partition by system_time (
    partition p0 history,
    partition pn current
 )

non-standard, redundant, potentially risky in the future,
hides bugs. See #383, #384, #385

Fixed a parser bug where
SELECT * FROM (t1 join t2) FOR SYSTEM_TIME ...
was not an error.

they store history and the history does not have history

Merge branch '10.3' into trunk

    commit 6d63a034
    MDEV-11297: Add support for LIMIT clause in GROUP_CONCAT()

  * Note: breaking change; since this commit, a plugin that has
    worked so far might get rejected due to plugin maturity
  * mariabackup is not affected (allows all plugins)
  * VERSION file defines SERVER_MATURITY, which defines the
    corresponding numeric value as SERVER_MATURITY_LEVEL in
    include/mysql_version.h
  * The default value for 'plugin_maturity' is SERVER_MATURITY_LEVEL - 1
  * Logs a warning if a plugin has maturity lower than
    SERVER_MATURITY_LEVEL
  * Tests suppress the plugin maturity warning
  * Tests use --plugin-maturity=unknown by default so as not to fail
    due to the stricter plugin maturity handling

Renamed to SELECT_LEX::vers_setup_conds().
Moved optimized fields check to JOIN::vers_check_items().

Relax memory barrier for lock_word.

rw_lock_lock_word_decr() - used to acquire rw-lock, thus we only need to issue
ACQUIRE when we succeed locking.

rw_lock_x_lock_func_nowait() - same as above, but used to attempt to acquire
X-lock.

rw_lock_s_unlock_func() - used to release S-lock, RELEASE is what we need here.

rw_lock_x_unlock_func() - used to release X-lock. Ideally we'd need only RELEASE
here, but due to mess with waiters (they must be loaded after lock_word is
stored) we have to issue both ACQUIRE and RELEASE.

rw_lock_sx_unlock_func() - same as above, but used to release SX-lock.

rw_lock_s_lock_spin(), rw_lock_x_lock_func(), rw_lock_sx_lock_func() -
fetch-and-store to waiters has to issue only ACQUIRE memory barrier, so that
waiters are stored before lock_word is loaded.

Note that there is violation of RELEASE-ACQUIRE protocol here, because we do
on lock:

  my_atomic_fas32_explicit((int32*) &lock->waiters, 1, MY_MEMORY_ORDER_ACQUIRE);
  my_atomic_load32_explicit(&lock->lock_word, MY_MEMORY_ORDER_RELAXED);

on unlock

  my_atomic_add32_explicit(&lock->lock_word, X_LOCK_DECR, MY_MEMORY_ORDER_ACQ_REL);
  my_atomic_load32_explicit((int32*) &lock->waiters, MY_MEMORY_ORDER_RELAXED);

That is we kind of synchronize ACQUIRE on lock_word with ACQUIRE on waiters.
It was there before this patch. Simple fix may have negative performance impact.
Proper fix requires refactoring of lock_word.

Relax memory barrier for waiters: these 2 stores must be completed before
os_event_set() finishes. This is guaranteed by RELEASE barrier issued by
mutex.exit() of os_event_set().

Remove volatile modifier from waiters: it's not supposed for inter-thread
communication, use appropriate atomic operations instead.

Changed waiters to int32_t, my_atomic friendly type.

Remove volatile modifier from lock_word: it's not supposed for inter-thread
communication, use appropriate atomic operations instead.

Change lock_word from lint to int32_t: the latter is my_atomic_* friendly type.

Related to #365 bug 3.

Tests affected (forced mode):

main.range main.range_mrr_icp

Related to VIEW fix #4 (8e12edbcc74685175d20729958c5f6a5d09e4f9c)

because the statement is TRUNCATE, not DELETE

* again, as in 10.2, NOW is a keyword only if followed by parentheses
* use AS OF CURRENT_TIMESTAMP or AS OF NOW()
* AS OF CURRENT_TIMESTAMP and AS OF NOW() mean AS OF NOW(6),
  not AS OF NOW(0), (same behavior as in a DEFAULT clause)

This is where Codership's offical rpm's puts them

- Remove not used thd_rpl_is_parallel()
- Remove not used mysql_notify_thread_having_shared_lock()
- Remove not needed LOCK_thread_count from MYSQL_BIN_LOG::reset_logs()
  - LOCK_thread_count is not protecting against rollback, so this
    code and comment is not needed
- Remove mutex_locks in slave.cc that are not needed.
  Added THD::assert_not_linked() to ensure that it was safe to remove
- Fixed not repeatable test load_data_stmt_view
- Updated binlog_killed to test removal of mutex
  (thanks to Andrei Elkin for test)
- More code comments

When logging ROW_T_INSERT or ROW_T_UPDATE records, we did not normalize
the DB_TRX_ID of the current transaction into 0 if the current transaction
had started (modifying other tables) before the ALTER TABLE started.

MDEV-13654 introduced this normalization for ROW_T_DELETE
and for all operations with ADD PRIMARY KEY, in row_log_table_get_pk().

dict_stats_process_entry_from_defrag_pool(): Release the mutex

Follow-up fix to MDEV-13201 Assertion `srv_undo_sources || ...` failed on shutdown during DDL operation

Introduce the debug flag trx_t::persistent_stats to suppress the
assertion for the updates of persistent statistics during fast
shutdown.

dict_stats_exec_sql(): Do execute the statement even though shutdown
has been initiated.