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Patch that changes metadata locking subsystem to use mutex per lock and

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condition variable per context instead of one mutex and one conditional
variable for the whole subsystem.

This should increase concurrency in this subsystem.

It also opens the way for further changes which are necessary to solve
such bugs as bug #46272 "MySQL 5.4.4, new MDL: unnecessary deadlock"
and bug #37346 "innodb does not detect deadlock between update and alter
table".

Two other notable changes done by this patch:

- MDL subsystem no longer implicitly acquires global intention exclusive
  metadata lock when per-object metadata lock is acquired. Now this has
  to be done by explicit calls outside of MDL subsystem.
- Instead of using separate MDL_context for opening system tables/tables
  for purposes of I_S we now create MDL savepoint in the main context
  before opening tables and rollback to this savepoint after closing
  them. This means that it is now possible to get ER_LOCK_DEADLOCK error
  even not inside a transaction. This might happen in unlikely case when
  one runs DDL on one of system tables while also running DDL on some
  other tables. Cases when this ER_LOCK_DEADLOCK error is not justified
  will be addressed by advanced deadlock detector for MDL subsystem which
  we plan to implement.
This commit is contained in:
Dmitry Lenev
2010-01-21 23:43:03 +03:00
parent c005126107
commit a63f8480db
24 changed files with 1595 additions and 848 deletions
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200
sql/sql_base.cc
View File

