------------------------------------------------------------
  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.