which implemented new type-of-operation-aware metadata
locks and added a wait-for graph based deadlock detector
to the MDL subsystem (this patch fixed bug #46272 "MySQL
5.4.4, new MDL: unnecessary deadlock" and bug #37346
"innodb does not detect deadlock between update and alter
table").
These hangs were caused by missing include of
wait_condition.inc. This fix simply adds them.
mysql-test/t/mdl_sync.test:
Added missing include of wait_condition.inc.
caused by patch which implemented new type-of-operation-aware
metadata locks and added a wait-for graph based deadlock
detector to the MDL subsystem (this patch fixed bug #46272
"MySQL 5.4.4, new MDL: unnecessary deadlock" and bug #37346
"innodb does not detect deadlock between update and alter
table").
Crashes were caused by a race in MDL_context::try_acquire_lock().
This method added MDL_ticket to the list of granted tickets and
released lock protecting list before setting MDL_ticket::m_lock.
Thus some other thread was able to see ticket without properly
set m_lock member for some short period of time. If this thread
called method involving this member during this period crash
happened.
This fix ensures that MDL_ticket::m_lock is set in all cases
when ticket is added to granted/pending lists in MDL_lock.
sql/mdl.cc:
We must set MDL_ticket::m_lock member before adding ticket
to the list of granted tickets, since such tickets can be
accessed by other threads which might call methods using
this member.
Added assert which ensures that all MDL_tickets which are
added to the granted/pending lists have properly set
MDL_ticket::m_lock member.
sql/mdl.h:
Adjusted comment describing MDL_ticket::m_lock member to
reflect current reality.
Added accessor method for this member.
Add a wait-for graph based deadlock detector to the
MDL subsystem.
Fixes bug #46272 "MySQL 5.4.4, new MDL: unnecessary deadlock" and
bug #37346 "innodb does not detect deadlock between update and
alter table".
The first bug manifested itself as an unwarranted abort of a
transaction with ER_LOCK_DEADLOCK error by a concurrent ALTER
statement, when this transaction tried to repeat use of a
table, which it has already used in a similar fashion before
ALTER started.
The second bug showed up as a deadlock between table-level
locks and InnoDB row locks, which was "detected" only after
innodb_lock_wait_timeout timeout.
A transaction would start using the table and modify a few
rows.
Then ALTER TABLE would come in, and start copying rows
into a temporary table. Eventually it would stumble on
the modified records and get blocked on a row lock.
The first transaction would try to do more updates, and get
blocked on thr_lock.c lock.
This situation of circular wait would only get resolved
by a timeout.
Both these bugs stemmed from inadequate solutions to the
problem of deadlocks occurring between different
locking subsystems.
In the first case we tried to avoid deadlocks between metadata
locking and table-level locking subsystems, when upgrading shared
metadata lock to exclusive one.
Transactions holding the shared lock on the table and waiting for
some table-level lock used to be aborted too aggressively.
We also allowed ALTER TABLE to start in presence of transactions
that modify the subject table. ALTER TABLE acquires
TL_WRITE_ALLOW_READ lock at start, and that block all writes
against the table (naturally, we don't want any writes to be lost
when switching the old and the new table). TL_WRITE_ALLOW_READ
lock, in turn, would block the started transaction on thr_lock.c
lock, should they do more updates. This, again, lead to the need
to abort such transactions.
The second bug occurred simply because we didn't have any
mechanism to detect deadlocks between the table-level locks
in thr_lock.c and row-level locks in InnoDB, other than
innodb_lock_wait_timeout.
This patch solves both these problems by moving lock conflicts
which are causing these deadlocks into the metadata locking
subsystem, thus making it possible to avoid or detect such
deadlocks inside MDL.
To do this we introduce new type-of-operation-aware metadata
locks, which allow MDL subsystem to know not only the fact that
transaction has used or is going to use some object but also what
kind of operation it has carried out or going to carry out on the
object.
This, along with the addition of a special kind of upgradable
metadata lock, allows ALTER TABLE to wait until all
transactions which has updated the table to go away.
This solves the second issue.
Another special type of upgradable metadata lock is acquired
by LOCK TABLE WRITE. This second lock type allows to solve the
first issue, since abortion of table-level locks in event of
DDL under LOCK TABLES becomes also unnecessary.
Below follows the list of incompatible changes introduced by
this patch:
- From now on, ALTER TABLE and CREATE/DROP TRIGGER SQL (i.e. those
statements that acquire TL_WRITE_ALLOW_READ lock)
wait for all transactions which has *updated* the table to
complete.
- From now on, LOCK TABLES ... WRITE, REPAIR/OPTIMIZE TABLE
(i.e. all statements which acquire TL_WRITE table-level lock) wait
for all transaction which *updated or read* from the table
to complete.
As a consequence, innodb_table_locks=0 option no longer applies
to LOCK TABLES ... WRITE.
- DROP DATABASE, DROP TABLE, RENAME TABLE no longer abort
statements or transactions which use tables being dropped or
renamed, and instead wait for these transactions to complete.
- Since LOCK TABLES WRITE now takes a special metadata lock,
not compatible with with reads or writes against the subject table
and transaction-wide, thr_lock.c deadlock avoidance algorithm
that used to ensure absence of deadlocks between LOCK TABLES
WRITE and other statements is no longer sufficient, even for
MyISAM. The wait-for graph based deadlock detector of MDL
subsystem may sometimes be necessary and is involved. This may
lead to ER_LOCK_DEADLOCK error produced for multi-statement
transactions even if these only use MyISAM:
session 1: session 2:
begin;
update t1 ... lock table t2 write, t1 write;
-- gets a lock on t2, blocks on t1
update t2 ...
(ER_LOCK_DEADLOCK)
- Finally, support of LOW_PRIORITY option for LOCK TABLES ... WRITE
was abandoned.
LOCK TABLE ... LOW_PRIORITY WRITE from now on has the same
priority as the usual LOCK TABLE ... WRITE.
SELECT HIGH PRIORITY no longer trumps LOCK TABLE ... WRITE in
the wait queue.
- We do not take upgradable metadata locks on implicitly
locked tables. So if one has, say, a view v1 that uses
table t1, and issues:
LOCK TABLE v1 WRITE;
FLUSH TABLE t1; -- (or just 'FLUSH TABLES'),
an error is produced.
In order to be able to perform DDL on a table under LOCK TABLES,
the table must be locked explicitly in the LOCK TABLES list.
mysql-test/include/handler.inc:
Adjusted test case to trigger an execution path on which bug 41110
"crash with handler command when used concurrently with alter
table" and bug 41112 "crash in mysql_ha_close_table/get_lock_data
with alter table" were originally discovered. Left old test case
which no longer triggers this execution path for the sake of
coverage.
Added test coverage for HANDLER SQL statements and type-aware
metadata locks.
Added a test for the global shared lock and HANDLER SQL.
Updated tests to take into account that the old simple deadlock
detection heuristics was replaced with a graph-based deadlock
detector.
mysql-test/r/debug_sync.result:
Updated results (see debug_sync.test).
mysql-test/r/handler_innodb.result:
Updated results (see handler.inc test).
mysql-test/r/handler_myisam.result:
Updated results (see handler.inc test).
mysql-test/r/innodb-lock.result:
Updated results (see innodb-lock.test).
mysql-test/r/innodb_mysql_lock.result:
Updated results (see innodb_mysql_lock.test).
mysql-test/r/lock.result:
Updated results (see lock.test).
mysql-test/r/lock_multi.result:
Updated results (see lock_multi.test).
mysql-test/r/lock_sync.result:
Updated results (see lock_sync.test).
mysql-test/r/mdl_sync.result:
Updated results (see mdl_sync.test).
mysql-test/r/sp-threads.result:
SHOW PROCESSLIST output has changed due to the fact that waiting
for LOCK TABLES WRITE now happens within metadata locking
subsystem.
mysql-test/r/truncate_coverage.result:
Updated results (see truncate_coverage.test).
mysql-test/suite/funcs_1/datadict/processlist_val.inc:
SELECT FROM I_S.PROCESSLIST output has changed due to fact that
waiting for LOCK TABLES WRITE now happens within metadata locking
subsystem.
mysql-test/suite/funcs_1/r/processlist_val_no_prot.result:
SELECT FROM I_S.PROCESSLIST output has changed due to fact that
waiting for LOCK TABLES WRITE now happens within metadata locking
subsystem.
mysql-test/suite/rpl/t/rpl_sp.test:
Updated to a new SHOW PROCESSLIST state name.
mysql-test/t/debug_sync.test:
Use LOCK TABLES READ instead of LOCK TABLES WRITE as the latter
no longer allows to trigger execution path involving waiting on
thr_lock.c lock and therefore reaching debug sync-point covered
by this test.
mysql-test/t/innodb-lock.test:
Adjusted test case to the fact that innodb_table_locks=0 option is
no longer supported, since LOCK TABLES WRITE handles all its
conflicts within MDL subsystem.
mysql-test/t/innodb_mysql_lock.test:
Added test for bug #37346 "innodb does not detect deadlock between
update and alter table".
mysql-test/t/lock.test:
Added test coverage which checks the fact that we no longer support
DDL under LOCK TABLES on tables which were locked implicitly.
