MDEV-30007 SIGSEGV in st_select_lex_unit::is_derived_eliminated, runtime error: member access within null pointer of type 'struct TABLE' in st_select_lex_unit::is_derived_eliminated()

Take into account case of a degenerate subquery (like SELECT 1).

followup for 57d233e2

Make sure that EXPLAIN object allocated on runtime arena.

MDEV-29924 Assertion `(((nr) % (1LL << 24)) % (int) log_10_int[6 - dec]) == 0' failed in my_time_packed_to_binary on SELECT when using TIME field

when assigning the cached item to the Item_cache for the first time
make sure to use Item_cache::setup(), not Item_cache::store().
Because the former copies the metadata (and allocates memory, in case
of Item_cache_row), and Item_cache::decimal must be set for
comparisons to work correctly.

Revert "MDEV-27233 Server hangs when using --init-file which loads Spider and creates a Spider table"

This reverts commit c160a115.

also call top_level_transform() recursively for

(a OR b) AND (c OR d)

it's incorrect to use change_item_tree() to replace arguments
of top-level AND/OR, because they (arguments) are stored in a List,
so a pointer to an argument is in the list_node, and individual
list_node's of top-level AND/OR can be deleted in Item_cond::build_equal_items().
In that case rollback_item_tree_changes() will modify the deleted object.

Luckily, it's not needed to use change_item_tree() for top-level
AND/OR, because the whole top-level item is copied and preserved
in prep_where and prep_on, and restored from there.

So, just don't.

Post-push fix. The flag of transaction which indicates that it's necessary
to forbid gap lock inheritance after XA PREPARE could be inverted if
lock_release_on_prepare_try() is invoked several times. The fix is to
toggle it on lock_release_on_prepare() exit.

The test fails extremely often on a Windows builder, and nobody seems
to be interested in fixing it.

ha_innobase::check(): Do not enable READ UNCOMMITTED isolation level
for temporary tables, because it would report index count mismatch
for secondary indexes.

row_check_index(): Ignore EXTENDED for temporary tables, because
the tables are private to the current connection and there will be
no purge of committed transaction history.

The test innodb.innodb-wl5522-debug would occasionally hang
(especially when run with ./mtr --rr) due to a deadlock between
btr_store_big_rec_extern_fields() and dict_stats_analyze_index().
The two threads would acquire the clustered index root page latch and
the tablespace latch in the opposite order. The deadlock was possible
because dict_stats_analyze_index() was holding the index latch in
shared mode and an index root page latch, while waiting for the
tablespace latch. If a stronger dict_index_t::lock had been held
by dict_stats_analyze_index(), any operations that free or allocate
index pages would have been blocked.

In each caller of fseg_n_reserved_pages() except ibuf_init_at_db_start()
which is a special case for ibuf.index at database startup, we must hold
an index latch that prevents concurrent allocation or freeing of index
pages.

Any operation that allocates or free pages that belong to an index tree
must first acquire an index latch in Update or Exclusive mode, and while
holding that, acquire an index root page latch in Update or Exclusive
mode.

dict_index_t::clear(): Also acquire an index latch. Otherwise,
the test innodb.insert_into_empty could hang.

btr_get_size_and_reserved(): Assert that a strong enough index latch
is being held. Only acquire a shared fil_space_t::latch; we are only
reading, not modifying any data.

dict_stats_update_transient_for_index(),
dict_stats_analyze_index(): Acquire a strong enough index latch. Only
acquire a shared fil_space_t::latch.

These operations had followed the same order of acquiring latches in
every InnoDB version since the very beginning
(commit c533308a).
The calls for acquiring tablespace latch had previously been moved in
commit 87839258 and
commit 1e9c922f.

The hang was introduced in
commit 2e814d47 which imported
mysql/mysql-server@ac74632293bea967b352d1b472abedeeaa921b98
which failed to strengthen the locking requirements of the function
btr_get_size().

1. The merge aeccbbd9 has overwritten
lock0lock.cc, and the changes of MDEV-29622 and MDEV-29635 were
partially lost, this commit restores the changes.

2. innodb.deadlock_wait_thr_race test:

The following hang was found during testing.

There is deadlock_report_before_lock_releasing sync point in
Deadlock::report(), which is waiting for sel_cont signal under lock_sys_t
lock. The signal must be issued after "UPDATE t SET b = 100" rollback,
and that rollback is executing undo record, which is blocked
on dict_sys latch request. dict_sys is locked by the thread of statistics
update(dict_stats_save()), and during that update lock_sys lock is
requested, and can't be acquired as Deadlock::report() holds it. We have
to disable statistics update to make the test stable.

But even if statistics update is disabled, and transaction with consistent
snapshot is started at the very beginning of the test to prevent purging,
the purge can still be invoked for system tables, and it tries to open
system table by id, what causes dict_sys.freeze() call and dict_sys
latching. What, in combination with lock_sys::xx_lock() causes the same
deadlock as described above. We need to disable purging globally for the
test as well.

All the above is applicable to innodb.deadlock_wait_lock_race test also.

Fix a couple of build warnings that fire with CONNECT engine.

MDEV-28822 Table from older version requires table rebuild when adding column to table with multi-column index

This problem was earlier fixed in 10.4 by the patch for MDEV-29481.

Adding MTR tests only.