mariadb

Tree: c5317dfb67

Author	SHA1	Message	Date
Jon Olav Hauglid	4347e302a8	Bug #51391 Deadlock involving events during rqg_info_schema test This was a deadlock between CREATE/ALTER/DROP EVENT and a query accessing both the mysql.event table and I_S.GLOBAL_VARIABLES. The root of the problem was that the LOCK_event_metadata mutex was used to both protect the "event_scheduler" global system variable and the internal event data structures used by CREATE/ALTER/DROP EVENT. The deadlock would occur if CREATE/ALTER/DROP EVENT held LOCK_event_metadata while trying to open the mysql.event table, at the same time as the query had mysql.event open, trying to lock LOCK_event_metadata to access "event_scheduler". This bug was fixed in the scope of Bug#51160 by using only LOCK_global_system_variables to protect "event_scheduler". This makes it so that the query above won't lock LOCK_event_metadata, thereby preventing this deadlock from occuring. This patch contains no code changes. Test case added to lock_sync.test.	16 years ago
Konstantin Osipov	e6cb88eb74	next-4284 tree: fix lock_sync.test failure in row based replication mode.	16 years ago
Jon Olav Hauglid	a19377e0d7	Bug #50821 Deadlock between LOCK TABLES and ALTER TABLE This was a deadlock between ALTER TABLE and another DML statement (or LOCK TABLES ... READ). ALTER TABLE would wait trying to upgrade its lock to MDL_EXCLUSIVE and the DML statement would wait trying to acquire a TL_READ_NO_INSERT table level lock. This could happen if one connection first acquired a MDL_SHARED_READ lock on a table. In another connection ALTER TABLE is then started. ALTER TABLE eventually blocks trying to upgrade to MDL_EXCLUSIVE, but while holding a TL_WRITE_ALLOW_READ table level lock. If the first connection then tries to acquire TL_READ_NO_INSERT, it will block and we have a deadlock since neither connection can proceed. This patch fixes the problem by allowing TL_READ_NO_INSERT locks to be granted if another connection holds TL_WRITE_ALLOW_READ on the same table. This will allow the DML statement to proceed such that it eventually can release its MDL lock which in turn makes ALTER TABLE able to proceed. Note that TL_READ_NO_INSERT was already partially compatible with TL_WRITE_ALLOW_READ as the latter would be granted if the former lock was held. This patch just makes the opposite true as well. Also note that since ALTER TABLE takes an upgradable MDL lock, there will be no starvation of ALTER TABLE statements by statements acquiring TL_READ or TL_READ_NO_INSERT. Test case added to lock_sync.test.	16 years ago
Dmitry Lenev	eba5d30e67	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.	16 years ago
Konstantin Osipov	cd155be564	Backport of: ------------------------------------------------------------ revno: 3035.4.1 committer: Davi Arnaut <Davi.Arnaut@Sun.COM> branch nick: 39897-6.0 timestamp: Thu 2009-01-15 12:17:57 -0200 message: Bug#39897: lock_multi fails in pushbuild: timeout waiting for processlist The problem is that relying on the "Table lock" thread state in its current position to detect that a thread is waiting on a lock is race prone. The "Table lock" state change happens before the thread actually tries to grab a lock on a table. The solution is to move the "Table lock" state so that its set only when a thread is actually going to wait for a lock. The state change happens after the thread fails to grab the lock (because it is owned by other thread) and proceeds to wait on a condition. This is considered part of work related to WL#4284 "Transactional DDL locking" Warning: this patch contains an incompatible change. When waiting on a lock in thr_lock.c, the server used to display "Locked" processlist state. After this patch, the state is "Table lock". The new state was actually intended to be display since year 2002, when Monty added it. But up until removal of thd->locked boolean member, this state was ignored by SHOW PROCESSLIST code. mysql-test/r/lock_multi.result: A style fix. mysql-test/r/sp-threads.result: Changed output of SHOW PROCESSLIST (new wait state). mysql-test/t/lock_multi.test: Use a more accurate state description when waiting inside thr_lock.c. mysql-test/t/lock_sync.test: Use a more accurate state description when waiting inside thr_lock.c. mysql-test/t/multi_update.test: Use a more accurate state description when waiting inside thr_lock.c. mysql-test/t/query_cache_28249.test: Use a more accurate state description when waiting inside thr_lock.c. mysql-test/t/sp_notembedded.test: Use a more accurate state description when waiting inside thr_lock.c. mysql-test/t/status.test: Use a more accurate state description when waiting inside thr_lock.c. mysys/thr_lock.c: Update thread state while waiting for a table lock. sql/lock.cc: State change was moved inside thr_lock.c.	16 years ago
Dmitry Lenev	1e5804f2c5	Fixed lock_sync.test failure in mysql-next-mr tree in embedded mode. Disabled execution of this test for embedded server until fix for bug 41971 'Thread state on embedded server is always "Writing to net"' is back-ported to this tree.	16 years ago
Dmitry Lenev	86c23fa708	Fix for bug #45143 "All connections hang on concurrent ALTER TABLE". Concurrent execution of statements which require non-table-level write locks on several instances of the same table (such as SELECT ... FOR UPDATE which uses same InnoDB table twice or a DML statement which invokes trigger which tries to update same InnoDB table directly and through stored function) and statements which required table-level locks on this table (e.g. LOCK TABLE ... WRITE, ALTER TABLE, ...) might have resulted in a deadlock. The problem occured when a thread tried to acquire write lock (TL_WRITE_ALLOW_WRITE) on the table but had to wait since there was a pending write lock (TL_WRITE, TL_WRITE_ALLOW_READ) on this table and we failed to detect that this thread already had another instance of write lock on it (so in fact we were trying to acquire recursive lock) because there was also another thread holding write lock on the table (also TL_WRITE_ALLOW_WRITE). When the latter thread released its lock neither the first thread nor the thread trying to acquire TL_WRITE/TL_WRITE_ALLOW_READ were woken up (as table was still write locked by the first thread) so we ended up with a deadlock. This patch solves this problem by ensuring that thread which already has write lock on the table won't wait when it tries to acquire second write lock on the same table. mysql-test/r/lock_sync.result: Added test case for bug #45143 "All connections hang on concurrent ALTER TABLE". mysql-test/t/lock_sync.test: Added test case for bug #45143 "All connections hang on concurrent ALTER TABLE". mysys/thr_lock.c: Ensured that thread can acquire write lock on the table without waiting if it already has write lock on it even if there are other threads holding write locks on this table (this is normal situation for, e.g., TL_WRITE_ALLOW_WRITE type of lock). Adjusted comments to better explain why it is OK to do so and added asserts to prevent introduction of scenarios in which this can cause problems.	16 years ago

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