Adjusted existing test cases accordingly.
mysql-test/t/lock_multi.test:
Added test for bug #46272 "MySQL 5.4.4, new MDL: unnecessary
deadlock". Adjusted other test cases to take into account the
fact that waiting for LOCK TABLES ... WRITE now happens within MDL
subsystem.
mysql-test/t/lock_sync.test:
Since LOCK TABLES ... WRITE now takes SNRW metadata lock for
tables locked explicitly we have to implicitly lock InnoDB tables
(through view) to trigger the table-level lock conflict between
TL_WRITE and TL_WRITE_ALLOW_WRITE.
mysql-test/t/mdl_sync.test:
Added basic test coverage for type-of-operation-aware metadata
locks. Also covered with tests some use cases involving HANDLER
statements in which a deadlock could arise.
Adjusted existing tests to take type-of-operation-aware MDL into
account.
mysql-test/t/multi_update.test:
Update to a new SHOW PROCESSLIST state name.
mysql-test/t/truncate_coverage.test:
Adjusted test case after making LOCK TABLES WRITE to wait until
transactions that use the table to be locked are completed.
Updated to the changed name of DEBUG_SYNC point.
sql/handler.cc:
Global read lock functionality has been
moved into a class.
sql/lock.cc:
Global read lock functionality has been
moved into a class.
Updated code to use the new MDL API.
sql/mdl.cc:
Introduced new type-of-operation aware metadata locks.
To do this:
- Changed MDL_lock to use one list for waiting requests and one
list for granted requests. For each list, added a bitmap
that holds information what lock types a list contains.
Added a helper class MDL_lock::List to manipulate with granted
and waited lists while keeping the bitmaps in sync
with list contents.
- Changed lock-compatibility functions to use bitmaps that
define compatibility.
- Introduced a graph based deadlock detector inspired by
waiting_threads.c from Maria implementation.
- Now that we have a deadlock detector, and no longer have
a global lock to protect individual lock objects, but rather
use an rw lock per object, removed redundant code for upgrade,
and the global read lock. Changed the MDL API to
no longer require the caller to acquire the global
intention exclusive lock by means of a separate method.
Removed a few more methods that became redundant.
- Removed deadlock detection heuristic, it has been made
obsolete by the deadlock detector.
- With operation-type-aware metadata locks, MDL subsystem has
become aware of potential conflicts between DDL and open
transactions. This made it possible to remove calls to
mysql_abort_transactions_with_shared_lock() from acquisition
paths for exclusive lock and lock upgrade. Now we can simply
wait for these transactions to complete without fear of
deadlock. Function mysql_lock_abort() has also become
unnecessary for all conflicting cases except when a DDL
conflicts with a connection that has an open HANDLER.
sql/mdl.h:
Introduced new type-of-operation aware metadata locks.
Introduced a graph based deadlock detector and supporting
methods.
Added comments.
God rid of redundant API calls.
Renamed m_lt_or_ha_sentinel to m_trans_sentinel,
since now it guards the global read lock as well as
LOCK TABLES and HANDLER locks.
sql/mysql_priv.h:
Moved the global read lock functionality into a
class.
Added MYSQL_OPEN_FORCE_SHARED_MDL flag which forces
open_tables() to take MDL_SHARED on tables instead of
metadata locks specified in the parser. We use this to
allow PREPARE run concurrently in presence of
LOCK TABLES ... WRITE.
Added signature for find_table_for_mdl_ugprade().
sql/set_var.cc:
Global read lock functionality has been
moved into a class.
sql/sp_head.cc:
When creating TABLE_LIST elements for prelocking or
system tables set the type of request for metadata
lock according to the operation that will be performed
on the table.
sql/sql_base.cc:
- Updated code to use the new MDL API.
- In order to avoid locks starvation we take upgradable
locks all at once. As result implicitly locked tables no
longer get an upgradable lock. Consequently DDL and FLUSH
TABLES for such tables is prohibited.
find_write_locked_table() was replaced by
find_table_for_mdl_upgrade() function.
open_table() was adjusted to return TABLE instance with
upgradable ticket when necessary.
- We no longer wait for all locks on OT_WAIT back off
action -- only on the lock that caused the wait
conflict. Moreover, now we distinguish cases when we
have to wait due to conflict in MDL and old version
of table in TDC.
- Upate mysql_notify_threads_having_share_locks()
to only abort thr_lock.c waits of threads that
have open HANDLERs, since lock conflicts with only
these threads now can lead to deadlocks not detectable
by the MDL deadlock detector.
- Remove mysql_abort_transactions_with_shared_locks()
which is no longer needed.
sql/sql_class.cc:
Global read lock functionality has been moved into a class.
Re-arranged code in THD::cleanup() to simplify assert.
sql/sql_class.h:
Introduced class to incapsulate global read lock
functionality.
Now sentinel in MDL subsystem guards the global read lock
as well as LOCK TABLES and HANDLER locks. Adjusted code
accordingly.
sql/sql_db.cc:
Global read lock functionality has been moved into a class.
sql/sql_delete.cc:
We no longer acquire upgradable metadata locks on tables
which are locked by LOCK TABLES implicitly. As result
TRUNCATE TABLE is no longer allowed for such tables.
Updated code to use the new MDL API.
sql/sql_handler.cc:
Inform MDL_context about presence of open HANDLERs.
Since HANLDERs break MDL protocol by acquiring table-level
lock while holding only S metadata lock on a table MDL
subsystem should take special care about such contexts (Now
this is the only case when mysql_lock_abort() is used).
sql/sql_parse.cc:
Global read lock functionality has been moved into a class.
Do not take upgradable metadata locks when opening tables
for CREATE TABLE SELECT as it is not necessary and limits
concurrency.
When initializing TABLE_LIST objects before adding them
to the table list set the type of request for metadata lock
according to the operation that will be performed on the
table.
We no longer acquire upgradable metadata locks on tables
which are locked by LOCK TABLES implicitly. As result FLUSH
TABLES is no longer allowed for such tables.
sql/sql_prepare.cc:
Use MYSQL_OPEN_FORCE_SHARED_MDL flag when opening
tables during PREPARE. This allows PREPARE to run
concurrently in presence of LOCK TABLES ... WRITE.
sql/sql_rename.cc:
Global read lock functionality has been moved into a class.
sql/sql_show.cc:
Updated code to use the new MDL API.
sql/sql_table.cc:
Global read lock functionality has been moved into a class.
We no longer acquire upgradable metadata locks on tables
which are locked by LOCK TABLES implicitly. As result DROP
TABLE is no longer allowed for such tables.
Updated code to use the new MDL API.
sql/sql_trigger.cc:
Global read lock functionality has been moved into a class.
We no longer acquire upgradable metadata locks on tables
which are locked by LOCK TABLES implicitly. As result
CREATE/DROP TRIGGER is no longer allowed for such tables.
Updated code to use the new MDL API.
sql/sql_view.cc:
Global read lock functionality has been moved into a class.
Fixed results of wrong merge that led to misuse of GLR API.