@ -1519,25 +1519,23 @@ void close_thread_tables(THD *thd)
if (thd->open_tables)
close_open_tables(thd);
if (thd->state_flags & Open_tables_state::BACKUPS_AVAIL)
/*
- If inside a multi-statement transaction,
defer the release of metadata locks until the current
transaction is either committed or rolled back. This prevents
other statements from modifying the table for the entire
duration of this transaction. This provides commit ordering
and guarantees serializability across multiple transactions.
- If closing a system table, defer the release of metadata locks
to the caller. We have no sentinel in MDL subsystem to guard
transactional locks from system tables locks, so don't know
which locks are which here.
- If in autocommit mode, or outside a transactional context,
automatically release metadata locks of the current statement.
*/
if (! thd->in_multi_stmt_transaction() &&
! (thd->state_flags & Open_tables_state::BACKUPS_AVAIL))
{
/* We can't have an open HANDLER in the backup open tables state. */
DBUG_ASSERT(thd->mdl_context.lt_or_ha_sentinel() == NULL);
/*
Due to the above assert, this is guaranteed to release *all* locks
in the context.
*/
thd->mdl_context.release_transactional_locks();
}
else if (! thd->in_multi_stmt_transaction())
{
/*
Defer the release of metadata locks until the current transaction
is either committed or rolled back. This prevents other statements
from modifying the table for the entire duration of this transaction.
This provides commitment ordering for guaranteeing serializability
across multiple transactions.
*/
thd->mdl_context.release_transactional_locks();
}
@ -2336,10 +2334,9 @@ open_table_get_mdl_lock(THD *thd, TABLE_LIST *table_list,
Open_table_context *ot_ctx,
uint flags)
{
ot_ctx->add_request(mdl_request);
if (table_list->lock_strategy)
{
MDL_request *global_request;
/*
In case of CREATE TABLE .. If NOT EXISTS .. SELECT, the table
may not yet exist. Let's acquire an exclusive lock for that
@ -2349,10 +2346,24 @@ open_table_get_mdl_lock(THD *thd, TABLE_LIST *table_list,
shared locks. This invariant is preserved here and is also
enforced by asserts in metadata locking subsystem.
*/
mdl_request->set_type(MDL_EXCLUSIVE);
DBUG_ASSERT(! thd->mdl_context.has_locks() ||
thd->handler_tables_hash.records);
thd->handler_tables_hash.records ||
thd->global_read_lock);
if (!(global_request= ot_ctx->get_global_mdl_request(thd)))
return 1;
if (! global_request->ticket)
{
ot_ctx->add_request(global_request);
if (thd->mdl_context.acquire_global_intention_exclusive_lock(
global_request))
return 1;
}
ot_ctx->add_request(mdl_request);
if (thd->mdl_context.acquire_exclusive_lock(mdl_request))
return 1;
}
@ -2371,8 +2382,29 @@ open_table_get_mdl_lock(THD *thd, TABLE_LIST *table_list,
if (flags & MYSQL_LOCK_IGNORE_FLUSH)
mdl_request->set_type(MDL_SHARED_HIGH_PRIO);
if (mdl_request->type == MDL_SHARED_UPGRADABLE)
{
MDL_request *global_request;
if (!(global_request= ot_ctx->get_global_mdl_request(thd)))
return 1;
if (! global_request->ticket)
{
ot_ctx->add_request(global_request);
if (thd->mdl_context.try_acquire_global_intention_exclusive_lock(
global_request))
return 1;
if (! global_request->ticket)
goto failure;
}
}
ot_ctx->add_request(mdl_request);
if (thd->mdl_context.try_acquire_shared_lock(mdl_request))
return 1;
failure:
if (mdl_request->ticket == NULL)
{
if (flags & MYSQL_OPEN_FAIL_ON_MDL_CONFLICT)
@ -2919,8 +2951,6 @@ err_unlock:
release_table_share(share);
err_unlock2:
pthread_mutex_unlock(&LOCK_open);
if (! (flags & MYSQL_OPEN_HAS_MDL_LOCK))
thd->mdl_context.release_lock(mdl_ticket);
DBUG_RETURN(TRUE);
}
@ -3713,10 +3743,33 @@ Open_table_context::Open_table_context(THD *thd)
m_start_of_statement_svp(thd->mdl_context.mdl_savepoint()),
m_has_locks((thd->in_multi_stmt_transaction() ||
thd->mdl_context.lt_or_ha_sentinel()) &&
thd->mdl_context.has_locks())
thd->mdl_context.has_locks()),
m_global_mdl_request(NULL)
{}
/**
Get MDL_request object for global intention exclusive lock which
is acquired during opening tables for statements which take
upgradable shared metadata locks.
*/
MDL_request *Open_table_context::get_global_mdl_request(THD *thd)
{
if (! m_global_mdl_request)
{
char *buff;
if ((buff= (char*)thd->alloc(sizeof(MDL_request))))
{
m_global_mdl_request= new (buff) MDL_request();
m_global_mdl_request->init(MDL_key::GLOBAL, "", "",
MDL_INTENTION_EXCLUSIVE);
}
}
return m_global_mdl_request;
}
/**
Check if we can back-off and set back off action if we can.
Otherwise report and return error.
@ -3777,6 +3830,11 @@ recover_from_failed_open(THD *thd, MDL_request *mdl_request,
TABLE_LIST *table)
{
bool result= FALSE;
/*
Remove reference to released ticket from MDL_request.
*/
if (m_global_mdl_request)
m_global_mdl_request->ticket= NULL;
/* Execute the action. */
switch (m_action)
{
