newly introduced metadata locks.
Previously the behavior was deterministic and if several LOCKs were
waiting the first one of them was released by UNLOCK (in chronological
order).
Now (with MDLs) the behavior is undefined and since we do not know in
what order to --reap the connections we simply disconnect them without
reaping.
------------------------------------------------------------
revno: 2875.107.114
revision-id: dlenev@mysql.com-20100201114306-cve0yq5akrxjoei0
parent: dlenev@mysql.com-20100121204303-sr6d1436mac7x6vz
committer: Dmitry Lenev <dlenev@mysql.com>
branch nick: mysql-next-4284-nl-push
timestamp: Mon 2010-02-01 14:43:06 +0300
message:
Implement new type-of-operation-aware metadata locks.
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.
Conflicts:
Text conflict in client/mysqlbinlog.cc
Text conflict in mysql-test/Makefile.am
Text conflict in mysql-test/collections/default.daily
Text conflict in mysql-test/r/mysqlbinlog_row_innodb.result
Text conflict in mysql-test/suite/rpl/r/rpl_typeconv_innodb.result
Text conflict in mysql-test/suite/rpl/t/rpl_get_master_version_and_clock.test
Text conflict in mysql-test/suite/rpl/t/rpl_row_create_table.test
Text conflict in mysql-test/suite/rpl/t/rpl_slave_skip.test
Text conflict in mysql-test/suite/rpl/t/rpl_typeconv_innodb.test
Text conflict in mysys/charset.c
Text conflict in sql/field.cc
Text conflict in sql/field.h
Text conflict in sql/item.h
Text conflict in sql/item_func.cc
Text conflict in sql/log.cc
Text conflict in sql/log_event.cc
Text conflict in sql/log_event_old.cc
Text conflict in sql/mysqld.cc
Text conflict in sql/rpl_utility.cc
Text conflict in sql/rpl_utility.h
Text conflict in sql/set_var.cc
Text conflict in sql/share/Makefile.am
Text conflict in sql/sql_delete.cc
Text conflict in sql/sql_plugin.cc
Text conflict in sql/sql_select.cc
Text conflict in sql/sql_table.cc
Text conflict in storage/example/ha_example.h
Text conflict in storage/federated/ha_federated.cc
Text conflict in storage/myisammrg/ha_myisammrg.cc
Text conflict in storage/myisammrg/myrg_open.c
Problem: caseup_multiply and casedn_multiply members
were not initialized for a dynamic collation, so
UPPER() and LOWER() functions returned empty strings.
Fix: initializing the members properly.
Adding tests:
mysql-test/r/ctype_ldml.result
mysql-test/t/ctype_ldml.test
Applying the fix:
mysys/charset.c
(Original patch by Sinisa Milivojevic)
The YEAR(4) value of 2000 was equal to the "bad" YEAR(4) value of 0000.
The get_year_value() function has been modified to not adjust bad
YEAR(4) value to 2000.
mysql-test/r/type_year.result:
Test case for bug #49910.
mysql-test/t/type_year.test:
Test case for bug #49910.
sql/item_cmpfunc.cc:
Bug #49910: Behavioural change in SELECT/WHERE on YEAR(4) data type
The get_year_value() function has been modified to not adjust bad
YEAR(4) value to 2000.
Conflicts:
Text conflict in mysql-test/r/partition_innodb.result
Text conflict in sql/field.h
Text conflict in sql/item.h
Text conflict in sql/item_cmpfunc.h
Text conflict in sql/item_sum.h
Text conflict in sql/log_event_old.cc
Text conflict in sql/protocol.cc
Text conflict in sql/sql_select.cc
Text conflict in sql/sql_yacc.yy
The problem is that when we make conditon for
grouped result const part of condition is cut off.
It happens because some parts of 'having' condition
which refer to outer join become const after
make_join_statistics. These parts may be lost
during further having condition transformation
in JOIN::exec. The fix is adding 'having'
condition check for const tables after
make_join_statistics is performed.
mysql-test/r/having.result:
test case
mysql-test/t/having.test:
test result
sql/sql_select.cc:
added 'having' condition check for const tables
after make_join_statistics is performed.
DBUG_SYNC_POINT has at least one strong limitation that it's not defined
on all platforms. It has issues cooperating with @@debug.
All in all its functionality is superseded by DEBUG_SYNC facility and
there is no reason to maintain the old less flexible one.
Fixed with adding debug_sync_set_action() function as a facility to set up
a sync-action in the server sources code and re-writing existing simulations
(found 3) to use it.
Couple of tests have been reworked as well.
