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Bug#43230: SELECT ... FOR UPDATE can hang with FLUSH TABLES WITH READ LOCK indefinitely

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The problem is that a SELECT .. FOR UPDATE statement might open
a table and later wait for a impeding global read lock without
noticing whether it is holding a table that is being waited upon
the the flush phase of the process that took the global read
lock.

The same problem also affected the following statements:

LOCK TABLES .. WRITE
UPDATE .. SET (update and multi-table update)
TRUNCATE TABLE ..
LOAD DATA ..

The solution is to make the above statements wait for a impending
global read lock before opening the tables. If there is no
impending global read lock, the statement raises a temporary
protection against global read locks and progresses smoothly
towards completion.

Important notice: the patch does not try to address all possible
cases, only those which are common and can be fixed unintrusively
enough for 5.0.

mysql-test/r/lock_multi.result:
  Add test case result for Bug#43230
mysql-test/t/lock_multi.test:
  Add test case for Bug#43230
sql/sql_lex.cc:
  Initialize flag.
sql/sql_lex.h:
  Add a flag to the lexer.
sql/sql_parse.cc:
  Wait for the global read lock is a write lock is going to be
  taken. The wait is done before opening tables.
sql/sql_yacc.yy:
  Protect against the GRL if its a SELECT .. FOR UPDATE or LOCK TABLES
  .. WRITE statement.
This commit is contained in:
Davi Arnaut
2009-04-03 16:11:54 -03:00
parent 02f8ec4d76
commit 72e978828e
6 changed files with 231 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
sql/sql_parse.cc
View File

@ -2800,6 +2800,10 @@ mysql_execute_command(THD *thd)
if (res)
goto error;
if (!thd->locked_tables && lex->protect_against_global_read_lock &&
!(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
goto error;
if (!(res= open_and_lock_tables(thd, all_tables)))
{
if (lex->describe)
@ -3660,6 +3664,9 @@ end_with_restore_list:
DBUG_ASSERT(first_table == all_tables && first_table != 0);
if (update_precheck(thd, all_tables))
break;
if (!thd->locked_tables &&
!(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
goto error;
DBUG_ASSERT(select_lex->offset_limit == 0);
unit->set_limit(select_lex);
res= (up_result= mysql_update(thd, all_tables,
@ -3686,6 +3693,15 @@ end_with_restore_list:
else
res= 0;
/*
Protection might have already been risen if its a fall through
from the SQLCOM_UPDATE case above.
*/
if (!thd->locked_tables &&
lex->sql_command == SQLCOM_UPDATE_MULTI &&
!(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
goto error;
res= mysql_multi_update_prepare(thd);
#ifdef HAVE_REPLICATION
@ -3853,7 +3869,8 @@ end_with_restore_list:
ER(ER_LOCK_OR_ACTIVE_TRANSACTION), MYF(0));
goto error;
}
if (!(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
goto error;
res= mysql_truncate(thd, first_table, 0);
break;
case SQLCOM_DELETE:
@ -4027,6 +4044,10 @@ end_with_restore_list:
if (check_one_table_access(thd, privilege, all_tables))
goto error;
if (!thd->locked_tables &&
!(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
goto error;
res= mysql_load(thd, lex->exchange, first_table, lex->field_list,
lex->update_list, lex->value_list, lex->duplicates,
lex->ignore, (bool) lex->local_file);
@ -4082,6 +4103,9 @@ end_with_restore_list:
goto error;
if (check_table_access(thd, LOCK_TABLES_ACL | SELECT_ACL, all_tables, 0))
goto error;
if (lex->protect_against_global_read_lock &&
!(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
goto error;
thd->in_lock_tables=1;
thd->options|= OPTION_TABLE_LOCK;