CREATE VIEW statement is not a commit statement.
sql/table.cc:
When resetting TABLE_LIST objects for PS or SP re-execution
set the type of request for metadata lock according to the
operation that will be performed on the table. Do the same
in auxiliary function initializing metadata lock requests
in a table list.
sql/table.h:
When initializing TABLE_LIST objects set the type of request
for metadata lock according to the operation that will be
performed on the table.
sql/transaction.cc:
Global read lock functionality has been moved into a class.
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.
mysql-test/include/handler.inc:
Adjusted handler_myisam.test and handler_innodb.test to the fact that
exclusive metadata locks on tables are now acquired according to
alphabetical order of fully qualified table names instead of order
in which tables are mentioned in statement.
mysql-test/r/handler_innodb.result:
Adjusted handler_myisam.test and handler_innodb.test to the fact that
exclusive metadata locks on tables are now acquired according to
alphabetical order of fully qualified table names instead of order
in which tables are mentioned in statement.
mysql-test/r/handler_myisam.result:
Adjusted handler_myisam.test and handler_innodb.test to the fact that
exclusive metadata locks on tables are now acquired according to
alphabetical order of fully qualified table names instead of order
in which tables are mentioned in statement.
mysql-test/r/mdl_sync.result:
Adjusted mdl_sync.test to the fact that exclusive metadata locks on
tables are now acquired according to alphabetical order of fully
qualified table names instead of order in which tables are mentioned
in statement.
mysql-test/t/mdl_sync.test:
Adjusted mdl_sync.test to the fact that exclusive metadata locks on
tables are now acquired according to alphabetical order of fully
qualified table names instead of order in which tables are mentioned
in statement.
sql/events.cc:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. As result code
opening/closing system tables was changed to use Open_tables_backup
instead of Open_table_state class as well.
sql/ha_ndbcluster.cc:
Since manipulations with open table state no longer install proxy
MDL_context it does not make sense to perform them in order to
satisfy assert in mysql_rm_tables_part2(). Removed them per agreement
with Cluster team. This has not broken test suite since scenario in
which deadlock can occur and assertion fails is not covered by tests.
sql/lock.cc:
MDL subsystem no longer implicitly acquires global intention exclusive
metadata lock when per-object exclusive metadata lock is acquired.
Now this has to be done by explicit calls outside of MDL subsystem.
sql/log.cc:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. As result code
opening/closing system tables was changed to use Open_tables_backup
instead of Open_table_state class as well.
sql/mdl.cc:
Changed metadata locking subsystem to use mutex per lock and condition
variable per context instead of one mutex and one conditional variable
for the whole subsystem.
Changed approach to handling of global metadata locks. Instead of
implicitly acquiring intention exclusive locks when user requests
per-object upgradeable or exclusive locks now we require them to be
acquired explicitly in the same way as ordinary metadata locks.
In fact global lock are now ordinary metadata locks in new GLOBAL
namespace.
To implement these changes:
- Removed LOCK_mdl mutex and COND_mdl condition variable.
- Introduced MDL_lock::m_mutex mutexes which protect individual lock
objects.
- Replaced mdl_locks hash with MDL_map class, which has hash for
MDL_lock objects as a member and separate mutex which protects this
hash. Methods of this class allow to find(), find_or_create() or
remove() MDL_lock objects in concurrency-friendly fashion (i.e.
for most common operation, find_or_create(), we don't acquire
MDL_lock::m_mutex while holding MDL_map::m_mutex. Thanks to MikaelR
for this idea and benchmarks!). Added three auxiliary members to
MDL_lock class (m_is_destroyed, m_ref_usage, m_ref_release) to
support this concurrency-friendly behavior.
- Introduced MDL_context::m_ctx_wakeup_cond condition variable to be
used for waiting until this context's pending request can be
satisfied or its thread has to perform actions to resolve potential
deadlock. Context which want to wait add ticket corresponding to the
request to an appropriate queue of waiters in MDL_lock object so
they can be noticed when other contexts change state of lock and be
awaken by them by signalling on MDL_context::m_ctx_wakeup_cond.
As consequence MDL_ticket objects has to be used for any waiting
in metadata locking subsystem including one which happens in
MDL_context::wait_for_locks() method.
Another consequence is that MDL_context is no longer copyable and
can't be saved/restored when working with system tables.
- Made MDL_lock an abstract class, which delegates specifying exact
compatibility matrix to its descendants. Added MDL_global_lock child
class for global lock (The old is_lock_type_compatible() method
became can_grant_lock() method of this class). Added MDL_object_lock
class to represent per-object lock (The old MDL_lock::can_grant_lock()
became its method). Choice between two classes happens based on MDL
namespace in MDL_lock::create() method.
- Got rid of MDL_lock::type member as its meaning became ambigous for
global locks.
- To simplify waking up of contexts waiting for lock split waiting queue
in MDL_lock class in two queues. One for pending requests for exclusive
(including intention exclusive) locks and another for requests for
shared locks.
- Added virtual wake_up_waiters() method to MDL_lock, MDL_global_lock and
MDL_object_lock classes which allows to wake up waiting contexts after
state of lock changes. Replaced old duplicated code with calls to this
method.
- Adjusted MDL_context::try_acquire_shared_lock()/exclusive_lock()/
global_shared_lock(), MDL_ticket::upgrade_shared_lock_to_exclusive_lock()
and MDL_context::release_ticket() methods to use MDL_map and
MDL_lock::m_mutex instead of single LOCK_mdl mutex and wake up
waiters according to the approach described above. The latter method
also was renamed to MDL_context::release_lock().
- Changed MDL_context::try_acquire_shared_lock()/exclusive_lock() and
release_lock() not to handle global locks. They are now supposed to
be taken explicitly like ordinary metadata locks.
- Added helper MDL_context::try_acquire_global_intention_exclusive_lock()
and acquire_global_intention_exclusive_lock() methods.
- Moved common code from MDL_context::acquire_global_shared_lock() and
acquire_global_intention_exclusive_lock() to new method -
MDL_context::acquire_lock_impl().
- Moved common code from MDL_context::try_acquire_shared_lock(),
try_acquire_global_intention_exclusive_lock()/exclusive_lock()
to MDL_context::try_acquire_lock_impl().
- Since acquiring of several exclusive locks can no longer happen under
single LOCK_mdl mutex the approach to it had to be changed. Now we do
it in one by one fashion. This is done in alphabetical order to avoid
deadlocks. Changed MDL_context::acquire_exclusive_locks() accordingly
(as part of this change moved code responsible for acquiring single
exclusive lock to new MDL_context::acquire_exclusive_lock_impl()
method).
- Since we no longer have single LOCK_mdl mutex which protects all
MDL_context::m_is_waiting_in_mdl members using these members to
determine if we have really awaken context holding conflicting
shared lock became inconvinient. Got rid of this member and changed
notify_shared_lock() helper function and process of acquiring
of/upgrading to exclusive lock not to rely on such information.
Now in MDL_context::acquire_exclusive_lock_impl() and
MDL_ticket::upgrade_shared_lock_to_exclusive_lock() we simply
re-try to wake up threads holding conflicting shared locks after
small time out.
- Adjusted MDL_context::can_wait_lead_to_deadlock() and
MDL_ticket::has_pending_conflicting_lock() to use per-lock
mutexes instead of LOCK_mdl. To do this introduced
MDL_lock::has_pending_exclusive_lock() method.
sql/mdl.h:
Changed metadata locking subsystem to use mutex per lock and condition
variable per context instead of one mutex and one conditional variable
for the whole subsystem. In order to implement this change:
- Added MDL_key::cmp() method to be able to sort MDL_key objects
alphabetically. Changed length fields in MDL_key class to uint16
as 16-bit is enough for length of any key.
- Changed MDL_ticket::get_ctx() to return pointer to non-const
object in order to be able to use MDL_context::awake() method
for such contexts.
- Got rid of unlocked versions of can_wait_lead_to_deadlock()/
has_pending_conflicting_lock() methods in MDL_context and
MDL_ticket. We no longer has single mutex which protects all
locks. Thus one always has to use versions of these methods
which acquire per-lock mutexes.
- MDL_request_list type of list now counts its elements.
