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.
Detailed revision comments:
r6749 | vasil | 2010-02-20 18:45:41 +0200 (Sat, 20 Feb 2010) | 5 lines
Non-functional change: update copyright year to 2010 of the files
that have been modified after 2010-01-01 according to svn.
for f in $(svn log -v -r{2010-01-01}:HEAD |grep "^ M " |cut -b 16- |sort -u) ; do sed -i "" -E 's/(Copyright \(c\) [0-9]{4},) [0-9]{4}, (.*Innobase Oy.+All Rights Reserved)/\1 2010, \2/' $f ; done
Detailed revision comments:
r6449 | marko | 2010-01-13 22:38:53 +0200 (Wed, 13 Jan 2010) | 18 lines
branches/zip: lock_rec_validate_page(): Only validate the record
queues when the thread is not holding a space->latch.
When UNIV_DEBUG is defined while UNIV_SYNC_DEBUG is not,
latching order violations will still occur and deadlocks will be possible.
sync_thread_levels_nonempty_gen(): Renamed from
sync_thread_levels_empty_gen(). Return the violating latch or NULL
instead of FALSE or TRUE, except that there will be a ut_error before
the non-NULL return.
sync_thread_levels_empty_gen(): A macro that negates the return value of
sync_thread_levels_nonempty_gen().
sync_thread_levels_contains(): New function, based on
sync_thread_levels_nonempty_gen().
This should fix Issue #441.
