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  1. 12 Jan, 2011 1 commit
    • Davi Arnaut's avatar
      Bug#42054: SELECT CURDATE() is returning bad value · 7ba98a4a
      Davi Arnaut authored
      The problem from a user point of view was that on Solaris the
      time related functions (e.g. NOW(), SYSDATE(), etc) would always
      return a fixed time.
      
      This bug was happening due to a logic in the time retrieving
      wrapper function which would only call the time() function every
      half second. This interval between calls would be calculated
      using the gethrtime() and the logic relied on the fact that time
      returned by it is monotonic.
      
      Unfortunately, due to bugs in the gethrtime() implementation,
      there are some cases where the time returned by it can drift
      (See Solaris bug id 6600939), potentially causing the interval
      calculation logic to fail.
      
      Since newer versions of Solaris (10+) have alleviated the
      performance degradation associated with time(2), the solution is
      to simply directly rely on time() at each invocation.
      
      This simplification has an upside that it allows us to eliminate
      a lock which was used to control access to the variables used
      to track the half second interval, thus improving the overall
      scalability of timekeeping related functions (e.g. NOW()).
      
      Benchmarks runs have shown no significant degradation associated
      with this change. With this, there are actually improvements in
      performance for cases involving many connections.
      
      In summary, the changes introduced by this patch are:
      
      a) my_time() and my_micro_time_and_time() no longer use gethrtime().
         Instead, time() and gettimeofdate() are used correspondingly.
      
      b) my_micro_time() is changed to not use gethrtime() so as to
         have the same time source as my_micro_time_and_time().
         There shouldn't be any performance impact from this change
         since this function is used only a few times during statement
         execution and, on Solaris, gettimeofday() shows acceptable
         performance.
      
      mysys/my_getsystime.c:
        Use time() even if gethrtime() is available. Remove logic which
        relied on gethrtime() to only call time() every half second.
        Since gethrtime() is not used anymore, also remove it from
        my_micro_time() to keep a common time source.
        
        Also, function comments are cleaned up (fixed typos and wrong
        information) and converted to doxygen.
      mysys/my_thr_init.c:
        Remove mutex which is no longer used.
      mysys/mysys_priv.h:
        Remove mutex which is no longer used.
      7ba98a4a
  2. 11 Nov, 2010 1 commit
    • Dmitry Lenev's avatar
      Patch that refactors global read lock implementation and fixes · 730c3cdc
      Dmitry Lenev authored
      bug #57006 "Deadlock between HANDLER and FLUSH TABLES WITH READ
      LOCK" and bug #54673 "It takes too long to get readlock for
      'FLUSH TABLES WITH READ LOCK'".
      
      The first bug manifested itself as a deadlock which occurred
      when a connection, which had some table open through HANDLER
      statement, tried to update some data through DML statement
      while another connection tried to execute FLUSH TABLES WITH
      READ LOCK concurrently.
      
      What happened was that FTWRL in the second connection managed
      to perform first step of GRL acquisition and thus blocked all
      upcoming DML. After that it started to wait for table open
      through HANDLER statement to be flushed. When the first connection
      tried to execute DML it has started to wait for GRL/the second
      connection creating deadlock.
      
      The second bug manifested itself as starvation of FLUSH TABLES
      WITH READ LOCK statements in cases when there was a constant
      stream of concurrent DML statements (in two or more
      connections).
      
      This has happened because requests for protection against GRL
      which were acquired by DML statements were ignoring presence of
      pending GRL and thus the latter was starved.
      
      This patch solves both these problems by re-implementing GRL
      using metadata locks.
      
      Similar to the old implementation acquisition of GRL in new
      implementation is two-step. During the first step we block
      all concurrent DML and DDL statements by acquiring global S
      metadata lock (each DML and DDL statement acquires global IX
      lock for its duration). During the second step we block commits
      by acquiring global S lock in COMMIT namespace (commit code
      acquires global IX lock in this namespace).
      
      Note that unlike in old implementation acquisition of
      protection against GRL in DML and DDL is semi-automatic.
      We assume that any statement which should be blocked by GRL
      will either open and acquires write-lock on tables or acquires
      metadata locks on objects it is going to modify. For any such
      statement global IX metadata lock is automatically acquired
      for its duration.
      
      The first problem is solved because waits for GRL become
      visible to deadlock detector in metadata locking subsystem
      and thus deadlocks like one in the first bug become impossible.
      
      The second problem is solved because global S locks which
      are used for GRL implementation are given preference over
      IX locks which are acquired by concurrent DML (and we can
      switch to fair scheduling in future if needed).
      
      Important change:
      FTWRL/GRL no longer blocks DML and DDL on temporary tables.
      Before this patch behavior was not consistent in this respect:
      in some cases DML/DDL statements on temporary tables were
      blocked while in others they were not. Since the main use cases
      for FTWRL are various forms of backups and temporary tables are
      not preserved during backups we have opted for consistently
      allowing DML/DDL on temporary tables during FTWRL/GRL.
      
      Important change:
      This patch changes thread state names which are used when
      DML/DDL of FTWRL is waiting for global read lock. It is now
      either "Waiting for global read lock" or "Waiting for commit
      lock" depending on the stage on which FTWRL is.
      
      Incompatible change:
      To solve deadlock in events code which was exposed by this
      patch we have to replace LOCK_event_metadata mutex with
      metadata locks on events. As result we have to prohibit
      DDL on events under LOCK TABLES.
      
