backport dmitry.shulga@oracle.com-20120209125742-w7hdxv0103ymb8ko from mysql-trunk:
Patch for bug#11764747 (formerly known as 57612): SET GLOBAL READ_ONLY=1 cannot
progress when a table is locked with LOCK TABLES.
The reason for the bug was that mysql server makes a flush of all open tables
during handling of statement 'SET GLOBAL READ_ONLY=1'. Therefore if some of
these tables were locked by "LOCK TABLE ... READ" from a different connection,
then execution of statement 'SET GLOBAL READ_ONLY=1' would be waiting for
the lock for such table even if the table was locked in a compatible read mode.
Flushing of all open tables before setting of read_only system variable
is inherited from 5.1 implementation since this was the only possible approach
to ensure that there isn't any pending write operations on open tables.
Start from version 5.5 and above such behaviour is guaranteed by the fact
that we acquire global_read_lock before setting read_only flag. Since
acquiring of global_read_lock is successful only when there isn't any
active write operation then we can remove flushing of open tables from
processing of SET GLOBAL READ_ONLY=1.
This modification changes the server behavior so that read locks held
by other connections (LOCK TABLE ... READ) no longer will block attempts
to enable read_only.
Handle the 'set read_only=1' in lighter way, than the FLUSH TABLES READ LOCK;
For the transactional engines we don't wait for operations on that tables to finish.
per-file comments:
mysql-test/r/read_only_innodb.result
MDEV-136 Non-blocking "set read_only".
test result updated.
mysql-test/t/read_only_innodb.test
MDEV-136 Non-blocking "set read_only".
test case added.
sql/mysql_priv.h
MDEV-136 Non-blocking "set read_only".
The close_cached_tables_set_readonly() declared.
sql/set_var.cc
MDEV-136 Non-blocking "set read_only".
Call close_cached_tables_set_readonly() for the read_only::set_var.
sql/sql_base.cc
MDEV-136 Non-blocking "set read_only".
Parameters added to the close_cached_tables implementation,
close_cached_tables_set_readonly declared.
Prevent blocking on the transactional tables if the
set_readonly_mode is on.
The problem was that in read only mode (read_only enabled),
the server would mistakenly deny data modification attempts
for temporary tables which belong to a transactional storage
engine (eg. InnoDB).
The solution is to allow transactional temporary tables to be
modified under read only mode. As a whole, the read only mode
does not apply to any kind of temporary table.
mysql-test/r/read_only_innodb.result:
Add test case result for Bug#33669
mysql-test/t/read_only_innodb.test:
Add test case for Bug#33669
sql/lock.cc:
Rename mysql_lock_tables_check to lock_tables_check and make
it static. Move locking related checks from get_lock_data to
lock_tables_check. Allow write locks to temporary tables even
under read-only.
------------------------------------------------------------
revno: 2617.68.10
committer: Dmitry Lenev <dlenev@mysql.com>
branch nick: mysql-next-bg46673
timestamp: Tue 2009-09-01 19:57:05 +0400
message:
Fix for bug #46673 "Deadlock between FLUSH TABLES WITH READ LOCK and DML".
Deadlocks occured when one concurrently executed transactions with
several statements modifying data and FLUSH TABLES WITH READ LOCK
statement or SET READ_ONLY=1 statement.
These deadlocks were introduced by the patch for WL 4284: "Transactional
DDL locking"/Bug 989: "If DROP TABLE while there's an active transaction,
wrong binlog order" which has changed FLUSH TABLES WITH READ LOCK/SET
READ_ONLY=1 to wait for pending transactions.
What happened was that FLUSH TABLES WITH READ LOCK blocked all further
statements changing tables by setting global_read_lock global variable
and has started waiting for all pending transactions to complete.
Then one of those transactions tried to executed DML, detected that
global_read_lock non-zero and tried to wait until global read lock will
be released (i.e. global_read_lock becomes 0), indeed, this led to a
deadlock.
Proper solution for this problem should probably involve full integration
of global read lock with metadata locking subsystem (which will allow to
implement waiting for pending transactions without blocking DML in them).
But since it requires significant changes another, short-term solution
for the problem is implemented in this patch.
Basically, this patch restores behavior of FLUSH TABLES WITH READ LOCK/
SET READ_ONLY=1 before the patch for WL 4284/bug 989. By ensuring that
extra references to TABLE_SHARE are not stored for active metadata locks
it changes these statements not to wait for pending transactions.
As result deadlock is eliminated.
