The parameter innodb_log_spin_wait_delay will be deprecated and
ignored, because there is no spin loop anymore.
Thanks to commit 685d958e38
and commit a635c40648
multiple mtr_t::commit() can concurrently copy their slice of
mtr_t::m_log to the shared log_sys.buf. Each writer would allocate
their own log sequence number by invoking log_t::append_prepare()
while holding a shared log_sys.latch. This function was too heavy,
because it would invoke a minimum of 4 atomic read-modify-write
operations as well as system calls in the supposedly fast code path.
It turns out that with a simpler data structure, instead of having
several data fields that needed to be kept consistent with each other,
we only need one Atomic_relaxed<uint64_t> write_lsn_offset, on which
we can operate using fetch_add(), fetch_sub() as well as a single-bit
fetch_or(), which reasonably modern compilers (GCC 7, Clang 15 or later)
can translate into loop-free code on AMD64.
Before anything can be written to the log, log_sys.clear_mmap()
must be invoked.
log_t::base_lsn: The LSN of the last write_buf() or persist().
This is a rough approximation of log_sys.lsn, which will be removed.
log_t::write_lsn_offset: An Atomic_relaxed<uint64_t> that buffers
updates of write_to_buf and base_lsn.
log_t::buf_free, log_t::max_buf_free, log_t::lsn. Remove.
Replaced by base_lsn and write_lsn_offset.
log_t::buf_size: Always reflects the usable size in append_prepare().
log_t::lsn_lock: Remove. For the memory-mapped log in resize_write(),
there will be a resize_wrap_mutex.
log_t::get_lsn_approx(): Return a lower bound of get_lsn().
This should be exact unless append_prepare_wait() is pending.
log_get_lsn(): A wrapper for log_sys.get_lsn(), which must be invoked
while holding an exclusive log_sys.latch.
recv_recovery_from_checkpoint_start(): Do not invoke fil_names_clear();
it would seem to be unnecessary.
In many places, references to log_sys.get_lsn() are replaced with
log_sys.get_flushed_lsn(), which remains a simple std::atomic::load().
Reviewed by: Debarun Banerjee
acd071f599