- Added MDL_context::m_ctx_wakeup_cond condition variable to be used
for waiting until this context's pending request can be satisfied
or its thread has to perform actions to resolve potential deadlock.
Added awake() method to wake up context from such wait.
Addition of condition variable made MDL_context uncopyable.
As result we no longer can save/restore MDL_context when working
with system tables. Instead we create MDL savepoint before opening
those tables and rollback to it once they are closed.
- MDL_context::release_ticket() became release_lock() method.
- Added auxiliary MDL_context::acquire_exclusive_lock_impl() method
which does all necessary work to acquire exclusive lock on one object
but should not be used directly as it does not enforce any asserts
ensuring that no deadlocks are possible.
- Since we no longer need to know if thread trying to acquire exclusive
lock managed to wake up any threads having conflicting shared locks
(as, anyway, we will try to wake up such threads again shortly)
- MDL_context::m_is_waiting_in_mdl member became unnecessary and
notify_shared_lock() no longer needs to be friend of MDL_context.
Changed approach to handling of global metadata locks. Instead of
implicitly acquiring intention exclusive locks when user requests
per-object upgradeable or exclusive locks now we require them to be
acquired explicitly in the same way as ordinary metadata locks.
- Added new GLOBAL namespace for such locks.
- Added new type of lock to be requested MDL_INTENTION_EXCLISIVE.
- Added MDL_context::try_acquire_global_intention_exclusive_lock()
and acquire_global_intention_exclusive_lock() methods.
- Moved common code from MDL_context::acquire_global_shared_lock()
and acquire_global_intention_exclusive_lock() to new method -
MDL_context::acquire_lock_impl().
- Moved common code from MDL_context::try_acquire_shared_lock(),
try_acquire_global_intention_exclusive_lock()/exclusive_lock()
to MDL_context::try_acquire_lock_impl().
- Added helper MDL_context::is_global_lock_owner() method to be
able easily to find what kind of global lock this context holds.
- MDL_context::m_has_global_shared_lock became unnecessary as
global read lock is now represented by ordinary ticket.
- Removed assert in MDL_context::set_lt_or_ha_sentinel() which became
false for cases when we execute LOCK TABLES under global read lock
mode.
sql/mysql_priv.h:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. As result calls
opening/closing system tables were changed to use Open_tables_backup
instead of Open_table_state class as well.
sql/sp.cc:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. As result code
opening/closing system tables was changed to use Open_tables_backup
instead of Open_table_state class as well.
sql/sp.h:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. As result code
opening/closing system tables was changed to use Open_tables_backup
instead of Open_table_state class as well.
sql/sql_base.cc:
close_thread_tables():
Since we no longer use separate MDL_context for opening system
tables we need to avoid releasing all transaction locks when
closing system table. Releasing metadata lock on system table
is now responsibility of THD::restore_backup_open_tables_state().
open_table_get_mdl_lock(),
Open_table_context::recover_from_failed_open():
MDL subsystem no longer implicitly acquires global intention exclusive
metadata lock when per-object upgradable or exclusive metadata lock is
acquired. So this have to be done explicitly from these calls.
Changed Open_table_context class to store MDL_request object for
global intention exclusive lock acquired when opening tables.
open_table():
Do not release metadata lock if we have failed to open table as
this lock might have been acquired by one of previous statements
in transaction, and therefore should not be released.
open_system_tables_for_read()/close_system_tables()/
open_performance_schema_table():
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. As result code
opening/closing system tables was changed to use Open_tables_backup
instead of Open_table_state class as well.
close_performance_schema_table():
Got rid of duplicated code.
sql/sql_class.cc:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. Also releasing
metadata lock on system table is now responsibility of
THD::restore_backup_open_tables_state().
Adjusted assert in THD::cleanup() to take into account fact that now
we also use MDL sentinel for global read lock.
sql/sql_class.h:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. As result:
- 'mdl_context' member was moved out of Open_tables_state to THD class.
enter_locked_tables_mode()/leave_locked_tables_mode() had to follow.
- Methods of THD responsible for saving/restoring open table state were
changed to use Open_tables_backup class which in addition to
Open_table_state has a member for this savepoint.
Changed Open_table_context class to store MDL_request object for
global intention exclusive lock acquired when opening tables.
sql/sql_delete.cc:
MDL subsystem no longer implicitly acquires global intention exclusive
metadata lock when per-object exclusive metadata lock is acquired.
Now this has to be done by explicit calls outside of MDL subsystem.
sql/sql_help.cc:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. As result code
opening/closing system tables was changed to use Open_tables_backup
instead of Open_table_state class as well.
sql/sql_parse.cc:
Adjusted assert reload_acl_and_cache() to the fact that global read
lock now takes full-blown metadata lock.
sql/sql_plist.h:
Added support for element counting to I_P_List list template.
One can use policy classes to specify if such counting is needed
or not needed for particular list.
sql/sql_show.cc:
Instead of using separate MDL_context for opening tables for I_S
purposes we now create MDL savepoint in the main context before
opening tables and rollback to this savepoint after closing them.
To support this and similar change for system tables methods of
THD responsible for saving/restoring open table state were changed
to use Open_tables_backup class which in addition to Open_table_state
has a member for this savepoint. As result code opening/closing tables
for I_S purposes was changed to use Open_tables_backup instead of
Open_table_state class as well.
sql/sql_table.cc:
mysql_rm_tables_part2():
Since now global intention exclusive metadata lock is ordinary
metadata lock we no longer can rely that by releasing MDL locks
on all tables we will release all locks acquired by this routine.
So in non-LOCK-TABLES mode we have to release all locks acquired
explicitly.
prepare_for_repair(), mysql_alter_table():
MDL subsystem no longer implicitly acquires global intention
exclusive metadata lock when per-object exclusive metadata lock
is acquired. Now this has to be done by explicit calls outside of
MDL subsystem.
sql/tztime.cc:
Instead of using separate MDL_context for opening system tables we now
create MDL savepoint in the main context before opening such tables
and rollback to this savepoint after closing them. To support this
change methods of THD responsible for saving/restoring open table
state were changed to use Open_tables_backup class which in addition
to Open_table_state has a member for this savepoint. As result code
opening/closing system tables was changed to use Open_tables_backup
instead of Open_table_state class as well.
Also changed code not to use special mechanism for open system tables
when it is not really necessary.
Diagnostics_area::set_ok_status at PREPARE
The problem occured during processing of stored routines.
Routines are loaded from mysql.proc, parsed and put into the sp cache by
sp_cache_routine(). The assert occured because the return value from
sp_cache_routine() was not checked for top level CALLs. This meant that any
errors during sp_cache_routine() went unoticed and triggered the assert when
my_ok() was later called.
This is a regression introduced by the patch for Bug#30977, only visible in
source trees with MDL and using debug builds of the server.
This patch fixes the problem by checking the return value from sp_cache_routine()
for top level CALLs and propagating any errors similar to what is done for other
calls to sp_cache_routine().
No test case added.
The problem was that FLUSH TABLE <table_list> would block,
waiting for all tables with old versions to be removed from
the table definition cache, rather than waiting for only
the tables in <table_list>. This could happen if FLUSH TABLE
was used in combination with LOCK TABLES.
With the new MDL code, this problem is no longer repeatable.
Regression test case added to lock.test. This commit contains
no code changes.
This was a deadlock between LOCK TABLES/CREATE DATABASE in one connection
and DROP DATABASE in another. It only happened if the table locked by
LOCK TABLES was in the database to be dropped. The deadlock is similar
to the one in Bug#48940, but with LOCK TABLES instead of an active
transaction.
The order of events needed to trigger the deadlock was:
1) Connection 1 locks table db1.t1 using LOCK TABLES. It will now
have a metadata lock on the table name.
2) Connection 2 issues DROP DATABASE db1. This will wait inside
the MDL subsystem for the lock on db1.t1 to go away. While waiting, it
will hold the LOCK_mysql_create_db mutex.
3) Connection 1 issues CREATE DATABASE (database name irrelevant).
This will hang trying to lock the same mutex. Since this is the connection
holding the metadata lock blocking Connection 2, we have a deadlock.