Note that this does not change the fact that active FLUSH TABLES WITH
READ LOCK lock or SET READ_ONLY=1 prevent modifications to tables as
they also block transaction commits.
mysql-test/r/flush_block_commit.result:
Adjusted test case after change in FLUSH TABLES WITH READ LOCK behavior
- it is no longer blocked by a pending transaction.
mysql-test/r/mdl_sync.result:
Added test for bug #46673 "Deadlock between FLUSH TABLES WITH READ LOCK
and DML".
mysql-test/r/read_only_innodb.result:
Adjusted test case after change in SET READ_ONLY behavior - it is no
longer blocked by a pending transaction.
mysql-test/t/flush_block_commit.test:
Adjusted test case after change in FLUSH TABLES WITH READ LOCK behavior
- it is no longer blocked by a pending transaction.
mysql-test/t/mdl_sync.test:
Added test for bug #46673 "Deadlock between FLUSH TABLES WITH READ LOCK
and DML".
mysql-test/t/read_only_innodb.test:
Adjusted test case after change in SET READ_ONLY behavior - it is no
longer blocked by a pending transaction.
sql/sql_base.cc:
Disable caching of pointers to TABLE_SHARE objects in MDL subsystem.
This means that transactions holding metadata lock on the table will
no longer have extra reference to the TABLE_SHARE (due to this lock)
and will no longer block concurrent FLUSH TABLES/FLUSH TABLES WITH
READ LOCK. Note that this does not change the fact that FLUSH TABLES
WITH READ LOCK prevents concurrent transactions from modifying data
as it also blocks all commits.
2617.31.12, 2617.31.15, 2617.31.15, 2617.31.16, 2617.43.1
- initial changeset that introduced the fix for
Bug#989 and follow up fixes for all test suite failures
introduced in the initial changeset.
------------------------------------------------------------
revno: 2617.31.1
committer: Davi Arnaut <Davi.Arnaut@Sun.COM>
branch nick: 4284-6.0
timestamp: Fri 2009-03-06 19:17:00 -0300
message:
Bug#989: If DROP TABLE while there's an active transaction, wrong binlog order
WL#4284: Transactional DDL locking
Currently the MySQL server does not keep metadata locks on
schema objects for the duration of a transaction, thus failing
to guarantee the integrity of the schema objects being used
during the transaction and to protect then from concurrent
DDL operations. This also poses a problem for replication as
a DDL operation might be replicated even thought there are
active transactions using the object being modified.
The solution is to defer the release of metadata locks until
a active transaction is either committed or rolled back. This
prevents other statements from modifying the table for the
entire duration of the transaction. This provides commitment
ordering for guaranteeing serializability across multiple
transactions.
- Incompatible change:
If MySQL's metadata locking system encounters a lock conflict,
the usual schema is to use the try and back-off technique to
avoid deadlocks -- this schema consists in releasing all locks
and trying to acquire them all in one go.
But in a transactional context this algorithm can't be utilized
as its not possible to release locks acquired during the course
of the transaction without breaking the transaction commitments.
To avoid deadlocks in this case, the ER_LOCK_DEADLOCK will be
returned if a lock conflict is encountered during a transaction.
Let's consider an example:
A transaction has two statements that modify table t1, then table
t2, and then commits. The first statement of the transaction will
acquire a shared metadata lock on table t1, and it will be kept
utill COMMIT to ensure serializability.
At the moment when the second statement attempts to acquire a
shared metadata lock on t2, a concurrent ALTER or DROP statement
might have locked t2 exclusively. The prescription of the current
locking protocol is that the acquirer of the shared lock backs off
-- gives up all his current locks and retries. This implies that
the entire multi-statement transaction has to be rolled back.
- Incompatible change:
FLUSH commands such as FLUSH PRIVILEGES and FLUSH TABLES WITH READ
LOCK won't cause locked tables to be implicitly unlocked anymore.
mysql-test/extra/binlog_tests/drop_table.test:
Add test case for Bug#989.
mysql-test/extra/binlog_tests/mix_innodb_myisam_binlog.test:
Fix test case to reflect the fact that transactions now hold
metadata locks for the duration of a transaction.
mysql-test/include/mix1.inc:
Fix test case to reflect the fact that transactions now hold
metadata locks for the duration of a transaction.
mysql-test/include/mix2.inc:
Fix test case to reflect the fact that transactions now hold
metadata locks for the duration of a transaction.
mysql-test/r/flush_block_commit.result:
Update test case result (WL#4284).
mysql-test/r/flush_block_commit_notembedded.result:
Update test case result (WL#4284).
mysql-test/r/innodb.result:
Update test case result (WL#4284).
mysql-test/r/innodb_mysql.result:
Update test case result (WL#4284).
mysql-test/r/lock.result:
Add test case result for an effect of WL#4284/Bug#989
(all locks should be released when a connection terminates).
mysql-test/r/mix2_myisam.result:
Update test case result (effects of WL#4284/Bug#989).
mysql-test/r/not_embedded_server.result:
Update test case result (effects of WL#4284/Bug#989).
