MDEV-14425 Cleanup: Use std::atomic for some log_sys members

Some fields were protected by log_sys.mutex, which adds quite some
overhead for readers. Some readers were submitting dirty reads.

log_t::lsn: Declare private and atomic. Add wrappers get_lsn()
and set_lsn() that will use relaxed memory access. Many accesses
to log_sys.lsn are still protected by log_sys.mutex; we avoid the
mutex for some readers.

log_t::flushed_to_disk_lsn: Declare private and atomic, and move
to the same cache line with log_t::lsn.

log_t::buf_free: Declare as size_t, and move to the same cache line
with log_t::lsn.

log_t::check_flush_or_checkpoint_: Declare private and atomic,
and move to the same cache line with log_t::lsn.

log_get_lsn(): Define as an alias of log_sys.get_lsn().

log_get_lsn_nowait(), log_peek_lsn(): Remove.

log_get_flush_lsn(): Define as an alias of log_sys.get_flush_lsn().

log_t::initiate_write(): Replaces log_buffer_sync_in_background().

0 files changed, 0 insertions, 0 deletions