MDEV-24109 InnoDB hangs with innodb_flush_sync=OFF

MDEV-23855 broke the handling of innodb_flush_sync=OFF.
That parameter is supposed to limit the page write rate
in case the log capacity is being exceeded and log checkpoints
are needed.

With this fix, the following should pass:
./mtr --mysqld=--loose-innodb-flush-sync=0

One of our best regression tests for page flushing is
encryption.innochecksum. With innodb_page_size=16k and
innodb_flush_sync=OFF it would likely hang without this fix.

log_sys.last_checkpoint_lsn: Declare as Atomic_relaxed<lsn_t>
so that we are allowed to read the value while not holding
log_sys.mutex.

buf_flush_wait_flushed(): Let the page cleaner perform the flushing
also if innodb_flush_sync=OFF. After the page cleaner has
completed, perform a checkpoint if it is needed, because
buf_flush_sync_for_checkpoint() will not be run if
innodb_flush_sync=OFF.

buf_flush_ahead(): Simplify the condition. We do not really care
whether buf_flush_page_cleaner() is running.

buf_flush_page_cleaner(): Evaluate innodb_flush_sync at the low
level. If innodb_flush_sync=OFF, rate-limit the batches to
innodb_io_capacity_max pages per second.

Reviewed by: Vladislav Vaintroub

include/my_atomic_wrapper.h

@@ -13,6 +13,7 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */
 
+#pragma once
 #ifdef __cplusplus
 #include <atomic>
 /**

mysql-test/include/innodb_checksum_algorithm.combinations

@@ -3,9 +3,11 @@
 
 [strict_crc32]
 --innodb-checksum-algorithm=strict_crc32
+--innodb-flush-sync=OFF
 
 [full_crc32]
 --innodb-checksum-algorithm=full_crc32
 
 [strict_full_crc32]
 --innodb-checksum-algorithm=strict_full_crc32
+--innodb-flush-sync=OFF

mysql-test/suite/sys_vars/r/innodb_flush_sync_basic.result

@@ -1,16 +1,11 @@
 SET @start_global_value = @@global.innodb_flush_sync;
-SELECT @start_global_value;
-@start_global_value
-1
 Valid values are 'ON' and 'OFF'
 select @@global.innodb_flush_sync in (0, 1);
 @@global.innodb_flush_sync in (0, 1)
 1
-select @@global.innodb_flush_sync;
-@@global.innodb_flush_sync
-1
 select @@session.innodb_flush_sync;
 ERROR HY000: Variable 'innodb_flush_sync' is a GLOBAL variable
+SET GLOBAL innodb_flush_sync = ON;
 show global variables like 'innodb_flush_sync';
 Variable_name	Value
 innodb_flush_sync	ON
@@ -87,6 +82,3 @@ INNODB_FLUSH_SYNC	ON
 set global innodb_flush_sync='AUTO';
 ERROR 42000: Variable 'innodb_flush_sync' can't be set to the value of 'AUTO'
 SET @@global.innodb_flush_sync = @start_global_value;
-SELECT @@global.innodb_flush_sync;
-@@global.innodb_flush_sync
-1

mysql-test/suite/sys_vars/t/innodb_flush_sync_basic.test

@@ -1,16 +1,15 @@
 --source include/have_innodb.inc
 
 SET @start_global_value = @@global.innodb_flush_sync;
-SELECT @start_global_value;
 
 #
 # exists as global only
 #
 --echo Valid values are 'ON' and 'OFF'
 select @@global.innodb_flush_sync in (0, 1);
-select @@global.innodb_flush_sync;
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 select @@session.innodb_flush_sync;
+SET GLOBAL innodb_flush_sync = ON;
 show global variables like 'innodb_flush_sync';
 show session variables like 'innodb_flush_sync';
 --disable_warnings
@@ -18,9 +17,6 @@ select * from information_schema.global_variables where variable_name='innodb_fl
 select * from information_schema.session_variables where variable_name='innodb_flush_sync';
 --enable_warnings
 
-#
-# show that it's writable
-#
 set global innodb_flush_sync='OFF';
 select @@global.innodb_flush_sync;
 --disable_warnings
@@ -74,4 +70,3 @@ set global innodb_flush_sync='AUTO';
 #
 
 SET @@global.innodb_flush_sync = @start_global_value;
-SELECT @@global.innodb_flush_sync;

storage/innobase/buf/buf0flu.cc

@@ -1681,52 +1681,55 @@ ATTRIBUTE_COLD void buf_flush_wait_flushed(lsn_t sync_lsn)
 
   mysql_mutex_lock(&buf_pool.flush_list_mutex);
 
