MDEV-29678 Valgrind/MSAN uninitialised value errors upon PS with ALTER under ONLY_FULL_GROUP_BY
st_select_lex::init_query is called in the exectuion of EXECUTE
IMMEDIATE 'alter table ...'. so reset the initialization at the
same point we set join= 0.
MDEV-27943 Reduce overhead of attaching THD to OS thread, in threadpool
Avoid relatively expensive THD::store_globals() for every query in the
threadpool. Use a lighter version instead, that only resets some thread
local storage variables(THD, mysys, PSI), avoids some calculationms
and caches syscall gettid (Linux only) in a thread_local variable.
after 6b685ea7b077 one can no longer violate the locking protocol
by invoking thd_get_ha_data() on some other thread without
protecting that with a mutex
MDEV-22718: purge_sys.low_limit_no() is not protected
purge_sys_t::low_limit_no(): Adjust a comment. Actually, this
is protected after all.
TrxUndoRsegsIterator::set_next(): Reduce the critical section
of purge_sys.rseg->latch. Some purge_sys fields are accessed
only by the purge coordinator task.
MDEV-29612 ReadViewBase::snapshot() misses an optimization
ReadViewBase::snapshot(): In case m_low_limit_no==m_low_limit_id
and m_ids would include everything between that and m_up_limit_id,
set all fields to m_up_limit_id and clear m_ids, to speed up
changes_visible() and append().
rw_trx_hash_t::debug_iterator(): Add an assertion.
MDEV-29590 Deadlock between ibuf_insert_to_index_page_low() and DDL
btr_page_reorganize_low(): Do not invoke lock_move_reorganize_page()
on a dummy index during change buffer merge. The ibuf.index page
latch that we are holding may block a DDL operation that is waiting
in ibuf_delete_for_discarded_space() while holding exclusive
lock_sys.latch. ibuf_insert_low() would refuse to buffer a change
if any locks exist for the index page.
