Commit 76d2846a71 was for 10.5 only.
It caused some performance regression on 10.6 in some cases,
likely related to the removal of ib_mutex_t in MDEV-21452.
As pointed out by Andrei Elkin, the previous fix did not fix one
race condition that may have caused the observed hang.
innodb_log_flush_request(): If we are enqueueing the very first
request at the same time the log write is being completed,
we must ensure that a near-concurrent call to log_flush_notify()
will not result in a missed notification. We guarantee this by
release-acquire operations on log_requests.start and
log_sys.flushed_to_disk_lsn.
log_flush_notify_and_unlock(): Cleanup: Always release the mutex.
log_sys_t::get_flushed_lsn(): Use acquire memory order.
log_sys_t::set_flushed_lsn(): Use release memory order.
log_sys_t::set_lsn(): Use release memory order.
log_sys_t::get_lsn(): Use relaxed memory order by default, and
allow the caller to specify acquire memory order explicitly.
Whenever the log_sys.mutex is being held or when log writes are
prohibited during startup, we can use a relaxed load. Likewise,
in some assertions where reading a stale value of log_sys.lsn
should not matter, we can use a relaxed load.
This will cause some additional instructions to be emitted on
architectures that do not implement Total Store Ordering (TSO),
such as POWER, ARM, and RISC-V Weak Memory Ordering (RVWMO).
track page-access counter
As part of MDEV-21212, n_page_gets that is meant to track page access,
is ported to use distributed counter that default uses atomic sub-counters.
n_page_gets originally was a non-atomic counter that represented an approximate
value of pages tracked. Using the said analogy it doesn't need to be
an atomic distributed counter.
This patch introduces an interface that allows distributed counter to be
used with atomic and non-atomic sub-counter (through template) and also
port n_page_gets to use non-atomic distributed counter using the said
updated interface.
Atomic_relaxed<T>: add fetch_or() and fetch_and()
innodb_init(): rely on a zero-initialization of a global variable
monitor_set_tbl: make Atomic_relaxed<ulint> array and use proper operations
for setting bit, unsetting bit and reading bit
Reviewed by: Marko Mäkelä
