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().

1 files changed, 2 insertions, 2 deletions

diff --git a/storage/innobase/mtr/mtr0mtr.cc b/storage/innobase/mtr/mtr0mtr.cc
index 45c2ac68ef1..c058a93265c 100644
--- a/storage/innobase/mtr/mtr0mtr.cc
+++ b/storage/innobase/mtr/mtr0mtr.cc
@@ -459,7 +459,7 @@ void mtr_t::commit_files(lsn_t checkpoint_lsn)
 	if (checkpoint_lsn) {
 		DBUG_PRINT("ib_log",
 			   ("FILE_CHECKPOINT(" LSN_PF ") written at " LSN_PF,
-			    checkpoint_lsn, log_sys.lsn));
+			    checkpoint_lsn, log_sys.get_lsn()));
 	}
 }
 
@@ -589,7 +589,7 @@ inline ulint mtr_t::prepare_write()
 		ut_ad(m_log_mode == MTR_LOG_NO_REDO);
 		ut_ad(m_log.size() == 0);
 		log_mutex_enter();
-		m_commit_lsn = log_sys.lsn;
+		m_commit_lsn = log_sys.get_lsn();
 		return 0;
 	}