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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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20
sql/sql_show.cc
View File

@ -2871,7 +2871,7 @@ make_table_name_list(THD *thd, List<LEX_STRING> *table_names, LEX *lex,
due to metadata locks, so to avoid
them we should not wait in case if
conflicting lock is present.
@param[in] open_tables_state_backup pointer to Open_tables_state object
@param[in] open_tables_state_backup pointer to Open_tables_backup object
which is used to save|restore original
status of variables related to
open tables state
@ -2885,7 +2885,7 @@ static int
fill_schema_show_cols_or_idxs(THD *thd, TABLE_LIST *tables,
ST_SCHEMA_TABLE *schema_table,
bool can_deadlock,
Open_tables_state *open_tables_state_backup)
Open_tables_backup *open_tables_state_backup)
{
LEX *lex= thd->lex;
bool res;
@ -2941,7 +2941,8 @@ fill_schema_show_cols_or_idxs(THD *thd, TABLE_LIST *tables,
table, res, db_name,
table_name));
thd->temporary_tables= 0;
close_tables_for_reopen(thd, &show_table_list, NULL);
close_tables_for_reopen(thd, &show_table_list,
open_tables_state_backup->mdl_system_tables_svp);
DBUG_RETURN(error);
}
@ -3236,8 +3237,12 @@ end_share:
end_unlock:
pthread_mutex_unlock(&LOCK_open);
/*
Don't release the MDL lock, it can be part of a transaction.
If it is not, it will be released by the call to
MDL_context::rollback_to_savepoint() in the caller.
*/
thd->mdl_context.release_lock(table_list.mdl_request.ticket);
thd->clear_error();
return res;
}
@ -3281,7 +3286,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
COND *partial_cond= 0;
uint derived_tables= lex->derived_tables;
int error= 1;
Open_tables_state open_tables_state_backup;
Open_tables_backup open_tables_state_backup;
bool save_view_prepare_mode= lex->view_prepare_mode;
Query_tables_list query_tables_list_backup;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
@ -3500,7 +3505,8 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
res= schema_table->process_table(thd, show_table_list, table,
res, &orig_db_name,
&tmp_lex_string);
close_tables_for_reopen(thd, &show_table_list, NULL);
close_tables_for_reopen(thd, &show_table_list,
open_tables_state_backup.mdl_system_tables_svp);
}
DBUG_ASSERT(!lex->query_tables_own_last);
if (res)
@ -4302,7 +4308,7 @@ int fill_schema_proc(THD *thd, TABLE_LIST *tables, COND *cond)
TABLE *table= tables->table;
bool full_access;
char definer[USER_HOST_BUFF_SIZE];
Open_tables_state open_tables_state_backup;
Open_tables_backup open_tables_state_backup;
DBUG_ENTER("fill_schema_proc");
strxmov(definer, thd->security_ctx->priv_user, "@",