BOGUS "THE TABLE MYSQL.PROC IS MISSING,..."
There was a race condition between loading a stored routine
(function/procedure/trigger) specified by fully qualified name
SCHEMA_NAME.PROC_NAME and dropping the stored routine database.
The problem was that there is a window for race condition when one server
thread tries to load a stored routine being executed and the other thread
tries to drop the stored routine schema.
This condition race window exists in implementation of function
mysql_change_db() called by db_load_routine() during loading of stored
routine to cache. Function mysql_change_db() calls check_db_dir_existence()
that might failed because specified database was dropped during concurrent
execution of DROP SCHEMA statement. db_load_routine() calls mysql_change_db()
with flag 'force_switch' set to 'true' value so when referenced db is not found
then my_error() is not called and function mysql_change_db() returns ok.
This shadows information about schema opening error in db_load_routine().
Then db_load_routine() makes attempt to parse stored routine that is failed.
This makes to return error to sp_cache_routines_and_add_tables_aux() but since
during error generation a call to my_error wasn't made and hence
THD::main_da wasn't set we set the generic "mysql.proc table corrupt" error
when running sp_cache_routines_and_add_tables_aux().
The fix is to install an error handler inside db_load_routine() for
the mysql_op_change_db() call, and check later if the ER_BAD_DB_ERROR
was caught.
locks for DML statements and changes the way MDL locks
are acquired/granted in contended case.
Instead of backing-off when a lock conflict is encountered
and waiting for it to go away before restarting open_tables()
process we now wait for lock to be released without releasing
any previously acquired locks. If conflicting lock goes away
we resume opening tables. If waiting leads to a deadlock we
try to resolve it by backing-off and restarting open_tables()
immediately.
As result both waiting for possibility to acquire and
acquiring of a metadata lock now always happen within the
same MDL API call. This has allowed to make release of a lock
and granting it to the most appropriate pending request an
atomic operation.
Thanks to this it became possible to wake up during release
of lock only those waiters which requests can be satisfied
at the moment as well as wake up only one waiter in case
when granting its request would prevent all other requests
from being satisfied. This solves thundering herd problem
which occured in cases when we were releasing some lock and
woke up many waiters for SNRW or X locks (this was the issue
in bug#52289 "performance regression for MyISAM in sysbench
OLTP_RW test".
This also allowed to implement more fair (FIFO) scheduling
among waiters with the same priority.
It also opens the door for introducing new types of requests
for metadata locks such as low-prio SNRW lock which is
necessary in order to support LOCK TABLES LOW_PRIORITY WRITE.
Notice that after this sometimes can report ER_LOCK_DEADLOCK
error in cases in which it has not happened before.
Particularly we will always report this error if waiting for
conflicting lock has happened in the middle of transaction
and resulted in a deadlock. Before this patch the error was
not reported if deadlock could have been resolved by backing
off all metadata locks acquired by the current statement.
MySQL handles the join syntax "JOIN ... USING( field1,
... )" and natural joins by building the same parse tree as
a corresponding join with an "ON t1.field1 = t2.field1 ..."
expression would produce. This parse tree was not cleaned up
properly in the following scenario. If a thread tries to
lock some tables and finds that the tables were dropped and
re-created while waiting for the lock, it cleans up column
references in the statement by means a per-statement free
list. But if the statement was part of a stored procedure,
column references on the stored procedure's free list weren't
cleaned up and thus contained pointers to freed objects.
Fixed by adding a call to clean up the current prepared
statement's free list.