+  if (buf_pool.get_oldest_modification(sync_lsn) < sync_lsn)
+  {
 #if 1 /* FIXME: remove this, and guarantee that the page cleaner serves us */
-  if (UNIV_UNLIKELY(!buf_page_cleaner_is_active)
+    if (UNIV_UNLIKELY(!buf_page_cleaner_is_active)
-      ut_d(|| innodb_page_cleaner_disabled_debug))
+        ut_d(|| innodb_page_cleaner_disabled_debug))
-  {
-    for (;;)
     {
-      const lsn_t lsn= buf_pool.get_oldest_modification(sync_lsn);
+      do
-      mysql_mutex_unlock(&buf_pool.flush_list_mutex);
-      if (lsn >= sync_lsn)
-        return;
-      ulint n_pages= buf_flush_lists(srv_max_io_capacity, sync_lsn);
-      buf_flush_wait_batch_end_acquiring_mutex(false);
-      if (n_pages)
       {
-        MONITOR_INC_VALUE_CUMULATIVE(MONITOR_FLUSH_SYNC_TOTAL_PAGE,
+        mysql_mutex_unlock(&buf_pool.flush_list_mutex);
-                                     MONITOR_FLUSH_SYNC_COUNT,
+        ulint n_pages= buf_flush_lists(srv_max_io_capacity, sync_lsn);
-                                     MONITOR_FLUSH_SYNC_PAGES, n_pages);
+        buf_flush_wait_batch_end_acquiring_mutex(false);
-        log_checkpoint();
+        if (n_pages)
+        {
+          MONITOR_INC_VALUE_CUMULATIVE(MONITOR_FLUSH_SYNC_TOTAL_PAGE,
+                                       MONITOR_FLUSH_SYNC_COUNT,
+                                       MONITOR_FLUSH_SYNC_PAGES, n_pages);
+        }
+        MONITOR_INC(MONITOR_FLUSH_SYNC_WAITS);
+        mysql_mutex_lock(&buf_pool.flush_list_mutex);
       }
-      MONITOR_INC(MONITOR_FLUSH_SYNC_WAITS);
+      while (buf_pool.get_oldest_modification(sync_lsn) < sync_lsn);
-      mysql_mutex_lock(&buf_pool.flush_list_mutex);
+
+      goto try_checkpoint;
     }
-    return;
-  }
-  else if (UNIV_LIKELY(srv_flush_sync))
 #endif
-  {
     if (buf_flush_sync_lsn < sync_lsn)
     {
       buf_flush_sync_lsn= sync_lsn;
       mysql_cond_signal(&buf_pool.do_flush_list);
     }
+
+    do
+    {
+      tpool::tpool_wait_begin();
+      thd_wait_begin(nullptr, THD_WAIT_DISKIO);
+      mysql_cond_wait(&buf_pool.done_flush_list, &buf_pool.flush_list_mutex);
+      thd_wait_end(nullptr);
+      tpool::tpool_wait_end();
+
+      MONITOR_INC(MONITOR_FLUSH_SYNC_WAITS);
+    }
+    while (buf_pool.get_oldest_modification(sync_lsn) < sync_lsn);
   }
 
-  while (buf_pool.get_oldest_modification(sync_lsn) < sync_lsn)
+try_checkpoint:
-  {
-    tpool::tpool_wait_begin();
-    thd_wait_begin(nullptr, THD_WAIT_DISKIO);
-    mysql_cond_wait(&buf_pool.done_flush_list, &buf_pool.flush_list_mutex);
-    thd_wait_end(nullptr);
-    tpool::tpool_wait_end();
-
-    MONITOR_INC(MONITOR_FLUSH_SYNC_WAITS);
-  }
-
   mysql_mutex_unlock(&buf_pool.flush_list_mutex);
+
+  if (UNIV_UNLIKELY(log_sys.last_checkpoint_lsn < sync_lsn))
+    log_checkpoint();
 }
 
 /** If innodb_flush_sync=ON, initiate a furious flush.
@@ -1739,8 +1742,7 @@ void buf_flush_ahead(lsn_t lsn)
   if (recv_recovery_is_on())
     recv_sys.apply(true);
 
-  if (buf_flush_sync_lsn < lsn &&
+  if (buf_flush_sync_lsn < lsn)
-      UNIV_LIKELY(srv_flush_sync) && UNIV_LIKELY(buf_page_cleaner_is_active))
   {
     mysql_mutex_lock(&buf_pool.flush_list_mutex);
     if (buf_flush_sync_lsn < lsn)
@@ -2054,13 +2056,15 @@ static os_thread_ret_t DECLARE_THREAD(buf_flush_page_cleaner)(void*)
     if (UNIV_UNLIKELY(lsn_limit != 0))
     {
 furious_flush:
-      buf_flush_sync_for_checkpoint(lsn_limit);
+      if (UNIV_LIKELY(srv_flush_sync))
-      last_pages= 0;
+      {
-      set_timespec(abstime, 1);
+        buf_flush_sync_for_checkpoint(lsn_limit);
-      continue;
+        last_pages= 0;
+        set_timespec(abstime, 1);
+        continue;
+      }
     }
-
+    else if (srv_shutdown_state > SRV_SHUTDOWN_INITIATED)
-    if (srv_shutdown_state > SRV_SHUTDOWN_INITIATED)
       break;
 