      This patch also adds extensive test coverage for interaction
      of DML/DDL and FTWRL.
      
      Performance of new and old global read lock implementations
      in sysbench tests were compared. There were no significant
      difference between new and old implementations.
      
      mysql-test/include/check_ftwrl_compatible.inc:
        Added helper script which allows to check that a statement is
        compatible with FLUSH TABLES WITH READ LOCK.
      mysql-test/include/check_ftwrl_incompatible.inc:
        Added helper script which allows to check that a statement is
        incompatible with FLUSH TABLES WITH READ LOCK.
      mysql-test/include/handler.inc:
        Adjusted test case to the fact that now DROP TABLE closes
        open HANDLERs for the table to be dropped before checking
        if there active FTWRL in this connection.
      mysql-test/include/wait_show_condition.inc:
        Fixed small error in the timeout message. The correct name
        of variable used as parameter for this script is "$condition"
        and not "$wait_condition".
      mysql-test/r/delayed.result:
        Added test coverage for scenario which triggered assert in
        metadata locking subsystem.
      mysql-test/r/events_2.result:
        Updated test results after prohibiting event DDL operations
        under LOCK TABLES.
      mysql-test/r/flush.result:
        Added test coverage for bug #57006 "Deadlock between HANDLER
        and FLUSH TABLES WITH READ LOCK".
      mysql-test/r/flush_read_lock.result:
        Added test coverage for various aspects of FLUSH TABLES WITH
        READ LOCK functionality.
      mysql-test/r/flush_read_lock_kill.result:
        Adjusted test case after replacing custom global read lock
        implementation with one based on metadata locks. Use new
        debug_sync point. Do not disable concurrent inserts as now
        InnoDB we always use InnoDB table.
      mysql-test/r/handler_innodb.result:
        Adjusted test case to the fact that now DROP TABLE closes
        open HANDLERs for the table to be dropped before checking
        if there active FTWRL in this connection.
      mysql-test/r/handler_myisam.result:
        Adjusted test case to the fact that now DROP TABLE closes
        open HANDLERs for the table to be dropped before checking
        if there active FTWRL in this connection.
      mysql-test/r/mdl_sync.result:
        Adjusted test case after replacing custom global read lock
        implementation with one based on metadata locks. Replaced
        usage of GRL-specific debug_sync's with appropriate sync
        points in MDL subsystem.
      mysql-test/suite/perfschema/r/dml_setup_instruments.result:
        Updated test results after removing global
        COND_global_read_lock condition variable.
      mysql-test/suite/perfschema/r/func_file_io.result:
        Ensure that this test doesn't affect subsequent tests.
        At the end of its execution enable back P_S instrumentation
        which this test disables at some point.
      mysql-test/suite/perfschema/r/func_mutex.result:
        Ensure that this test doesn't affect subsequent tests.
        At the end of its execution enable back P_S instrumentation
        which this test disables at some point.
      mysql-test/suite/perfschema/r/global_read_lock.result:
        Adjusted test case to take into account that new GRL
        implementation is based on MDL.
      mysql-test/suite/perfschema/r/server_init.result:
        Adjusted test case after replacing custom global read
        lock implementation with one based on MDL and replacing
        LOCK_event_metadata mutex with metadata lock.
      mysql-test/suite/perfschema/t/func_file_io.test:
        Ensure that this test doesn't affect subsequent tests.
        At the end of its execution enable back P_S instrumentation
        which this test disables at some point.
      mysql-test/suite/perfschema/t/func_mutex.test:
        Ensure that this test doesn't affect subsequent tests.
        At the end of its execution enable back P_S instrumentation
        which this test disables at some point.
      mysql-test/suite/perfschema/t/global_read_lock.test:
        Adjusted test case to take into account that new GRL
        implementation is based on MDL.
      mysql-test/suite/perfschema/t/server_init.test:
        Adjusted test case after replacing custom global read
        lock implementation with one based on MDL and replacing
        LOCK_event_metadata mutex with metadata lock.
      mysql-test/suite/rpl/r/rpl_tmp_table_and_DDL.result:
        Updated test results after prohibiting event DDL under
        LOCK TABLES.
      mysql-test/t/delayed.test:
        Added test coverage for scenario which triggered assert in
        metadata locking subsystem.
      mysql-test/t/events_2.test:
        Updated test case after prohibiting event DDL operations
        under LOCK TABLES.
      mysql-test/t/flush.test:
        Added test coverage for bug #57006 "Deadlock between HANDLER
        and FLUSH TABLES WITH READ LOCK".
      mysql-test/t/flush_block_commit.test:
        Adjusted test case after changing thread state name which
        is used when COMMIT waits for FLUSH TABLES WITH READ LOCK
        from "Waiting for release of readlock" to "Waiting for commit
        lock".
      mysql-test/t/flush_block_commit_notembedded.test:
        Adjusted test case after changing thread state name which is
        used when DML waits for FLUSH TABLES WITH READ LOCK. Now we
        use "Waiting for global read lock" in this case.
      mysql-test/t/flush_read_lock.test:
        Added test coverage for various aspects of FLUSH TABLES WITH
        READ LOCK functionality.
      mysql-test/t/flush_read_lock_kill-master.opt:
        We no longer need to use make_global_read_lock_block_commit_loop
        debug tag in this test. Instead we rely on an appropriate
        debug_sync point in MDL code.
      mysql-test/t/flush_read_lock_kill.test:
        Adjusted test case after replacing custom global read lock
        implementation with one based on metadata locks. Use new
        debug_sync point. Do not disable concurrent inserts as now
        InnoDB we always use InnoDB table.
      mysql-test/t/lock_multi.test:
        Adjusted test case after changing thread state names which
        are used when DML or DDL waits for FLUSH TABLES WITH READ
        LOCK to "Waiting for global read lock".
      mysql-test/t/mdl_sync.test:
        Adjusted test case after replacing custom global read lock
        implementation with one based on metadata locks. Replaced
        usage of GRL-specific debug_sync's with appropriate sync
        points in MDL subsystem. Updated thread state names which
        are used when DDL waits for FTWRL.
      mysql-test/t/trigger_notembedded.test:
        Adjusted test case after changing thread state names which
        are used when DML or DDL waits for FLUSH TABLES WITH READ
        LOCK to "Waiting for global read lock".
      sql/event_data_objects.cc:
        Removed Event_queue_element::status/last_executed_changed
        members and Event_queue_element::update_timing_fields()
        method. We no longer use this class for updating mysql.events
        once event is chosen for execution. Accesses to instances of
        this class in scheduler thread require protection by
        Event_queue::LOCK_event_queue mutex and we try to avoid
        updating table while holding this lock.
      sql/event_data_objects.h:
        Removed Event_queue_element::status/last_executed_changed
        members and Event_queue_element::update_timing_fields()
        method. We no longer use this class for updating mysql.events
        once event is chosen for execution. Accesses to instances of
        this class in scheduler thread require protection by
        Event_queue::LOCK_event_queue mutex and we try to avoid
        updating table while holding this lock.
      sql/event_db_repository.cc:
        - Changed Event_db_repository methods to not release all
          metadata locks once they are done updating mysql.events
          table. This allows to keep metadata lock protecting
          against GRL and lock protecting particular event around
          until corresponding DDL statement is written to the binary
          log.
        - Removed logic for conditional update of "status" and
          "last_executed" fields from update_timing_fields_for_event()
          method. In the only case when this method is called now
          "last_executed" is always modified and tracking change
          of "status" is too much hassle.
      sql/event_db_repository.h:
        Removed logic for conditional update of "status" and
        "last_executed" fields from Event_db_repository::
        update_timing_fields_for_event() method.
        In the only case when this method is called now "last_executed"
        is always modified and tracking change of "status" field is
        too much hassle.
      sql/event_queue.cc:
        Changed event scheduler code not to update mysql.events
        table while holding Event_queue::LOCK_event_queue mutex.
        Doing so led to a deadlock with a new GRL implementation.
        This deadlock didn't occur with old implementation due to
        fact that code acquiring protection against GRL ignored
        pending GRL requests (which lead to GRL starvation).
        One of goals of new implementation is to disallow GRL
        starvation and so we have to solve problem with this
        deadlock in a different way.
      sql/events.cc:
        Changed methods of Events class to acquire protection
        against GRL while perfoming DDL statement and keep it
        until statement is written to the binary log.
        Unfortunately this step together with new GRL implementation
        exposed deadlock involving Events::LOCK_event_metadata
        and GRL. To solve it Events::LOCK_event_metadata mutex was
        replaced with a metadata lock on event. As a side-effect
        events DDL has to be prohibited under LOCK TABLES even in
        cases when mysql.events table was explicitly locked for
        write.
      sql/events.h:
        Replaced Events::LOCK_event_metadata mutex with a metadata
        lock on event.
      sql/ha_ndbcluster.cc:
        Updated code after replacing custom global read lock
        implementation with one based on MDL. Since MDL subsystem
        should now be able to detect deadlocks involving metadata
        locks and GRL there is no need for special handling of
        active GRL.
      sql/handler.cc:
        Replaced custom implementation of global read lock with
        one based on metadata locks. Consequently when doing
        commit instead of calling method of Global_read_lock
        class to acquire protection against GRL we simply acquire
        IX in COMMIT namespace.
      sql/lock.cc:
        Replaced custom implementation of global read lock with
        one based on metadata locks. This step allows to expose
        wait for GRL to deadlock detector of MDL subsystem and
        thus succesfully resolve deadlocks similar to one behind
        bug #57006 "Deadlock between HANDLER and FLUSH TABLES
        WITH READ LOCK". It also solves problem with GRL starvation
        described in bug #54673 "It takes too long to get readlock
        for 'FLUSH TABLES WITH READ LOCK'" since metadata locks used
        by GRL give preference to FTWRL statement instead of DML
        statements (if needed in future this can be changed to
        fair scheduling).
        