The patch offers a pattern for setting sync-points in replication threads
where the standard DEBUG_SYNC does not suffice to reach goals.
mysql-test/extra/rpl_tests/rpl_get_master_version_and_clock.test:
rewriting the test from GET_LOCK()-based to DEBUG_SYNC-based;
a pattern of usage DEBUG_SYNC for replication testing is provided.
mysql-test/suite/rpl/r/rpl_get_master_version_and_clock.result:
results are changed.
mysql-test/suite/rpl/t/rpl_get_master_version_and_clock.test:
rewriting the test from GET_LOCK()-based to DEBUG_SYNC-based;
limiting the test to run only with MIXED binlog-format as the test last
some 10 secs sensitively contributing to the total of tests run.
mysql-test/suite/rpl/t/rpl_show_slave_running.test:
rewriting the test from GET_LOCK()-based to DEBUG_SYNC-based.
sql/debug_sync.cc:
adding debug_sync_set_action() function as a facility to set up
a sync-action in the server sources code.
sql/debug_sync.h:
externalizing debug_sync_set_action().
sql/item_func.cc:
purging sources from DBUG_SYNC_POINT.
sql/mysql_priv.h:
purging sources from DBUG_SYNC_POINT.
sql/slave.cc:
rewriting failure simulations to base on DEBUG_SYNC rather than GET_LOCK()-based DBUG_SYNC_POINT.
sql/sql_repl.cc:
removing an orphan failure simulation line because no counterpart in tests existing.
This has been back-ported from 6.0 as the problems proved to afflict
5.1 as well.
The fix exposed two new bugs. They were reported as follows.
Bug no 52174: Sometimes wrong plan when reading a MAX value
from non-NULL index
Bug no 52173: Reading NULL value from non-NULL index gives wrong
result in embedded server
Both bugs taken together affect a much smaller class of queries than #47762,
so the fix stays for now.
Optimizer erroneously translated LEFT JOIN into INNER JOIN.
It leads to cutting rows with NULL right side. It happens
because Item_row uses not_null_tables() method form the
base(Item) class and does not calculate 'null tables'
properly. The fix is adding calculation of 'not null tables'
to Item_row.
mysql-test/r/join_outer.result:
test result
mysql-test/t/join_outer.test:
test case
sql/item_row.cc:
adding calculation of 'not null tables' to Item_row.
sql/item_row.h:
adding calculation of 'not null tables' to Item_row.
The crash happens because of discrepancy between values of
conts_tables and join->const_table_map(make_join_statisctics).
Calculation of conts_tables used condition with
HA_STATS_RECORDS_IS_EXACT flag check. Calculation of
join->const_table_map does not use this flag check.
In case of MERGE table without union with index
the table does not become const table and
thus join_read_const_table() is not called
for the table. join->const_table_map supposes
this table is const and later in make_join_select
this table is used for making&calculation const
condition. As table record buffer is not populated
it leads to crash.
The fix is adding a check if an engine supports
HA_STATS_RECORDS_IS_EXACT flag before updating
join->const_table_map.
mysql-test/r/merge.result:
test result
mysql-test/t/merge.test:
test case
sql/sql_select.cc:
adding a check if an engine supports
HA_STATS_RECORDS_IS_EXACT flag before updating
join->const_table_map.
All numeric operators and functions on integer, floating point
and DECIMAL values now throw an 'out of range' error rather
than returning an incorrect value or NULL, when the result is
out of supported range for the corresponding data type.
Some test cases in the test suite had to be updated
accordingly either because the test case itself relied on a
value returned in case of a numeric overflow, or because a
numeric overflow was the root cause of the corresponding bugs.
The latter tests are no longer relevant, since the expressions
used to trigger the corresponding bugs are not valid anymore.
However, such test cases have been adjusted and kept "for the
record".
mysql-test/r/func_math.result:
Added test cases for bug #8433.
Updated results of the test case for bug #31236.
mysql-test/r/func_misc.result:
Streamlined test cases.
mysql-test/r/func_test.result:
Streamlined test cases.
mysql-test/r/select.result:
Streamlined test cases.
mysql-test/r/sp.result:
Streamlined test cases.
mysql-test/r/strict.result:
Streamlined test cases.
mysql-test/r/type_newdecimal.result:
Streamlined test cases.
mysql-test/suite/sys_vars/r/sql_slave_skip_counter_basic.result:
Streamlined test cases.
mysql-test/suite/sys_vars/t/sql_slave_skip_counter_basic.test:
Streamlined test cases.
mysql-test/t/func_math.test:
Added test cases for bug #8433.
Updated results of the test case for bug #31236.
mysql-test/t/func_misc.test:
Streamlined test cases.
mysql-test/t/func_test.test:
Streamlined test cases.
mysql-test/t/select.test:
Streamlined test cases.
mysql-test/t/sp.test:
Streamlined test cases.
mysql-test/t/strict.test:
Streamlined test cases.
mysql-test/t/type_newdecimal.test:
Streamlined test cases.
sql/item_create.cc:
Changed Item_func_cot() to be defined as a standalone Item
rather than a combination of "1 / TAN(x)".
sql/item_func.cc:
Throw an 'out of range' error rather than returning an
incorrect value or NULL, when the result of a numeric
operator or a function is out of supported range for
the corresponding data type.
sql/item_func.h:
Added validation helpers as inline methods of Item_func.
sql/share/errmsg-utf8.txt:
New ER_DATA_OUT_OF_RANGE error.
