• Sunny Bains's avatar
    Fix bug#54583. This change reverses rsvn:1350 by getting rid of a bogus assertion · 72998587
    Sunny Bains authored
    and clarifies the invariant in dict_table_get_on_id().
          
    In Mar 2007 Marko observed a crash during recovery, the crash resulted from
    an UNDO operation on a system table. His solution was to acquire an X lock on
    the data dictionary, this in hindsight was an overkill. It is unclear what
    caused the crash, current hypothesis is that it was a memory corruption.
          
    The X lock results in performance issues by when undoing changes due to
    rollback during normal operation on regular tables.
          
    Why the change is safe:
    ======================
    The InnoDB code has changed since the original X lock change was made. In the
    new code we always lock the data dictionary in X mode during startup when
    UNDOing operations on the system tables (this is a given). This ensures that
    the crash Marko observed cannot happen as long as all transactions that update
    the system tables follow the standard rules by setting the appropriate DICT_OP
    flag when writing the log records when they make the changes.
          
    If transactions violate the above mentioned rule then during recovery (at
    startup) the rollback code (see trx0roll.c) will not acquire the X lock
    and we will see the crash again.  This will however be a different bug.
    72998587
sync0sync.h 18.1 KB