        Similar to old implementation of acquisition of GRL is
        two-step. During the first step we block all concurrent
        DML and DDL statements by acquiring global S metadata lock
        (each DML and DDL statement acquires global IX lock for
        its duration). During the second step we block commits by
        acquiring global S lock in COMMIT namespace (commit code
        acquires global IX lock in this namespace).
        
        Note that unlike in old implementation acquisition of
        protection against GRL in DML and DDL is semi-automatic.
        We assume that any statement which should be blocked by GRL
        will either open and acquires write-lock on tables or acquires
        metadata locks on objects it is going to modify. For any such
        statement global IX metadata lock is automatically acquired
        for its duration.
        
        To support this change:
        - Global_read_lock::lock/unlock_global_read_lock and
          make_global_read_lock_block_commit methods were changed
          accordingly.
        - Global_read_lock::wait_if_global_read_lock() and
          start_waiting_global_read_lock() methods were dropped.
          It is now responsibility of code acquiring metadata locks
          opening tables to acquire protection against GRL by
          explicitly taking global IX lock with statement duration.
        - Global variables, mutex and condition variable used by
          old implementation was removed.
        - lock_routine_name() was changed to use statement duration for
          its global IX lock. It was also renamed to lock_object_name()
          as it now also used to take metadata locks on events.
        - Global_read_lock::set_explicit_lock_duration() was added which
          allows not to release locks used for GRL when leaving prelocked
          mode.
      sql/lock.h:
        - Renamed lock_routine_name() to lock_object_name() and changed
          its signature to allow its usage for events.
        - Removed broadcast_refresh() function. It is no longer needed
          with new GRL implementation.
      sql/log_event.cc:
        Release metadata locks with statement duration at the end
        of processing legacy event for LOAD DATA. This ensures that
        replication thread processing such event properly releases
        its protection against global read lock.
      sql/mdl.cc:
        Changed MDL subsystem to support new MDL-based implementation
        of global read lock.
        
        Added COMMIT and EVENTS namespaces for metadata locks. Changed
        thread state name for GLOBAL namespace to "Waiting for global
        read lock".
        
        Optimized MDL_map::find_or_insert() method to avoid taking
        m_mutex mutex when looking up MDL_lock objects for GLOBAL
        or COMMIT namespaces. We keep pre-created MDL_lock objects
        for these namespaces around and simply return pointers to
        these global objects when needed.
        
        Changed MDL_lock/MDL_scoped_lock to properly handle
        notification of insert delayed handler threads when FTWRL
        takes global S lock.
        
        Introduced concept of lock duration. In addition to locks with
        transaction duration which work in the way which is similar to
        how locks worked before (i.e. they are released at the end of
        transaction), locks with statement and explicit duration were
        introduced.
        Locks with statement duration are automatically released at the
        end of statement. Locks with explicit duration require explicit
        release and obsolete concept of transactional sentinel.
        
        * Changed MDL_request and MDL_ticket classes to support notion
          of duration.
        * Changed MDL_context to keep locks with different duration in
          different lists. Changed code handling ticket list to take
          this into account.
        * Changed methods responsible for releasing locks to take into
          account duration of tickets. Particularly public
          MDL_context::release_lock() method now only can release
          tickets with explicit duration (there is still internal
          method which allows to specify duration). To release locks
          with statement or transaction duration one have to use
          release_statement/transactional_locks() methods.
        * Concept of savepoint for MDL subsystem now has to take into
          account locks with statement duration. Consequently
          MDL_savepoint class was introduced and methods working with
          savepoints were updated accordingly.
        * Added methods which allow to set duration for one or all
          locks in the context.
      sql/mdl.h:
        Changed MDL subsystem to support new MDL-based implementation
        of global read lock.
        
        Added COMMIT and EVENTS namespaces for metadata locks.
        
        Introduced concept of lock duration. In addition to locks with
        transaction duration which work in the way which is similar to
        how locks worked before (i.e. they are released at the end of
        transaction), locks with statement and explicit duration were
        introduced.
        Locks with statement duration are automatically released at the
        end of statement. Locks with explicit duration require explicit
        release and obsolete concept of transactional sentinel.
        