This deadlock would also happen for earlier trees without MDL, but
there DROP DATABASE would wait for a table to be removed from the
table definition cache.
This patch fixes the problem by prohibiting CREATE DATABASE in LOCK TABLES
mode. In the example above, this prevents Connection 1 from hanging trying
to get the LOCK_mysql_create_db mutex. Note that other commands that use
LOCK_mysql_create_db (ALTER/DROP DATABASE) are already prohibited in
LOCK TABLES mode.
Incompatible change: CREATE DATABASE is now disallowed in LOCK TABLES mode.
Test case added to schema.test.
mysql-test/t/drop.test:
Updates the test for Bug#21216 by swapping the order of CREATE DATABASE
and LOCK TABLES. This is now needed as CREATE DATABASE is prohibited in
LOCK TABLES mode.
mysql-test/t/schema.test:
Test case for Bug#49988 added.
Also fixes a problem with the test for Bug#48940 where the result
would differ for embedded server.
Bug#45523 "Objects of class base_ilist should not be copyable".
Suppress the compiler-generated public copy constructor
and assignment operator of class base_ilist; instead, implement
move_elements_to() function which transfers ownership of elements
from one list to another.
INFILE".
Attempts to execute an INSERT statement for a MEMORY table which invoked
a trigger or called a stored function which tried to perform LOW_PRIORITY
update on the table being inserted into, resulted in debug servers aborting
due to an assertion failure. On non-debug servers such INSERTs failed with
"Can't update table t1 in stored function/trigger because it is already used
by statement which invoked this stored function/trigger" as expected.
The problem was that in the above scenario TL_WRITE_CONCURRENT_INSERT
is converted to TL_WRITE inside the thr_lock() function since the MEMORY
engine does not support concurrent inserts. This triggered an assertion
which assumed that for the same table, one thread always requests locks with
higher thr_lock_type value first. When TL_WRITE_CONCURRENT_INSERT is
upgraded to TL_WRITE after the locks have been sorted, this is no longer true.
In this case, TL_WRITE was requested after acquiring a TL_WRITE_LOW_PRIORITY
lock on the table, triggering the assert.
This fix solves the problem by adjusting this assert to take this
scenario into account.
An alternative approach to change handler::store_locks() methods for all engines
which do not support concurrent inserts in such way that
TL_WRITE_CONCURRENT_INSERT is upgraded to TL_WRITE there instead,
was considered too intrusive.
Commit on behalf of Dmitry Lenev.
mysql-test/r/lock.result:
Added simplified test for bug #48538 "Assertion in thr_lock() on LOAD
DATA CONCURRENT INFILE".
mysql-test/t/lock.test:
Added simplified test for bug #48538 "Assertion in thr_lock() on LOAD
DATA CONCURRENT INFILE".
mysys/thr_lock.c:
Adjusted assertion to account for situation when
TL_WRITE_CONCURRENT_INSERT is converted to TL_WRITE inside of the
thr_lock() function because the engine of the table being locked
does not support concurrent inserts.
This scenario breaks assumption that for the same table one thread
always requests locks with higher thr_lock_type value first, since
TL_WRITE on the table (converted from TL_WRITE_CONCURRENT_INSERT)
can be requested after acquiring a TL_WRITE_LOW_PRIORITY lock on the table.
Note that it is still safe to grant a new lock without extra checks and
waiting in such situation since TL_WRITE has the same compatibility
rules as TL_WRITE_LOW_PRIORITY (their only difference is priority).
This change is supposed to reduce number of ER_LOCK_DEADLOCK
errors which occur when multi-statement transaction encounters
conflicting metadata lock in cases when waiting is possible.
The idea is not to fail ER_LOCK_DEADLOCK error immediately when
we encounter conflicting metadata lock. Instead we release all
metadata locks acquired by current statement and start to wait
until conflicting lock go away. To avoid deadlocks we use simple
empiric which aborts waiting with ER_LOCK_DEADLOCK error if it
turns out that somebody is waiting for metadata locks owned by
this transaction.
This patch also fixes bug #46273 "MySQL 5.4.4 new MDL: Bug#989
is not fully fixed in case of ALTER".
The bug was that concurrent execution of UPDATE or MULTI-UPDATE
statement as a part of multi-statement transaction that already
has used table being updated and ALTER TABLE statement might have
resulted of loss of isolation between this transaction and ALTER
TABLE statement, which manifested itself as changes performed by
ALTER TABLE becoming visible in transaction and wrong binary log
order as a consequence.
This problem occurred when UPDATE or MULTI-UPDATE's wait in
mysql_lock_tables() call was aborted due to metadata lock
upgrade performed by concurrent ALTER TABLE. After such abort all
metadata locks held by transaction were released but transaction
silently continued to be executed as if nothing has happened.
We solve this problem by changing our code not to release all
locks in such case. Instead we release only locks which were
acquired by current statement and then try to reacquire them
by restarting open/lock tables process. We piggyback on simple
deadlock detector implementation since this change has to be
done anyway for it.
mysql-test/include/handler.inc:
After introduction of basic deadlock detector for metadata locks
it became necessary to change parts of test for HANDLER statements
which covered some of scenarios in which ER_LOCK_DEADLOCK error
was detected in absence of real deadlock (with new deadlock detector
this no longer happens).
Also adjusted test to the fact that HANDLER READ for the table no
longer will be blocked by ALTER TABLE for the same table which awaits
for metadata lock upgrade (this is due to removal of mysql_lock_abort()
from wait_while_table_is_used()).
mysql-test/r/handler_innodb.result:
After introduction of basic deadlock detector for metadata locks
it became necessary to change parts of test for HANDLER statements
which covered some of scenarios in which ER_LOCK_DEADLOCK error
was detected in absence of real deadlock (with new deadlock detector
this no longer happens).
Also adjusted test to the fact that HANDLER READ for the table no
longer will be blocked by ALTER TABLE for the same table which awaits
for metadata lock upgrade (this is due to removal of mysql_lock_abort()
from wait_while_table_is_used()).
mysql-test/r/handler_myisam.result:
After introduction of basic deadlock detector for metadata locks
it became necessary to change parts of test for HANDLER statements
which covered some of scenarios in which ER_LOCK_DEADLOCK error
was detected in absence of real deadlock (with new deadlock detector
this no longer happens).
Also adjusted test to the fact that HANDLER READ for the table no
longer will be blocked by ALTER TABLE for the same table which awaits
for metadata lock upgrade (this is due to removal of mysql_lock_abort()
from wait_while_table_is_used()).
mysql-test/r/mdl_sync.result:
Added test coverage for basic deadlock detection in metadata
locking subsystem and for bug #46273 "MySQL 5.4.4 new MDL:
Bug#989 is not fully fixed in case of ALTER".
mysql-test/r/sp-lock.result:
Adjusted test coverage for metadata locking for stored routines
since after introduction of basic deadlock detector for metadata
locks number of scenarios in which ER_LOCK_DEADLOCK error in
absence of deadlock has decreased.
mysql-test/t/mdl_sync.test:
Added test coverage for basic deadlock detection in metadata
locking subsystem and for bug #46273 "MySQL 5.4.4 new MDL:
Bug#989 is not fully fixed in case of ALTER".
mysql-test/t/sp-lock.test:
Adjusted test coverage for metadata locking for stored routines
since after introduction of basic deadlock detector for metadata
locks number of scenarios in which ER_LOCK_DEADLOCK error in
absence of deadlock has decreased.
sql/log_event_old.cc:
close_tables_for_reopen() now takes one more argument which
specifies at which point it should stop releasing metadata
locks acquired by this connection.
sql/mdl.cc:
Changed metadata locking subsystem to support basic deadlock detection
with a help of the following simple empiric -- we assume that there is
a deadlock if there is a connection which has to wait for a metadata
lock which is currently acquired by some connection which is itself
waiting to be able to acquire some shared metadata lock.
To implement this change:
- Added MDL_context::can_wait_lead_to_deadlock()/_impl() methods
which allow to find out if there is someone waiting for metadata
lock which is held by the connection and therefore deadlocks are
possible if this connection is going to wait for some metadata lock.