     mysql_cond_timedwait(&buf_pool.do_flush_list, &buf_pool.flush_list_mutex,
@@ -2070,15 +2074,25 @@ furious_flush:
     lsn_limit= buf_flush_sync_lsn;
 
     if (UNIV_UNLIKELY(lsn_limit != 0))
-      goto furious_flush;
+    {
-
+      if (UNIV_LIKELY(srv_flush_sync))
-    if (srv_shutdown_state > SRV_SHUTDOWN_INITIATED)
+        goto furious_flush;
+    }
+    else if (srv_shutdown_state > SRV_SHUTDOWN_INITIATED)
       break;
 
     const ulint dirty_blocks= UT_LIST_GET_LEN(buf_pool.flush_list);
 
     if (!dirty_blocks)
+    {
+      if (UNIV_UNLIKELY(lsn_limit != 0))
+      {
+        buf_flush_sync_lsn= 0;
+        /* wake up buf_flush_wait_flushed() */
+        mysql_cond_broadcast(&buf_pool.done_flush_list);
+      }
       continue;
+    }
 
     /* We perform dirty reads of the LRU+free list lengths here.
     Division by zero is not possible, because buf_pool.flush_list is
@@ -2086,19 +2100,29 @@ furious_flush:
     const double dirty_pct= double(dirty_blocks) * 100.0 /
       double(UT_LIST_GET_LEN(buf_pool.LRU) + UT_LIST_GET_LEN(buf_pool.free));
 
-    if (dirty_pct < srv_max_dirty_pages_pct_lwm)
+    if (dirty_pct < srv_max_dirty_pages_pct_lwm && !lsn_limit)
       continue;
 
     const lsn_t oldest_lsn= buf_pool.get_oldest_modification(0);
 
+    if (UNIV_UNLIKELY(lsn_limit != 0) && oldest_lsn >= lsn_limit)
+      buf_flush_sync_lsn= 0;
+
     mysql_mutex_unlock(&buf_pool.flush_list_mutex);
 
     ulint n_flushed;
 
-    if (!srv_adaptive_flushing)
+    if (UNIV_UNLIKELY(lsn_limit != 0))
+    {
+      n_flushed= buf_flush_lists(srv_max_io_capacity, lsn_limit);
+      /* wake up buf_flush_wait_flushed() */
+      mysql_cond_broadcast(&buf_pool.done_flush_list);
+      goto try_checkpoint;
+    }
+    else if (!srv_adaptive_flushing)
     {
       n_flushed= buf_flush_lists(srv_io_capacity, LSN_MAX);
-
+try_checkpoint:
       if (n_flushed)
       {
         MONITOR_INC_VALUE_CUMULATIVE(MONITOR_FLUSH_BACKGROUND_TOTAL_PAGE,

storage/innobase/include/log0log.h

@@ -37,7 +37,7 @@ Created 12/9/1995 Heikki Tuuri
 #include "log0types.h"
 #include "os0file.h"
 #include "span.h"
-#include <atomic>
+#include "my_atomic_wrapper.h"
 #include <vector>
 #include <string>
 
@@ -615,8 +615,8 @@ public:
 					new query step is started */
 	ib_uint64_t	next_checkpoint_no;
 					/*!< next checkpoint number */
-	lsn_t		last_checkpoint_lsn;
+  /** latest completed checkpoint (protected by log_sys.mutex) */
-					/*!< latest checkpoint lsn */
+  Atomic_relaxed<lsn_t> last_checkpoint_lsn;
 	lsn_t		next_checkpoint_lsn;
 					/*!< next checkpoint lsn */
 	ulint		n_pending_checkpoint_writes;

storage/innobase/log/log0log.cc

@@ -920,7 +920,7 @@ ATTRIBUTE_COLD void log_write_checkpoint_info(lsn_t end_lsn)
 
 	DBUG_PRINT("ib_log", ("checkpoint ended at " LSN_PF
 			      ", flushed to " LSN_PF,
-			      log_sys.last_checkpoint_lsn,
+			      lsn_t{log_sys.last_checkpoint_lsn},
 			      log_sys.get_flushed_lsn()));
 
 	MONITOR_INC(MONITOR_NUM_CHECKPOINT);
@@ -1235,7 +1235,7 @@ log_print(
 		lsn,
 		log_sys.get_flushed_lsn(),
 		pages_flushed,
-		log_sys.last_checkpoint_lsn);
+		lsn_t{log_sys.last_checkpoint_lsn});
 
 	current_time = time(NULL);