        * Changed MDL_request and MDL_ticket classes to support notion
          of duration.
        * Changed MDL_context to keep locks with different duration in
          different lists. Changed code handling ticket list to take
          this into account.
        * Changed methods responsible for releasing locks to take into
          account duration of tickets. Particularly public
          MDL_context::release_lock() method now only can release
          tickets with explicit duration (there is still internal
          method which allows to specify duration). To release locks
          with statement or transaction duration one have to use
          release_statement/transactional_locks() methods.
        * Concept of savepoint for MDL subsystem now has to take into
          account locks with statement duration. Consequently
          MDL_savepoint class was introduced and methods working with
          savepoints were updated accordingly.
        * Added methods which allow to set duration for one or all
          locks in the context.
      sql/mysqld.cc:
        Removed global mutex and condition variables which were used
        by old implementation of GRL.
        Also we no longer need to initialize Events::LOCK_event_metadata
        mutex as it was replaced with metadata locks on events.
      sql/mysqld.h:
        Removed global variable, mutex and condition variables which
        were used by old implementation of GRL.
      sql/rpl_rli.cc:
        When slave thread closes tables which were open for handling
        of RBR events ensure that it releases global IX lock which
        was acquired as protection against GRL.
      sql/sp.cc:
        Adjusted code to the new signature of lock_object/routine_name(),
        to the fact that one now needs specify duration of lock when
        initializing MDL_request and to the fact that savepoints for MDL
        subsystem are now represented by MDL_savepoint class.
      sql/sp_head.cc:
        Ensure that statements in stored procedures release statement
        metadata locks and thus release their protectiong against GRL
        in proper moment in time.
        Adjusted code to the fact that one now needs specify duration
        of lock when initializing MDL_request.
      sql/sql_admin.cc:
        Adjusted code to the fact that one now needs specify duration
        of lock when initializing MDL_request.
      sql/sql_base.cc:
        - Implemented support for new approach to acquiring protection
          against global read lock. We no longer acquire such protection
          explicitly on the basis of statement flags. Instead we always
          rely on code which is responsible for acquiring metadata locks
          on object to be changed acquiring this protection. This is
          achieved by acquiring global IX metadata lock with statement
          duration. Code doing this also responsible for checking that
          current connection has no active GRL by calling an
          Global_read_lock::can_acquire_protection() method.
          Changed code in open_table() and lock_table_names()
          accordingly.
          Note that as result of this change DDL and DML on temporary
          tables is always compatible with GRL (before it was
          incompatible in some cases and compatible in other cases).
        - To speed-up code acquiring protection against GRL introduced
          m_has_protection_against_grl member in Open_table_context
          class. It indicates that protection was already acquired
          sometime during open_tables() execution and new attempts
          can be skipped.
        - Thanks to new GRL implementation calls to broadcast_refresh()
          became unnecessary and were removed.
        - Adjusted code to the fact that one now needs specify duration
          of lock when initializing MDL_request and to the fact that
          savepoints for MDL subsystem are now represented by
          MDL_savepoint class.
      sql/sql_base.h:
        Adjusted code to the fact that savepoints for MDL subsystem are
        now represented by MDL_savepoint class.
        Also introduced Open_table_context::m_has_protection_against_grl
        member which allows to avoid acquiring protection against GRL
        while opening tables if such protection was already acquired.
      sql/sql_class.cc:
        Changed THD::leave_locked_tables_mode() after transactional
        sentinel for metadata locks was obsoleted by introduction of
        locks with explicit duration.
      sql/sql_class.h:
        - Adjusted code to the fact that savepoints for MDL subsystem
          are now represented by MDL_savepoint class.
        - Changed Global_read_lock class according to changes in
          global read lock implementation:
          * wait_if_global_read_lock and start_waiting_global_read_lock
            are now gone. Instead code needing protection against GRL
            has to acquire global IX metadata lock with statement
            duration itself. To help it new can_acquire_protection()
            was introduced. Also as result of the above change
            m_protection_count member is gone too.
          * Added m_mdl_blocks_commits_lock member to store metadata
            lock blocking commits.
          * Adjusted code to the fact that concept of transactional
            sentinel was obsoleted by concept of lock duration.
        - Removed CF_PROTECT_AGAINST_GRL flag as it is no longer
          necessary. New GRL implementation acquires protection
          against global read lock automagically when statement
          acquires metadata locks on tables or other objects it
          is going to change.
      sql/sql_db.cc:
        Adjusted code to the fact that one now needs specify duration
        of lock when initializing MDL_request.
      sql/sql_handler.cc:
        Removed call to broadcast_refresh() function. It is no longer
        needed with new GRL implementation.
        Adjusted code after introducing duration concept for metadata
        locks. Particularly to the fact transactional sentinel was
        replaced with explicit duration.
      sql/sql_handler.h:
        Renamed mysql_ha_move_tickets_after_trans_sentinel() to
        mysql_ha_set_explicit_lock_duration() after transactional
        sentinel was obsoleted by locks with explicit duration.
      sql/sql_insert.cc:
        Adjusted code handling delaying inserts after switching to
        new GRL implementation. Now connection thread initiating
        delayed insert has to acquire global IX lock in addition
        to metadata lock on table being inserted into. This IX lock
        protects against GRL and similarly to SW lock on table being
        inserted into has to be passed to handler thread in order to
        avoid deadlocks.
      sql/sql_lex.cc:
        LEX::protect_against_global_read_lock member is no longer
        necessary since protection against GRL is automatically
        taken by code acquiring metadata locks/opening tables.
      sql/sql_lex.h:
        LEX::protect_against_global_read_lock member is no longer
        necessary since protection against GRL is automatically
        taken by code acquiring metadata locks/opening tables.
      sql/sql_parse.cc:
        - Implemented support for new approach to acquiring protection
          against global read lock. We no longer acquire such protection
          explicitly on the basis of statement flags. Instead we always
          rely on code which is responsible for acquiring metadata locks
          on object to be changed acquiring this protection. This is
          achieved by acquiring global IX metadata lock with statement
          duration. This lock is automatically released at the end of
          statement execution.
        - Changed implementation of CREATE/DROP PROCEDURE/FUNCTION not
          to release metadata locks and thus protection against of GRL
          in the middle of statement execution.
        - Adjusted code to the fact that one now needs specify duration
          of lock when initializing MDL_request and to the fact that
          savepoints for MDL subsystem are now represented by
          MDL_savepoint class.
      sql/sql_prepare.cc:
        Adjusted code to the to the fact that savepoints for MDL
        subsystem are now represented by MDL_savepoint class.
      sql/sql_rename.cc:
        With new GRL implementation there is no need to explicitly
        acquire protection against GRL before renaming tables.
        This happens automatically in code which acquires metadata
        locks on tables being renamed.
      sql/sql_show.cc:
        Adjusted code to the fact that one now needs specify duration
        of lock when initializing MDL_request and to the fact that
        savepoints for MDL subsystem are now represented by
        MDL_savepoint class.
      sql/sql_table.cc:
        - With new GRL implementation there is no need to explicitly
          acquire protection against GRL before dropping tables.
          This happens automatically in code which acquires metadata
          locks on tables being dropped.
        - Changed mysql_alter_table() not to release lock on new table
          name explicitly and to rely on automatic release of locks
          at the end of statement instead. This was necessary since
          now MDL_context::release_lock() is supported only for locks
          for explicit duration.
      sql/sql_trigger.cc:
        With new GRL implementation there is no need to explicitly
        acquire protection against GRL before changing table triggers.
        This happens automatically in code which acquires metadata
        locks on tables which triggers are to be changed.
      sql/sql_update.cc:
        Fix bug exposed by GRL testing. During prepare phase acquire
        only S metadata locks instead of SW locks to keep prepare of
        multi-UPDATE compatible with concurrent LOCK TABLES WRITE
        and global read lock.
      sql/sql_view.cc:
        With new GRL implementation there is no need to explicitly
        acquire protection against GRL before creating view.
        This happens automatically in code which acquires metadata
        lock on view to be created.
      sql/sql_yacc.yy:
        LEX::protect_against_global_read_lock member is no longer
        necessary since protection against GRL is automatically
        taken by code acquiring metadata locks/opening tables.
      sql/table.cc:
        Adjusted code to the fact that one now needs specify duration
        of lock when initializing MDL_request.
      sql/table.h:
        Adjusted code to the fact that one now needs specify duration
        of lock when initializing MDL_request.
      sql/transaction.cc:
        Replaced custom implementation of global read lock with
        one based on metadata locks. Consequently when doing
        commit instead of calling method of Global_read_lock
        class to acquire protection against GRL we simply acquire
        IX in COMMIT namespace.
        Also adjusted code to the fact that MDL savepoint is now
        represented by MDL_savepoint class.
      730c3cdc
  3. 03 Nov, 2010 1 commit
    • Marc Alff's avatar
      Bug#57609 performance_schema does not work with lower_case_table_names · db9aeb42
      Marc Alff authored
      Before this fix, the performance schema tables were defined in UPPERCASE.
      