To do this added version of MDL_ticket::has_pending_conflicting_lock()
method which assumes that its caller already owns LOCK_mdl mutex.
- Changed MDL_context::wait_for_locks() to use one of the above methods
to check if somebody is waiting for metadata lock owned by this
context (and therefore deadlock is possible) and emit ER_LOCK_DEADLOCK
error in this case. Also now we mark context of connections waiting
inside of this method by setting MDL_context::m_is_waiting_in_mdl
member. Thanks to this such connection could be waken up if some
other connection starts waiting for one of its metadata locks and
so a deadlock can occur.
- Adjusted notify_shared_lock() to wake up connections which wait inside
MDL_context::wait_for_locks() while holding shared metadata lock.
- Changed MDL_ticket::upgrade_shared_lock_to_exclusive() to add
temporary ticket for exclusive lock to MDL_lock::waiting queue, so
request for metadata lock upgrade can be properly detected by our
empiric.
Also now this method invokes a callback which forces transactions
holding shared metadata lock on the table to call MDL_context::
can_wait_lead_to_deadlock() method even if they don't need any new
metadata locks. Thanks to this such transactions can detect deadlocks/
livelocks between MDL and table-level locks.
Also reduced timeouts between calls to notify_shared_lock()
in MDL_ticket::upgrade_shared_lock_to_exclusive() and
MDL_context::acquire_exclusive_locks(). This was necessary
to get rid of call to mysql_lock_abort() in wait_while_table_is_used().
(Now we instead rely on notify_shared_lock() timely calling
mysql_lock_abort_for_thread() for the table on which lock
is being upgraded/acquired).
sql/mdl.h:
- Added a version of MDL_ticket::has_pending_conflicting_lock() method
to be used in situations when caller already has acquired LOCK_mdl
mutex.
- Added MDL_context::can_wait_lead_to_deadlock()/_impl() methods
which allow to find out if there is someone waiting for metadata lock
which is held by this connection and thus deadlocks are possible if
this connections will start waiting for some metadata lock.
- Added MDL_context::m_is_waiting_in_mdl member to mark connections
waiting in MDL_context::wait_for_locks() method of metadata locking
subsystem. Added getter method for this private member to make it
accessible in notify_shared_lock() auxiliary so we can wake-up such
connections if they hold shared metadata locks.
- Finally, added mysql_abort_transactions_with_shared_lock() callback
to be able force transactions which don't need any new metadata
locks still call MDL_context::can_wait_lead_to_deadlock() and detect
some of deadlocks between metadata locks and table-level locks.
sql/mysql_priv.h:
close_tables_for_reopen() now takes one more argument which
specifies at which point it should stop releasing metadata
locks acquired by this connection.
sql/sql_base.cc:
Changed approach to metadata locking for multi-statement transactions.
We no longer fail ER_LOCK_DEADLOCK error immediately when we encounter
conflicting metadata lock. Instead we release all metadata locks
acquired by current statement and start to wait until conflicting
locks to go away by calling MDL_context::wait_for_locks() method.
To avoid deadlocks the latter implements simple empiric which aborts
waiting with ER_LOCK_DEADLOCK error if it turns out that somebody
is waiting for metadata locks owned by this transaction.
To implement the change described above:
- Introduced Open_table_context::m_start_of_statement_svp member to
store state of metadata locks at the start of the statement.
- Changed Open_table_context::request_backoff_action() not to
fail with ER_LOCK_DEADLOCK immediately if back-off is requested
due to conflicting metadata lock.
- Added new argument for close_tables_for_reopen() procedure which
allows to specify subset of metadata locks to be released.
- Changed open_tables() not to release all metadata locks acquired
by current transaction when metadata lock conflict is discovered.
Instead we release only locks acquired by current statement.
- Changed open_ltable() and open_and_lock_tables_derived() not to emit
ER_LOCK_DEADLOCK error when mysql_lock_tables() is aborted in
multi-statement transaction when somebody tries to acquire exclusive
metadata lock on the table. Instead we release metadata locks acquired
by current statement and try to wait until they can be re-acquired.
- Adjusted tdc_wait_for_old_versions() to check if there is someone
waiting for one of metadata locks held by this connection and run
deadlock detection in order to avoid deadlocks in some
situations.
- Added mysql_abort_transactions_with_shared_lock() callback which
allows to force transactions holding shared metadata lock on the
table to call MDL_context::can_wait_lead_to_deadlock() even if they
don't need any new metadata locks so they can detect potential
deadlocks between metadata locking subsystem and table-level locks.
- Adjusted wait_while_table_is_used() not to set TABLE::version to
0 as it is now done only when necessary by the above-mentioned
callback. Also removed unnecessary call to mysql_lock_abort().
Instead we rely on code performing metadata lock upgrade aborting
waits on the table-level lock for this table by calling
mysql_lock_abort_for_thread() (invoked by
mysql_notify_thread_having_shared_lock()). In future this should
allow to reduce number of scenarios in which we produce
ER_LOCK_DEADLOCK error even though no real deadlock exists.
sql/sql_class.h:
Introduced Open_table_context::m_start_of_statement_svp member to
store state of metadata locks at the start of the statement.
Replaced Open_table_context::m_can_deadlock member with m_has_locks
member to reflect the fact that we no longer unconditionally emit
ER_LOCK_DEADLOCK error for transaction having some metadata locks
when conflicting metadata lock is discovered.
sql/sql_insert.cc:
close_tables_for_reopen() now takes one more argument which
specifies at which point it should stop releasing metadata
locks acquired by this connection.
sql/sql_plist.h:
Made I_P_List_iterator<T, B> usable with const lists.
sql/sql_show.cc:
close_tables_for_reopen() now takes one more argument which
specifies at which point it should stop releasing metadata
locks acquired by this connection.
sql/sql_update.cc:
Changed UPDATE and MULTI-UPDATE code not to release all metadata
locks when calls to mysql_lock_tables() are aborted. Instead we
release only locks which are acquired by this statement and then
try to reacquire them by calling open_tables(). This solves
bug #46273 "MySQL 5.4.4 new MDL: Bug#989 is not fully fixed in
case of ALTER".
3655 Jon Olav Hauglid 2009-10-19
Bug #30977 Concurrent statement using stored function and DROP FUNCTION
breaks SBR
Bug #48246 assert in close_thread_table
Implement a fix for:
Bug #41804 purge stored procedure cache causes mysterious hang for many
minutes
Bug #49972 Crash in prepared statements
The problem was that concurrent execution of DML statements that
use stored functions and DDL statements that drop/modify the same
function might result in incorrect binary log in statement (and
mixed) mode and therefore break replication.
This patch fixes the problem by introducing metadata locking for
stored procedures and functions. This is similar to what is done
in Bug#25144 for views. Procedures and functions now are
locked using metadata locks until the transaction is either
committed or rolled back. This prevents other statements from
modifying the procedure/function while it is being executed. This
provides commit ordering - guaranteeing serializability across
multiple transactions and thus fixes the reported binlog problem.
Note that we do not take locks for top-level CALLs. This means
that procedures called directly are not protected from changes by
simultaneous DDL operations so they are executed at the state they
had at the time of the CALL. By not taking locks for top-level
CALLs, we still allow transactions to be started inside
procedures.
This patch also changes stored procedure cache invalidation.
Upon a change of cache version, we no longer invalidate the entire
cache, but only those routines which we use, only when a statement
is executed that uses them.
This patch also changes the logic of prepared statement validation.
A stored procedure used by a prepared statement is now validated
only once a metadata lock has been acquired. A version mismatch
causes a flush of the obsolete routine from the cache and
statement reprepare.
Incompatible changes:
1) ER_LOCK_DEADLOCK is reported for a transaction trying to access
a procedure/function that is locked by a DDL operation in
another connection.
2) Procedure/function DDL operations are now prohibited in LOCK
TABLES mode as exclusive locks must be taken all at once and
LOCK TABLES provides no way to specifiy procedures/functions to
be locked.
Test cases have been added to sp-lock.test and rpl_sp.test.
