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Browse Source 
----------------------------------------------------------
revno: 2617.69.2
committer: Konstantin Osipov <kostja@sun.com>
branch nick: 5.4-azalea-bugfixing
timestamp: Mon 2009-08-03 19:26:04 +0400
message:
  A fix and a test case for Bug#45035 "Altering table under LOCK TABLES
  results in "Error 1213 Deadlock found...".

  If a user had a table locked with LOCK TABLES
  for READ and for WRITE in the same connection, ALTER TABLE
  could fail.

  Root cause analysis:

  If a connection issues

  LOCK TABLE t1 write, t1 a read, t1 b read;

  the new LOCK TABLES code in 6.0 (part of WL 3726) will create
  the following list of TABLE_LIST objects
  (thd->locked_tables_list->m_locked_tables):

  {"t1" "b" tl_read_no_insert}, {"t1" "a" tl_read_no_insert},
  {"t1" "t1" tl_write }

  Later on, when we try to ALTER table t1, mysql_alter_table()
  closes all TABLE instances and releases its thr_lock locks,
  keeping only an exclusive metadata lock on t1.

  But when ALTER is finished, Locked_table_list::reopen_tables()
  tries to restore the original list of open and locked tables.

  Before this patch, it used to do so one by one:
  Open t1 b, get TL_READ_NO_INSERT lock,
  Open t1 a, get TL_READ_NO_INSERT lock
  Open t1, try to get TL_WRITE lock, deadlock.

  The cause of the deadlock is that thr_lock.c doesn't
  resolve the situation when the read list only consists
  of locks taken by the same thread, followed by this very
  thread trying to take a WRITE lock. Indeed, since
  thr_lock_multi always gets a sorted list of locks,
  WRITE locks always precede READ locks in the list
  to lock.

  Don't try to fix thr_lock.c deficiency, keep this
  code simple.
  Instead, try to take all thr_lock locks at once
  in ::reopen_tables().
This commit is contained in:
Konstantin Osipov
2009-12-08 11:38:45 +03:00
parent b4677ef084
commit 4a8a1c568d
5 changed files with 178 additions and 25 deletions
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19
sql/sql_class.h
View File

@ -1192,7 +1192,7 @@ private:
Therefore, we can't allocate metadata locks on execution memory
root -- as well as tables, the locks need to stay around till
UNLOCK TABLES is called.
The locks are allocated in the memory root encapsulate in this
The locks are allocated in the memory root encapsulated in this
class.
Some SQL commands, like FLUSH TABLE or ALTER TABLE, demand that
@ -1211,10 +1211,21 @@ private:
MEM_ROOT m_locked_tables_root;
TABLE_LIST *m_locked_tables;
TABLE_LIST **m_locked_tables_last;
/** An auxiliary array used only in reopen_tables(). */
TABLE **m_reopen_array;
/**
Count the number of tables in m_locked_tables list. We can't
rely on thd->lock->table_count because it excludes
non-transactional temporary tables. We need to know
an exact number of TABLE objects.
*/
size_t m_locked_tables_count;
public:
Locked_tables_list()
:m_locked_tables(NULL),
m_locked_tables_last(&m_locked_tables)
m_locked_tables_last(&m_locked_tables),
m_reopen_array(NULL),
m_locked_tables_count(0)
{
init_sql_alloc(&m_locked_tables_root, MEM_ROOT_BLOCK_SIZE, 0);
}
@ -1228,7 +1239,9 @@ public:
MEM_ROOT *locked_tables_root() { return &m_locked_tables_root; }
void unlink_from_list(THD *thd, TABLE_LIST *table_list,
bool remove_from_locked_tables);
void unlink_all_closed_tables();
void unlink_all_closed_tables(THD *thd,
MYSQL_LOCK *lock,
size_t reopen_count);
bool reopen_tables(THD *thd);
};