      This was incompatible with the lowercase_table_names option, and caused
      issues with the install / upgrade process, when changing the lower case
      table names setting *after* the install or upgrade.
      
      With this fix, all performance schema tables are exposed with lowercase names.
      As a result, the name of the performance schema table is always lowercase,
      no matter how / if / when the lowercase_table_names setting if changed.
      db9aeb42
  4. 17 Sep, 2010 1 commit
    • Marc Alff's avatar
      Bug#56832 perfschema.server_init test output not consistent · bffb4c1f
      Marc Alff authored
      Before this fix, the test output for perfschema.server_init would
      vary between executions, because some of the objects tested were
      not guaranteed to exist in all configurations / code paths.
      
      This fix removes these weak tests.
      
      Also, comments referring to abandonned code have been cleaned up.
      bffb4c1f
  5. 27 Jul, 2010 1 commit
    • Dmitry Lenev's avatar
      Fix for bug #52044 "FLUSH TABLES WITH READ LOCK and FLUSH · 5bb44ae0
      Dmitry Lenev authored
      TABLES <list> WITH READ LOCK are incompatible".
      
      The problem was that FLUSH TABLES <list> WITH READ LOCK
      which was issued when other connection has acquired global
      read lock using FLUSH TABLES WITH READ LOCK was blocked
      and has to wait until global read lock is released.
      
      This issue stemmed from the fact that FLUSH TABLES <list>
      WITH READ LOCK implementation has acquired X metadata locks
      on tables to be flushed. Since these locks required acquiring
      of global IX lock this statement was incompatible with global
      read lock.
      
      This patch addresses problem by using SNW metadata type of
      lock for tables to be flushed by FLUSH TABLES <list> WITH
      READ LOCK. It is OK to acquire them without global IX lock
      as long as we won't try to upgrade those locks. Since SNW
      locks allow concurrent statements using same table FLUSH
      TABLE <list> WITH READ LOCK now has to wait until old
      versions of tables to be flushed go away after acquiring
      metadata locks. Since such waiting can lead to deadlock
      MDL deadlock detector was extended to take into account
      waits for flush and resolve such deadlocks.
      
      As a bonus code in open_tables() which was responsible for
      waiting old versions of tables to go away was refactored.
      Now when we encounter old version of table in open_table()
      we don't back-off and wait for all old version to go away,
      but instead wait for this particular table to be flushed.
      Such approach supported by deadlock detection should reduce
      number of scenarios in which FLUSH TABLES aborts concurrent
      multi-statement transactions.
      
      Note that active FLUSH TABLES <list> WITH READ LOCK still
      blocks concurrent FLUSH TABLES WITH READ LOCK statement
      as the former keeps tables open and thus prevents the
      latter statement from doing flush.
      