Add a test case for interaction of WL#4284 and FLUSH PRIVILEGES.
mysql-test/r/partition_innodb_semi_consistent.result:
Update test case result (effects of WL#4284/Bug#989).
mysql-test/r/partition_sync.result:
Temporarily disable the test case for Bug#43867,
which will be fixed by a subsequent backport.
mysql-test/r/ps.result:
Add a test case for effect of PREPARE on transactional
locks: we take a savepoint at beginning of PREAPRE
and release it at the end. Thus PREPARE does not
accumulate metadata locks (Bug#989/WL#4284).
mysql-test/r/read_only_innodb.result:
Update test case result (effects of WL#4284/Bug#989).
mysql-test/suite/binlog/r/binlog_row_drop_tbl.result:
Add a test case result (WL#4284/Bug#989).
mysql-test/suite/binlog/r/binlog_row_mix_innodb_myisam.result:
Update test case result (effects of WL#4284/Bug#989).
mysql-test/suite/binlog/r/binlog_stm_drop_tbl.result:
Add a test case result (WL#4284/Bug#989).
mysql-test/suite/binlog/r/binlog_stm_mix_innodb_myisam.result:
Update test case result (effects of WL#4284/Bug#989).
mysql-test/suite/binlog/r/binlog_unsafe.result:
A side effect of Bug#989 -- slightly different table map ids.
mysql-test/suite/binlog/t/binlog_row_drop_tbl.test:
Add a test case for WL#4284/Bug#989.
mysql-test/suite/binlog/t/binlog_stm_drop_tbl.test:
Add a test case for WL#4284/Bug#989.
mysql-test/suite/binlog/t/binlog_stm_row.test:
Update to the new state name. This
is actually a follow up to another patch for WL#4284,
that changes Locked thread state to Table lock.
mysql-test/suite/ndb/r/ndb_index_ordered.result:
Remove result for disabled part of the test case.
mysql-test/suite/ndb/t/disabled.def:
Temporarily disable a test case (Bug#45621).
mysql-test/suite/ndb/t/ndb_index_ordered.test:
Disable a part of a test case (needs update to
reflect semantics of Bug#989).
mysql-test/suite/rpl/t/disabled.def:
Disable tests made meaningless by transactional metadata
locking.
mysql-test/suite/sys_vars/r/autocommit_func.result:
Add a commit (Bug#989).
mysql-test/suite/sys_vars/t/autocommit_func.test:
Add a commit (Bug#989).
mysql-test/t/flush_block_commit.test:
Fix test case to reflect the fact that transactions now hold
metadata locks for the duration of a transaction.
mysql-test/t/flush_block_commit_notembedded.test:
Fix test case to reflect the fact that transactions now hold
metadata locks for the duration of a transaction.
Add a test case for transaction-scope locks and the global
read lock (Bug#989/WL#4284).
mysql-test/t/innodb.test:
Fix test case to reflect the fact that transactions now hold
metadata locks for the duration of a transaction
(effects of Bug#989/WL#4284).
mysql-test/t/lock.test:
Add a test case for Bug#989/WL#4284.
mysql-test/t/not_embedded_server.test:
Add a test case for Bug#989/WL#4284.
mysql-test/t/partition_innodb_semi_consistent.test:
Replace TRUNCATE with DELETE, to not issue
an implicit commit of a transaction, and not depend
on metadata locks.
mysql-test/t/partition_sync.test:
Temporarily disable the test case for Bug#43867,
which needs a fix to be backported from 6.0.
mysql-test/t/ps.test:
Add a test case for semantics of PREPARE and transaction-scope
locks: metadata locks on tables used in PREPARE are enclosed into a
temporary savepoint, taken at the beginning of PREPARE,
and released at the end. Thus PREPARE does not effect
what locks a transaction owns.
mysql-test/t/read_only_innodb.test:
Fix test case to reflect the fact that transactions now hold
metadata locks for the duration of a transaction
(Bug#989/WL#4284).
Wait for the read_only statement to actually flush tables before
sending other concurrent statements that depend on its state.
mysql-test/t/xa.test:
Fix test case to reflect the fact that transactions now hold
metadata locks for the duration of a transaction
(Bug#989/WL#4284).
sql/ha_ndbcluster_binlog.cc:
Backport bits of changes of ha_ndbcluster_binlog.cc
from 6.0, to fix the failing binlog test suite with
WL#4284. WL#4284 implementation does not work
with 5.1 implementation of ndbcluster binlog index.
sql/log_event.cc:
Release metadata locks after issuing a commit.
sql/mdl.cc:
Style changes (WL#4284).
sql/mysql_priv.h:
Rename parameter to match the name used in the definition (WL#4284).
sql/rpl_injector.cc:
Release metadata locks on commit (WL#4284).
sql/rpl_rli.cc:
Remove assert made meaningless, metadata locks are released
at the end of the transaction.
sql/set_var.cc:
Close tables and release locks if autocommit mode is set.
sql/slave.cc:
Release metadata locks after a rollback.
sql/sql_acl.cc:
Don't implicitly unlock locked tables. Issue a implicit commit
at the end and unlock tables.
sql/sql_base.cc:
Defer the release of metadata locks when closing tables
if not required to.