Work on this bug has very much been a team effort and this patch
includes and is based on contributions from Davi Arnaut, Dmitry
Lenev, Magne Mæhre and Konstantin Osipov.
mysql-test/r/ps_ddl.result:
Update results (Bug#30977).
mysql-test/r/ps_ddl1.result:
Update results (Bug#30977).
mysql-test/r/sp-error.result:
Update results (Bug#30977).
mysql-test/r/sp-lock.result:
Update results (Bug#30977).
mysql-test/suite/rpl/r/rpl_sp.result:
Update results (Bug#30977).
mysql-test/suite/rpl/t/rpl_sp.test:
Add a test case for Bug#30977.
mysql-test/t/ps_ddl.test:
Update comments. We no longer re-prepare a prepared statement
when a stored procedure used in top-level CALL is changed.
mysql-test/t/ps_ddl1.test:
Modifying stored procedure p1 no longer invalidates prepared
statement "call p1" -- we can re-use the prepared statement
without invalidation.
mysql-test/t/sp-error.test:
Use a constant for an error value.
mysql-test/t/sp-lock.test:
Add test coverage for Bug#30977.
sql/lock.cc:
Implement lock_routine_name() - a way to acquire an
exclusive metadata lock (ex- name-lock) on
stored procedure/function.
sql/sp.cc:
Change semantics of sp_cache_routine() -- now it has an option
to make sure that the routine that is cached is up to date (has
the latest sp cache version).
Add sp_cache_invalidate() to sp_drop_routine(), where it was
missing (a bug!).
Acquire metadata locks for SP DDL (ALTER/CREATE/DROP). This is
the core of the fix for Bug#30977.
Since caching and cache invalidation scheme was changed, make
sure we don't invalidate the SP cache in the middle of a stored
routine execution. At the same time, make sure we don't access
stale data due to lack of invalidation.
For that, change ALTER FUNCTION/PROCEDURE to not use the cache,
and SHOW PROCEDURE CODE/SHOW CREATE PROCEDURE/FUNCTION to always
read an up to date version of the routine from the cache.
sql/sp.h:
Add a helper wrapper around sp_cache_routine().
sql/sp_cache.cc:
Implement new sp_cache_version() and sp_cache_flush_obsolete().
Now we flush stale routines individually, rather than all at once.
sql/sp_cache.h:
Update signatures of sp_cache_version() and sp_cache_flush_obsolete().
sql/sp_head.cc:
Add a default initialization of sp_head::m_sp_cache_version.
Remove a redundant sp_head::create().
sql/sp_head.h:
Add m_sp_cache_version to sp_head class - we now
keep track of every routine in the stored procedure cache, rather than
of the entire cache.
sql/sql_base.cc:
Implement prelocking for stored routines. Validate stored
routines after they were locked.
Flush obsolete routines upon next access, one by one, not all at once
(Bug#41804).
Style fixes.
sql/sql_class.h:
Rename a Open_table_context method.
sql/sql_parse.cc:
Make sure stored procedures DDL commits the active transaction
(issues an implicit commit before and after).
Remove sp_head::create(), a pure redundancy.
Move the semantical check during alter routine inside sp_update_routine() code in order to:
- avoid using SP cache during update, it may be obsolete.
- speed up and simplify the update procedure.
Remove sp_cache_flush_obsolete() calls, we no longer flush the entire
cache, ever, stale routines are flushed before next use, one at a time.
sql/sql_prepare.cc:
Move routine metadata validation to open_and_process_routine().
Fix Bug#49972 (don't swap flags at reprepare).
Reset Sroutine_hash_entries in reinit_stmt_before_use().
Remove SP cache invalidation, it's now done by open_tables().
sql/sql_show.cc:
Fix a warning: remove an unused label.
sql/sql_table.cc:
Reset mdl_request.ticket for tickets acquired for routines inlined
through a view, in CHECK TABLE statement, to satisfy an MDL assert.
sql/sql_update.cc:
Move the cleanup of "translation items" to close_tables_for_reopen(),
since it's needed in all cases when we back off, not just
the back-off in multi-update. This fixes a bug when the server
would crash on attempt to back off when opening tables
for a statement that uses information_schema tables.
"HANDLER statements within a transaction might lead to deadlocks".
Introduce a notion of a sentinel to MDL_context. A sentinel
is a ticket that separates all tickets in the context into two
groups: before and after it. Currently we can have (and need) only
one designated sentinel -- it separates all locks taken by LOCK
TABLE or HANDLER statement, which must survive COMMIT and ROLLBACK
and all other locks, which must be released at COMMIT or ROLLBACK.
The tricky part is maintaining the sentinel up to date when
someone release its corresponding ticket. This can happen, e.g.
if someone issues DROP TABLE under LOCK TABLES (generally,
see all calls to release_all_locks_for_name()).
MDL_context::release_ticket() is modified to take care of it.
******
A fix and a test case for Bug#46224 "HANDLER statements within a
transaction might lead to deadlocks".
An attempt to mix HANDLER SQL statements, which are transaction-
agnostic, an open multi-statement transaction,
and DDL against the involved tables (in a concurrent connection)
could lead to a deadlock. The deadlock would occur when
HANDLER OPEN or HANDLER READ would have to wait on a conflicting
metadata lock. If the connection that issued HANDLER statement
also had other metadata locks (say, acquired in scope of a
transaction), a classical deadlock situation of mutual wait
could occur.
Incompatible change: entering LOCK TABLES mode automatically
closes all open HANDLERs in the current connection.
Incompatible change: previously an attempt to wait on a lock
in a connection that has an open HANDLER statement could wait
indefinitely/deadlock. After this patch, an error ER_LOCK_DEADLOCK
is produced.
The idea of the fix is to merge thd->handler_mdl_context
with the main mdl_context of the connection, used for transactional
locks. This makes deadlock detection possible, since all waits
with locks are "visible" and available to analysis in a single
MDL context of the connection.
Since HANDLER locks and transactional locks have a different life
cycle -- HANDLERs are explicitly open and closed, and so
are HANDLER locks, explicitly acquired and released, whereas
transactional locks "accumulate" till the end of a transaction
and are released only with COMMIT, ROLLBACK and ROLLBACK TO SAVEPOINT,
a concept of "sentinel" was introduced to MDL_context.
All locks, HANDLER and others, reside in the same linked list.
However, a selected element of the list separates locks with
different life cycle. HANDLER locks always reside at the
end of the list, after the sentinel. Transactional locks are
prepended to the beginning of the list, before the sentinel.
Thus, ROLLBACK, COMMIT or ROLLBACK TO SAVEPOINT, only
release those locks that reside before the sentinel. HANDLER locks
must be released explicitly as part of HANDLER CLOSE statement,
or an implicit close.
The same approach with sentinel
is also employed for LOCK TABLES locks. Since HANDLER and LOCK TABLES
statement has never worked together, the implementation is
made simple and only maintains one sentinel, which is used either
for HANDLER locks, or for LOCK TABLES locks.
mysql-test/include/handler.inc:
Add test coverage for Bug#46224 "HANDLER statements within a
transaction might lead to deadlocks".
Extended HANDLER coverage to cover a mix of HANDLER, transactions
and DDL statements.
mysql-test/r/handler_innodb.result:
Update results (Bug#46224).
mysql-test/r/handler_myisam.result:
Update results (Bug#46224).
sql/lock.cc:
Remove thd->some_tables_deleted, it's never used.
sql/log_event.cc:
No need to check for thd->locked_tables_mode,
it's done inside release_transactional_locks().
sql/mdl.cc:
Implement the concept of HANDLER and LOCK TABLES "sentinel".
Implement a method to clone an acquired ticket.
Do not return tickets beyond the sentinel when acquiring
locks, create a copy.
Remove methods to merge and backup MDL_context, they are now
not used (Hurra!). This opens a path to a proper constructor
and destructor of class MDL_context (to be done in a separate
patch).
Modify find_ticket() to provide information about where
the ticket position is with regard to the sentinel.
sql/mdl.h:
Add declarations necessary for the implementation of the concept
of "sentinel", a dedicated ticket separating transactional and
non-transactional locks.
sql/mysql_priv.h:
Add mark_tmp_table_for_reuse() declaration,
a function to "close" a single session (temporary) table.
sql/sql_base.cc:
Remove thd->some_tables_deleted.