      mysql-test/include/handler.inc:
        Adjusted test case after changing status which is set
        when FLUSH TABLES waits for tables to be flushed from
        "Flushing tables" to "Waiting for table".
      mysql-test/r/flush.result:
        Added test which checks that "flush tables <list> with
        read lock" is compatible with active "flush tables with
        read lock" but not vice-versa. This test also covers
        bug #52044 "FLUSH TABLES WITH READ LOCK and FLUSH TABLES
        <list> WITH READ LOCK are incompatible".
      mysql-test/r/mdl_sync.result:
        Added scenarios in which wait for table to be flushed
        causes deadlocks to the coverage of MDL deadlock detector.
      mysql-test/suite/perfschema/r/dml_setup_instruments.result:
        Adjusted test results after removal of COND_refresh
        condition variable.
      mysql-test/suite/perfschema/r/server_init.result:
        Adjusted test and its results after removal of COND_refresh
        condition variable.
      mysql-test/suite/perfschema/t/server_init.test:
        Adjusted test and its results after removal of COND_refresh
        condition variable.
      mysql-test/t/flush.test:
        Added test which checks that "flush tables <list> with
        read lock" is compatible with active "flush tables with
        read lock" but not vice-versa. This test also covers
        bug #52044 "FLUSH TABLES WITH READ LOCK and FLUSH TABLES
        <list> WITH READ LOCK are incompatible".
      mysql-test/t/kill.test:
        Adjusted test case after changing status which is set
        when FLUSH TABLES waits for tables to be flushed from
        "Flushing tables" to "Waiting for table".
      mysql-test/t/lock_multi.test:
        Adjusted test case after changing status which is set
        when FLUSH TABLES waits for tables to be flushed from
        "Flushing tables" to "Waiting for table".
      mysql-test/t/mdl_sync.test:
        Added scenarios in which wait for table to be flushed
        causes deadlocks to the coverage of MDL deadlock detector.
      sql/ha_ndbcluster.cc:
        Adjusted code after adding one more parameter for
        close_cached_tables() call - timeout for waiting for
        table to be flushed.
      sql/ha_ndbcluster_binlog.cc:
        Adjusted code after adding one more parameter for
        close_cached_tables() call - timeout for waiting for
        table to be flushed.
      sql/lock.cc:
        Removed COND_refresh condition variable. See comment
        for sql_base.cc for details.
      sql/mdl.cc:
        Now MDL deadlock detector takes into account information
        about waits for table flushes when searching for deadlock.
        To implement this change:
        - Declaration of enum_deadlock_weight and
          Deadlock_detection_visitor were moved to mdl.h header
          to make them available to the code in table.cc which
          implements deadlock detector traversal through edges
          of waiters graph representing waiting for flush.
        - Since now MDL_context may wait not only for metadata
          lock but also for table to be flushed an abstract
          Wait_for_edge class was introduced. Its descendants
          MDL_ticket and Flush_ticket incapsulate specifics
          of inspecting waiters graph when following through
          edge representing wait of particular type.
        
        We no longer require global IX metadata lock when acquiring
        SNW or SNRW locks. Such locks are needed only when metadata
        locks of these types are upgraded to X locks. This allows
        to use SNW locks in FLUSH TABLES <list> WITH READ LOCK
        implementation and keep the latter compatible with global
        read lock.
      sql/mdl.h:
        Now MDL deadlock detector takes into account information
        about waits for table flushes when searching for deadlock.
        To implement this change:
        - Declaration of enum_deadlock_weight and
          Deadlock_detection_visitor were moved to mdl.h header
          to make them available to the code in table.cc which
          implements deadlock detector traversal through edges
          of waiters graph representing waiting for flush.
        - Since now MDL_context may wait not only for metadata
          lock but also for table to be flushed an abstract
          Wait_for_edge class was introduced. Its descendants
          MDL_ticket and Flush_ticket incapsulate specifics
          of inspecting waiters graph when following through
          edge representing wait of particular type.
        - Deadlock_detection_visitor now has m_table_shares_visited
          member which allows to support recursive locking for
          LOCK_open. This is required when deadlock detector
          inspects waiters graph which contains several edges
          representing waits for flushes or needs to come through
          the such edge more than once.
      sql/mysqld.cc:
        Removed COND_refresh condition variable. See comment
        for sql_base.cc for details.
      sql/mysqld.h:
        Removed COND_refresh condition variable. See comment
        for sql_base.cc for details.
      sql/sql_base.cc:
        Changed approach to how threads are waiting for table
        to be flushed. Now thread that wants to wait for old
        table to go away subscribes for notification by adding
        Flush_ticket to table's share and waits using
        MDL_context::m_wait object. Once table gets flushed
        (i.e. all tables are closed and table share is ready
        to be destroyed) all such waiters are notified
        individually.
        Thanks to this change MDL deadlock detector can take
        such waits into account.
        
