MDEV-25975 innodb_disallow_writes causes shutdown to hang

We will remove the parameter innodb_disallow_writes because it is badly
designed and implemented. The parameter was never allowed at startup.
It was only internally used by Galera snapshot transfer.
If a user executed
SET GLOBAL innodb_disallow_writes=ON;
the server could hang even on subsequent read operations.

During Galera snapshot transfer, we will block writes
to implement an rsync friendly snapshot, as follows:

sst_flush_tables() will acquire a global lock by executing
FLUSH TABLES WITH READ LOCK, which will block any writes
at the high level.

sst_disable_innodb_writes(), invoked via ha_disable_internal_writes(true),
will suspend or disable InnoDB background tasks or threads that could
initiate writes. As part of this, log_make_checkpoint() will be invoked
to ensure that anything in the InnoDB buf_pool.flush_list will be written
to the data files. This has the nice side effect that the Galera joiner
will avoid crash recovery.

The changes to sql/wsrep.cc and to the tests are based on a prototype
that was developed by Jan Lindström.

Reviewed by: Jan Lindström

1 files changed, 0 insertions, 12 deletions

diff --git a/extra/mariabackup/xtrabackup.cc b/extra/mariabackup/xtrabackup.cc
index 70542a35514..41461d6ece1 100644
--- a/extra/mariabackup/xtrabackup.cc
+++ b/extra/mariabackup/xtrabackup.cc
@@ -4372,11 +4372,6 @@ fail:
 	crc_init();
 	recv_sys_init();
 
-#ifdef WITH_INNODB_DISALLOW_WRITES
-	srv_allow_writes_event = os_event_create(0);
-	os_event_set(srv_allow_writes_event);
-#endif
-
 	xb_filters_init();
 
 	xb_fil_io_init();
@@ -5837,10 +5832,6 @@ static bool xtrabackup_prepare_func(char** argv)
 		log_sys.create();
 		recv_recovery_on = true;
 
-#ifdef WITH_INNODB_DISALLOW_WRITES
-		srv_allow_writes_event = os_event_create(0);
-		os_event_set(srv_allow_writes_event);
-#endif
 		dberr_t err = xb_data_files_init();
 		if (err != DB_SUCCESS) {
 			msg("mariabackup: error: xb_data_files_init() failed "
@@ -5862,9 +5853,6 @@ static bool xtrabackup_prepare_func(char** argv)
 		xb_filter_hash_free(inc_dir_tables_hash);
 
 		fil_system.close();
-#ifdef WITH_INNODB_DISALLOW_WRITES
-		os_event_destroy(srv_allow_writes_event);
-#endif
 		innodb_free_param();
 		log_sys.close();
 		sync_check_close();