Modify deadlock-prevention asserts and deadlock detection
heuristics to take into account that from now on HANDLER locks
reside in the same locking context.
Add broadcast_refresh() to mysql_notify_thread_having_shared_lock():
this is necessary for the case when a thread having a shared lock
is asleep in tdc_wait_for_old_versions(). This situation is only
possible with HANDLER t1 OPEN; FLUSH TABLE (since all over code paths
that lead to tdc_wait_for_old_versions() always have an
empty MDL_context). Previously the server would simply deadlock
in this situation.
sql/sql_class.cc:
Remove now unused member "THD::some_tables_deleted".
Move mysql_ha_cleanup() a few lines above in THD::cleanup()
to make sure that all handlers are closed when it's time to
destroy the MDL_context of this connection.
Remove handler_mdl_context and handler_tables.
sql/sql_class.h:
Remove THD::handler_tables, THD::handler_mdl_context,
THD::some_tables_deleted.
sql/sql_handler.cc:
Remove thd->handler_tables.
Remove thd->handler_mdl_context.
Rewrite mysql_ha_open() to have no special provision for MERGE
tables, now that we don't have to manipulate with thd->handler_tables
it's easy to do.
Remove dead code.
Fix a bug in mysql_ha_flush() when we would always flush
a temporary HANDLER when mysql_ha_flush() is called (actually
mysql_ha_flush() never needs to flush temporary tables).
sql/sql_insert.cc:
Update a comment, no more thd->some_tables_deleted.
sql/sql_parse.cc:
Implement an incompatible change: entering LOCK TABLES closes
active HANDLERs, if any.
Now that we have a sentinel, we don't need to check
for thd->locked_tables_mode when releasing metadata locks in
COMMIT/ROLLBACK.
sql/sql_plist.h:
Add new (now necessary) methods to the list class.
sql/sql_prepare.cc:
Make sure we don't release HANDLER locks when rollback to a
savepoint, set to not keep locks taken at PREPARE.
sql/sql_servers.cc:
Update to a new signature of MDL_context::release_all_locks().
sql/sql_table.cc:
Remove thd->some_tables_deleted.
sql/transaction.cc:
Add comments.
Make sure rollback to (MDL) savepoint works under LOCK TABLES and
with HANDLER tables.
------------------------------------------------------------
revno: 2617.14.26
committer: Vladislav Vaintroub <vvaintroub@mysql.com>
branch nick: mysql-6.0-wtf
timestamp: Wed 2008-11-05 11:19:19 +0100
message:
CMakeLists.txt files cleanup.
- remove SAFEMALLOC and SAFE_MUTEX definitions that were
present in *each* CMakeLists.txt. Instead, put them into top level
MakeLists.txt, but disable on Windows, because
a) SAFEMALLOC does not add any functionality that is not already
present in Debug C runtime ( and 2 safe malloc one on top of the other
only unnecessarily slows down the server)
b)SAFE_MUTEX does not work on Windows and have been
explicitely disabled on Windows with #undef previously. Fortunately,
ntdll does pretty good job identifying l problems with CRITICAL_SECTIONs.
(DebugBreak()s on using uninited critical section, unlocking unowned
critical section)
-Remove occationally used -D_DEBUG (added by compiler
anyway)
-Remove MAP file generation, it became obsolete .
There are many ways to get callstack of a crash now, with stacktrace in
error log , minidump etc
The test allowed random coincidence of connection ids for two concurrent
sessions performing CREATE/DROP temp tables.
Fixed with correcting the test. The sessions connection ids are not changed
from their defaults anymore.
If the handler (or delayed insert) thread failed to lock a table due
to being killed, the "dead" flag was used to notify the connection thread
of this failure. However, with the changes introduced by Bug#45949,
the handler thread will no longer try to lock the table if it was killed.
This meant that the "dead" flag would not be set, and the connection
thread would not notice that the handler thread had failed.
This could happen with concurrent INSERT DELAYED and FLUSH TABLES.
FLUSH TABLES would kill any active INSERT DELAYED that had opened any
table(s) to be flushed. This could cause the INSERT DELAYED connection
thread to be stuck waiting for the handler thread to lock its table,
while the handler thread would be looping, trying to get the connection
thread to notice the error.
The root of the problem was that the handler thread had both the "dead"
flag and "thd->killed" to indicate that it had been killed. Most places
both were set, but some only set "thd->killed". And
Delayed_insert::get_local_table() only checked "dead" while waiting for
the table to be locked.
This patch removes the "dead" variable and replaces its usage with
"thd->killed", thereby resolving the issue.
When compressed myisam files are opened, they are always memory mapped
sometimes causing memory swapping problems.
When we mmap the myisam compressed tables of size greater than the memory
available, the kswapd0 process utilization is very high consuming 30-40% of
the cpu. This happens only with linux kernels older than 2.6.9
With newer linux kernels, we don't have this problem of high cpu consumption
and this option may not be required.
The option 'myisam_mmap_size' is added to limit the amount of memory used for
memory mapping of myisam files. This option is not dynamic.
The default value on 32 bit system is 4294967295 bytes and on 64 bit system it
is 18446744073709547520 bytes.
Note: Testcase only tests the option variable. The actual bug has be to
tested manually.
include/my_global.h:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
define SIZE_T_MAX
include/myisam.h:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
declare 'myisam_mmap_size' and 'myisam_mmap_used' variables and the mutex
THR_LOCK_myisam_mmap
myisam/mi_packrec.c:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
add 'myisam_mmap_size' option which limits the memory available to mmap of
myisam files
myisam/mi_static.c:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
declare 'myisam_mmap_size' and 'myisam_mmap_used' variables and the mutex
THR_LOCK_myisam_mmap
myisam/myisamdef.h:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
move MEMMAP_EXTRA_MARGIN to myisam.h so that it can be used in mysqld.cc
mysql-test/r/variables.result:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
Testcase for BUG#37408 to test the myisam_mmap_size option
mysql-test/t/variables.test:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
Testcase for BUG#37408 to test the myisam_mmap_size option
mysys/my_thr_init.c:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
intialize the lock THR_LOCK_myisam_mmap
sql/mysqld.cc:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
add the 'myisam_mmap_size' option
sql/set_var.cc:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
add the 'myisam_mmap_size' to the SHOW VARIABLES list
returns incorrect results with where
An outer join of a const table (outer) and a normal table
(inner) with GROUP BY on a field from the outer table would
optimize away GROUP BY, and thus trigger the optimization to
do away with a temporary table if grouping was performed on
columns from the const table, hence executing the query with
filesort without temporary table. But this should not be
done if there is a non-indexed access to the inner table,
since filesort does not handle joins. It expects either ref
access, range ditto or table scan. The join condition will
thus not be applied.
Fixed by always forcing execution with temporary table in
the case of ROLLUP with a query involving an outer join. This
is a slightly broader class of queries than need fixing, but
it is hard to ascertain the position of a ROLLUP field wrt
outer join with current query representation.
mysql-test/r/join_outer.result:
Bug#47650: Test result
mysql-test/t/join_outer.test:
Bug#47650: Test case
sql/sql_select.cc:
Bug#47650: Fix
Problem: inserting a record we don't set unused null bits in the
record buffer if no default field values used.
That may lead to wrong live checksum calculation.
Fix: set unused null bits in the record buffer in such cases.
mysql-test/r/myisam.result:
Fix for bug#49465: valgrind warnings and incorrect live checksum...
- test result.
mysql-test/t/myisam.test:
Fix for bug#49465: valgrind warnings and incorrect live checksum...
- test case.
sql/sql_insert.cc:
Fix for bug#49465: valgrind warnings and incorrect live checksum...
- set unused null bits to 1 in the record buffer in case we
don't call restore_record() before a fill_record() call
(when no default values used).
The bug is caused by a race condition between the
INSERT DELAYED thread and the client thread's FLUSH TABLE. The
FLUSH TABLE does not guarantee (as is (wrongly) suggested in the
test case) that the INSERT DELAYED is ever executed. The
execution of the test case will thus not be deterministic.
The fix has been to do a deterministic verification that both
threads are complete by checking the content of the table.