        To implement this/as result of this change:
        - tdc_wait_for_old_versions() was replaced with
          tdc_wait_for_old_version() which waits for individual
          old share to go away and which is called by open_table()
          after finding out that share is outdated. We don't
          need to perform back-off before such waiting thanks
          to the fact that deadlock detector now sees such waits.
        - As result Open_table_ctx::m_mdl_requests became
          unnecessary and was removed. We no longer allocate
          copies of MDL_request objects on MEM_ROOT when
          MYSQL_OPEN_FORCE_SHARED/SHARED_HIGH_PRIO flags are
          in effect.
        - close_cached_tables() and tdc_wait_for_old_version()
          share code which implements waiting for share to be
          flushed - the both use TABLE_SHARE::wait_until_flush()
          method. Thanks to this close_cached_tables() supports
          timeouts and has extra parameter for this.
        - Open_table_context::OT_MDL_CONFLICT enum element was
          renamed to OT_CONFLICT as it is now also used in cases
          when back-off is required to resolve deadlock caused
          by waiting for flush and not metadata lock.
        - In cases when we discover that current connection tries
          to open tables from different generation we now simply
          back-off and restart process of opening tables. To
          support this Open_table_context::OT_REOPEN_TABLES enum
          element was added.
        - COND_refresh condition variable became unnecessary and
          was removed.
        - mysql_notify_thread_having_shared_lock() no longer wakes
          up connections waiting for flush as all such connections
          can be waken up by deadlock detector if necessary.
      sql/sql_base.h:
        - close_cached_tables() now has one more parameter -
          timeout for waiting for table to be flushed.
        - Open_table_context::OT_MDL_CONFLICT enum element was
          renamed to OT_CONFLICT as it is now also used in cases
          when back-off is required to resolve deadlock caused
          by waiting for flush and not metadata lock.
          Added new OT_REOPEN_TABLES enum element to be used in
          cases when we need to restart open tables process even
          in the middle of transaction.
        - Open_table_ctx::m_mdl_requests became unnecessary and
          was removed.
      sql/sql_class.h:
        Added assert ensuring that we won't use LOCK_open mutex
        with THD::enter_cond(). Otherwise deadlocks can arise in
        MDL deadlock detector.
      sql/sql_parse.cc:
        Changed FLUSH TABLES <list> WITH READ LOCK to take SNW
        metadata locks instead of X locks on tables to be flushed.
        Since we no longer require global IX lock to be taken
        when SNW locks are taken this makes this statement
        compatible with FLUSH TABLES WITH READ LOCK statement.
        Since SNW locks allow other connections to have table
        opened FLUSH TABLES <list> WITH READ LOCK now has to
        wait during open_tables() for old version to go away.
        Such waits can lead to deadlocks which will be detected
        by MDL deadlock detector which now takes waits for table
        to be flushed into account.
        
        Also adjusted code after adding one more parameter for
        close_cached_tables() call - timeout for waiting for
        table to be flushed.
      sql/sql_yacc.yy:
        FLUSH TABLES <list> WITH READ LOCK now needs only SNW
        metadata locks on tables.
      sql/sys_vars.cc:
        Adjusted code after adding one more parameter for
        close_cached_tables() call - timeout for waiting for
        table to be flushed.
      sql/table.cc:
        Implemented new approach to how threads are waiting for
        table to be flushed. Now thread that wants to wait for
        old table to go away subscribes for notification by
        adding Flush_ticket to table's share and waits using
        MDL_context::m_wait object. Once table gets flushed
        (i.e. all tables are closed and table share is ready
        to be destroyed) all such waiters are notified
        individually. This change allows to make such waits
        visible inside of MDL deadlock detector.
        To do it:
        
        - Added list of waiters/Flush_tickets to TABLE_SHARE
          class.
        - Changed free_table_share() to postpone freeing of
          share memory until last waiter goes away and to
          wake up subscribed waiters.
        - Added TABLE_SHARE::wait_until_flushed() method which
          implements subscription to the list of waiters for
          table to be flushed and waiting for this event.
        
        Implemented interface which allows to expose waits for
        flushes to MDL deadlock detector:
        
        - Introduced Flush_ticket class a descendant of
          Wait_for_edge class.
        - Added TABLE_SHARE::find_deadlock() method which allows
          deadlock detector to find out what contexts are still
          using old version of table in question (i.e. to find
          out what contexts are waited for by owner of
          Flush_ticket).
      sql/table.h:
        In order to support new strategy of waiting for table flush
        (see comment for table.cc for details) added list of
        waiters/Flush_tickets to TABLE_SHARE class.
        
        Implemented interface which allows to expose waits for
        flushes to MDL deadlock detector:
        - Introduced Flush_ticket class a descendant of
          Wait_for_edge class.
        - Added TABLE_SHARE::find_deadlock() method which allows
          deadlock detector to find out what contexts are still
          using old version of table in question (i.e. to find
          out what contexts are waited for by owner of
          Flush_ticket).
      5bb44ae0
  6. 23 Jul, 2010 1 commit
  7. 01 Jul, 2010 1 commit
    • Jon Olav Hauglid's avatar
      A 5.5 version of the fix for Bug #54360 "Deadlock DROP/ALTER/CREATE · f646c889
      Jon Olav Hauglid authored
      DATABASE with open HANDLER"
      
      Remove LOCK_create_db, database name locks, and use metadata locks instead.
      This exposes CREATE/DROP/ALTER DATABASE statements to the graph-based
      deadlock detector in MDL, and paves the way for a safe, deadlock-free
      implementation of RENAME DATABASE.
      
      Database DDL statements will now take exclusive metadata locks on
      the database name, while table/view/routine DDL statements take
      intention exclusive locks on the database name. This prevents race
      conditions between database DDL and table/view/routine DDL.
      (e.g. DROP DATABASE with concurrent CREATE/ALTER/DROP TABLE)
      
      By adding database name locks, this patch implements
      WL#4450 "DDL locking: CREATE/DROP DATABASE must use database locks" and
      WL#4985 "DDL locking: namespace/hierarchical locks".
      
      The patch also changes code to use init_one_table() where appropriate.
      The new lock_table_names() function requires TABLE_LIST::db_length to
      be set correctly, and this is taken care of by init_one_table().
      
      This patch also adds a simple template to help work with 
      the mysys HASH data structure.
      
      Most of the patch was written by Konstantin Osipov.
      f646c889
  8. 12 Jan, 2010 1 commit