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, 2 deletions

diff --git a/mysql-test/suite/sys_vars/r/sysvars_innodb.result b/mysql-test/suite/sys_vars/r/sysvars_innodb.result
index ff6c6d310cf..f47c7de8132 100644
--- a/mysql-test/suite/sys_vars/r/sysvars_innodb.result
+++ b/mysql-test/suite/sys_vars/r/sysvars_innodb.result
@@ -2,9 +2,7 @@ select VARIABLE_NAME, SESSION_VALUE, DEFAULT_VALUE, VARIABLE_SCOPE, VARIABLE_TYP
 where variable_name like 'innodb%' and
 variable_name not in (
 'innodb_version',                   # always the same as the server version
-'innodb_disallow_writes',           # only available WITH_WSREP
 'innodb_numa_interleave',           # only available WITH_NUMA
-'innodb_sched_priority_cleaner',    # linux only
 'innodb_evict_tables_on_commit_debug', # one may want to override this
 'innodb_use_native_aio',            # default value depends on OS
 'innodb_buffer_pool_load_pages_abort')            # debug build only, and is only for testing