At the start of mariadb-backup --backup, trigger a flush of the
InnoDB buffer pool, so that as little log as possible will have
to be copied.
The previously debug-build-only interface
SET GLOBAL innodb_log_checkpoint_now=ON;
will be made available on all builds, and
mariadb-backup --backup will invoke it, unless the option
--skip-innodb-log-checkpoint-now is specified.
Reviewed by: Vladislav Vaintroub
mariabackup does not load dictionary during backup, but it loads
tablespaces, that is why fil_system.max_assigned_id is not set with
dict_check_tablespaces_and_store_max_id(). There is no sense to issue the
warning during backup.