@ -3787,11 +3845,26 @@ recover_from_failed_open(THD *thd, MDL_request *mdl_request,
break;
case OT_DISCOVER:
{
MDL_request mdl_global_request;
MDL_request mdl_xlock_request(mdl_request);
mdl_global_request.init(MDL_key::GLOBAL, "", "",
MDL_INTENTION_EXCLUSIVE);
mdl_xlock_request.set_type(MDL_EXCLUSIVE);
if ((result= thd->mdl_context.acquire_global_intention_exclusive_lock(
&mdl_global_request)))
break;
if ((result=
thd->mdl_context.acquire_exclusive_lock(&mdl_xlock_request)))
{
/*
We rely on close_thread_tables() to release global lock eventually.
*/
break;
}
DBUG_ASSERT(mdl_request->key.mdl_namespace() == MDL_key::TABLE);
pthread_mutex_lock(&LOCK_open);
@ -3805,16 +3878,30 @@ recover_from_failed_open(THD *thd, MDL_request *mdl_request,
thd->warning_info->clear_warning_info(thd->query_id);
thd->clear_error(); // Clear error message
thd->mdl_context.release_lock(mdl_xlock_request.ticket);
thd->mdl_context.release_transactional_locks();
break;
}
case OT_REPAIR:
{
MDL_request mdl_global_request;
MDL_request mdl_xlock_request(mdl_request);
mdl_global_request.init(MDL_key::GLOBAL, "", "",
MDL_INTENTION_EXCLUSIVE);
mdl_xlock_request.set_type(MDL_EXCLUSIVE);
if ((result= thd->mdl_context.acquire_global_intention_exclusive_lock(
&mdl_global_request)))
break;
if ((result=
thd->mdl_context.acquire_exclusive_lock(&mdl_xlock_request)))
{
/*
We rely on close_thread_tables() to release global lock eventually.
*/
break;
}
DBUG_ASSERT(mdl_request->key.mdl_namespace() == MDL_key::TABLE);
pthread_mutex_lock(&LOCK_open);
@ -3824,7 +3911,7 @@ recover_from_failed_open(THD *thd, MDL_request *mdl_request,
pthread_mutex_unlock(&LOCK_open);
result= auto_repair_table(thd, table);
thd->mdl_context.release_lock(mdl_xlock_request.ticket);
thd->mdl_context.release_transactional_locks();
break;
}
default:
@ -3921,6 +4008,13 @@ open_and_process_routine(THD *thd, Query_tables_list *prelocking_ctx,
mdl_type != MDL_key::PROCEDURE)
{
ot_ctx->add_request(&rt->mdl_request);
/*
Since we acquire only shared lock on routines we don't
need to care about global intention exclusive locks.
*/
DBUG_ASSERT(rt->mdl_request.type == MDL_SHARED);
if (thd->mdl_context.try_acquire_shared_lock(&rt->mdl_request))
DBUG_RETURN(TRUE);
@ -8784,7 +8878,7 @@ has_write_table_with_auto_increment(TABLE_LIST *tables)
bool
open_system_tables_for_read(THD *thd, TABLE_LIST *table_list,
Open_tables_state *backup)
Open_tables_backup *backup)
{
Query_tables_list query_tables_list_backup;
LEX *lex= thd->lex;
@ -8830,13 +8924,13 @@ error:
SYNOPSIS
close_system_tables()
thd Thread context
backup Pointer to Open_tables_state instance which holds
backup Pointer to Open_tables_backup instance which holds
information about tables which were open before we
decided to access system tables.
*/
void
close_system_tables(THD *thd, Open_tables_state *backup)
close_system_tables(THD *thd, Open_tables_backup *backup)
{
close_thread_tables(thd);
thd->restore_backup_open_tables_state(backup);
@ -8887,7 +8981,7 @@ open_system_table_for_update(THD *thd, TABLE_LIST *one_table)
*/
TABLE *
open_performance_schema_table(THD *thd, TABLE_LIST *one_table,
Open_tables_state *backup)
Open_tables_backup *backup)
{
uint flags= ( MYSQL_LOCK_IGNORE_GLOBAL_READ_LOCK |
MYSQL_LOCK_IGNORE_GLOBAL_READ_ONLY |
@ -8936,51 +9030,9 @@ open_performance_schema_table(THD *thd, TABLE_LIST *one_table,
@param thd The current thread
@param backup [in] the context to restore.
*/
void close_performance_schema_table(THD *thd, Open_tables_state *backup)
void close_performance_schema_table(THD *thd, Open_tables_backup *backup)
{
bool found_old_table;
/*
If open_performance_schema_table() fails,
this function should not be called.
*/
DBUG_ASSERT(thd->lock != NULL);
/*
Note:
We do not create explicitly a separate transaction for the
performance table I/O, but borrow the current transaction.
lock + unlock will autocommit the change done in the
performance schema table: this is the expected result.
The current transaction should not be affected by this code.
TODO: Note that if a transactional engine is used for log tables,
this code will need to be revised, as a separate transaction
might be needed.
*/
mysql_unlock_tables(thd, thd->lock);
thd->lock= 0;
pthread_mutex_lock(&LOCK_open);
found_old_table= false;
/*
Note that we need to hold LOCK_open while changing the
open_tables list. Another thread may work on it.
(See: notify_thread_having_shared_lock())
*/
while (thd->open_tables)
found_old_table|= close_thread_table(thd, &thd->open_tables);
if (found_old_table)
broadcast_refresh();
pthread_mutex_unlock(&LOCK_open);
/* We can't have an open HANDLER in the backup context. */
DBUG_ASSERT(thd->mdl_context.lt_or_ha_sentinel() == NULL);
thd->mdl_context.release_transactional_locks();
thd->restore_backup_open_tables_state(backup);
close_system_tables(thd, backup);
}
/**