Issue a deadlock error if the locking protocol requires
that a transaction re-acquire its locks.
Release metadata locks when closing tables for reopen.
sql/sql_class.cc:
Release metadata locks if the thread is killed.
sql/sql_parse.cc:
Release metadata locks after implicitly committing a active
transaction, or after explicit commits or rollbacks.
sql/sql_plugin.cc:
Allocate MDL request on the stack as the use of the table
is contained within the function. It will be removed from
the context once close_thread_tables is called at the end
of the function.
sql/sql_prepare.cc:
The problem is that the prepare phase of the CREATE TABLE
statement takes a exclusive metadata lock lock and this can
cause a self-deadlock the thread already holds a shared lock
on the table being that should be created.
The solution is to make the prepare phase take a shared
metadata lock when preparing a CREATE TABLE statement. The
execution of the statement will still acquire a exclusive
lock, but won't cause any problem as it issues a implicit
commit.
After some discussions with stakeholders it has been decided that
metadata locks acquired during a PREPARE statement must be released
once the statement is prepared even if it is prepared within a multi
statement transaction.
sql/sql_servers.cc:
Don't implicitly unlock locked tables. Issue a implicit commit
at the end and unlock tables.
sql/sql_table.cc:
Close table and release metadata locks after a admin operation.
sql/table.h:
The problem is that the prepare phase of the CREATE TABLE
statement takes a exclusive metadata lock lock and this can
cause a self-deadlock the thread already holds a shared lock
on the table being that should be created.
The solution is to make the prepare phase take a shared
metadata lock when preparing a CREATE TABLE statement. The
execution of the statement will still acquire a exclusive
lock, but won't cause any problem as it issues a implicit
commit.
sql/transaction.cc:
Release metadata locks after the implicitly committed due
to a new transaction being started. Also, release metadata
locks acquired after a savepoint if the transaction is rolled
back to the save point.
The problem is that in some cases transaction-long metadata locks
could be released before the transaction was committed. This could
happen when a active transaction was ended by a "START TRANSACTION"
or "BEGIN" statement, in which case the metadata locks would be
released before the actual commit of the active transaction.
The solution is to defer the release of metadata locks to after the
transaction has been implicitly committed. No test case is provided
as the effort to provide one is too disproportional to the size of
the fix.
Problem: SELECTs prohibited for a transactional SE in autocommit mode
if read_only is set.
Fix: allow them.
mysql-test/r/read_only_innodb.result:
Fix for bug #35732: read-only blocks SELECT statements in InnoDB
- test result.
mysql-test/t/read_only_innodb.test:
Fix for bug #35732: read-only blocks SELECT statements in InnoDB
- test case.
sql/handler.cc:
Fix for bug #35732: read-only blocks SELECT statements in InnoDB
- in autocommit mode thd->transaction.all list is empty thus
is_real_trans set to TRUE for any SELECTs, so using it in the
"read_only" check is insufficient.
ha_check_and_coalesce_trx_read_only() changed to return number
of engines with read-write changes. This value is used in the
"read-only" check and checks for GLOBAL READ LOCK.
sql/lock.cc:
Fix for bug #35732: read-only blocks SELECT statements in InnoDB
- added assert(protect_against_global_read_lock) before decreasing,
in order to catch (uint) 0 - 1 situation due to wrong
wait_if_global_read_lock()/start_waiting_global_read_lock() call
sequence.
Bug#11733 (COMMITs should not happen if read-only is set)
Bug#22009 (Can write to a read-only server under some circumstances)
See the work log for details
The change consist of
a) acquiring the global read lock in SET GLOBAL READONLY
b) honoring opt_readonly in ha_commit_trans(),
c) honoring opt_readonly in mysql_lock_tables().
a) takes care of the server stability,
b) makes the transactional tables safe (Bug 11733)
c) makes the non transactional tables safe (Bug 22009)
mysql-test/r/read_only.result:
WL#3602 (SET GLOBAL READONLY)
mysql-test/t/read_only.test:
WL#3602 (SET GLOBAL READONLY)
sql/handler.cc:
WL#3602 (SET GLOBAL READONLY)
sql/lock.cc:
WL#3602 (SET GLOBAL READONLY)
sql/set_var.cc:
WL#3602 (SET GLOBAL READONLY)
sql/set_var.h:
WL#3602 (SET GLOBAL READONLY)
mysql-test/r/read_only_innodb.result:
WL#3602 (SET GLOBAL READONLY)
mysql-test/t/read_only_innodb.test:
WL#3602 (SET GLOBAL READONLY)
