my_hash_insert(&m_locks, (uchar*)lock))
{
MDL_lock::destroy(lock);
delete lock;
mysql_mutex_unlock(&m_mutex);
return NULL;
}
@ -765,7 +809,7 @@ bool MDL_map::move_from_hash_to_lock_mutex(MDL_lock *lock)
*/
mysql_prlock_unlock(&lock->m_rwlock);
if (old_state == MDL_lock::DELETED + 1)
MDL_lock::destroy(lock);
delete lock;
return TRUE;
}
return FALSE;
@ -838,7 +882,7 @@ void MDL_map::remove(MDL_lock *lock)
mysql_mutex_unlock(&m_mutex);
mysql_prlock_unlock(&lock->m_rwlock);
if (!old_state)
MDL_lock::destroy(lock);
delete lock;
}
@ -933,32 +977,6 @@ void MDL_request::init(const MDL_key *key_arg,
}
/**
Auxiliary functions needed for creation/destruction of MDL_lock objects.
@note Also chooses an MDL_lock descendant appropriate for object namespace.
*/
inline MDL_lock *MDL_lock::create(const MDL_key *mdl_key)
{
switch (mdl_key->mdl_namespace())
{
case MDL_key::GLOBAL:
case MDL_key::SCHEMA:
case MDL_key::COMMIT:
return new (std::nothrow) MDL_scoped_lock(mdl_key);
default:
return new (std::nothrow) MDL_object_lock(mdl_key);
}
}
void MDL_lock::destroy(MDL_lock *lock)
{
delete lock;
}
/**
Auxiliary functions needed for creation/destruction of MDL_ticket
objects.
@ -1417,14 +1435,16 @@ void MDL_lock::reschedule_waiters()
on schema objects) and aren't acquired for DML.
*/
const MDL_lock::bitmap_t MDL_scoped_lock::m_granted_incompatible[MDL_TYPE_END] =
const MDL_lock::bitmap_t
MDL_lock::MDL_scoped_lock::m_granted_incompatible[MDL_TYPE_END]=
{
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED),
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_INTENTION_EXCLUSIVE), 0, 0, 0, 0, 0, 0,
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED) | MDL_BIT(MDL_INTENTION_EXCLUSIVE)
};
const MDL_lock::bitmap_t MDL_scoped_lock::m_waiting_incompatible[MDL_TYPE_END] =
const MDL_lock::bitmap_t
MDL_lock::MDL_scoped_lock::m_waiting_incompatible[MDL_TYPE_END]=
{
MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED),
MDL_BIT(MDL_EXCLUSIVE), 0, 0, 0, 0, 0, 0, 0
@ -1486,7 +1506,7 @@ const MDL_lock::bitmap_t MDL_scoped_lock::m_waiting_incompatible[MDL_TYPE_END] =
*/
const MDL_lock::bitmap_t
MDL_object_lock::m_granted_incompatible[MDL_TYPE_END] =
MDL_lock::MDL_object_lock::m_granted_incompatible[MDL_TYPE_END]=
{
0,
MDL_BIT(MDL_EXCLUSIVE),
@ -1510,7 +1530,7 @@ MDL_object_lock::m_granted_incompatible[MDL_TYPE_END] =
const MDL_lock::bitmap_t
MDL_object_lock::m_waiting_incompatible[MDL_TYPE_END] =
MDL_lock::MDL_object_lock::m_waiting_incompatible[MDL_TYPE_END]=
{
0,
MDL_BIT(MDL_EXCLUSIVE),
@ -1972,72 +1992,6 @@ MDL_context::clone_ticket(MDL_request *mdl_request)
}
/**
Notify threads holding a shared metadata locks on object which
conflict with a pending X, SNW or SNRW lock.
@param ctx MDL_context for current thread.
*/
void MDL_object_lock::notify_conflicting_locks(MDL_context *ctx)
{
Ticket_iterator it(m_granted);
MDL_ticket *conflicting_ticket;
while ((conflicting_ticket= it++))
{
/* Only try to abort locks on which we back off. */
if (conflicting_ticket->get_ctx() != ctx &&
conflicting_ticket->get_type() < MDL_SHARED_UPGRADABLE)
{
MDL_context *conflicting_ctx= conflicting_ticket->get_ctx();
/*
If thread which holds conflicting lock is waiting on table-level
lock or some other non-MDL resource we might need to wake it up
by calling code outside of MDL.
*/
ctx->get_owner()->
notify_shared_lock(conflicting_ctx->get_owner(),
conflicting_ctx->get_needs_thr_lock_abort());
}
}
}
/**
Notify threads holding scoped IX locks which conflict with a pending S lock.
@param ctx MDL_context for current thread.
*/
void MDL_scoped_lock::notify_conflicting_locks(MDL_context *ctx)
{
Ticket_iterator it(m_granted);
MDL_ticket *conflicting_ticket;
while ((conflicting_ticket= it++))
{
if (conflicting_ticket->get_ctx() != ctx &&
conflicting_ticket->get_type() == MDL_INTENTION_EXCLUSIVE)
{
MDL_context *conflicting_ctx= conflicting_ticket->get_ctx();
/*
Thread which holds global IX lock can be a handler thread for
insert delayed. We need to kill such threads in order to get
global shared lock. We do this my calling code outside of MDL.
*/
ctx->get_owner()->
notify_shared_lock(conflicting_ctx->get_owner(),
conflicting_ctx->get_needs_thr_lock_abort());
}
}
}
/**
Acquire one lock with waiting for conflicting locks to go away if needed.