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, 3 insertions, 3 deletions

diff --git a/storage/innobase/fil/fil0fil.cc b/storage/innobase/fil/fil0fil.cc
index 129f672255b..b946ae3ae91 100644
--- a/storage/innobase/fil/fil0fil.cc
+++ b/storage/innobase/fil/fil0fil.cc
@@ -4462,12 +4462,12 @@ fil_names_dirty(
 {
 	ut_ad(log_mutex_own());
 	ut_ad(recv_recovery_is_on());
-	ut_ad(log_sys.lsn != 0);
+	ut_ad(log_sys.get_lsn() != 0);
 	ut_ad(space->max_lsn == 0);
 	ut_d(fil_space_validate_for_mtr_commit(space));
 
 	UT_LIST_ADD_LAST(fil_system.named_spaces, space);
-	space->max_lsn = log_sys.lsn;
+	space->max_lsn = log_sys.get_lsn();
 }
 
 /** Write FILE_MODIFY records when a non-predefined persistent
@@ -4478,7 +4478,7 @@ void fil_names_dirty_and_write(fil_space_t* space)
 {
 	ut_ad(log_mutex_own());
 	ut_d(fil_space_validate_for_mtr_commit(space));
-	ut_ad(space->max_lsn == log_sys.lsn);
+	ut_ad(space->max_lsn == log_sys.get_lsn());
 
 	UT_LIST_ADD_LAST(fil_system.named_spaces, space);
 	mtr_t mtr;