Before commit 6112853cda in MySQL 4.1.1
introduced the parameter innodb_file_per_table, all InnoDB data was
written to the InnoDB system tablespace (often named ibdata1).
A serious design problem is that once the system tablespace has grown to
some size, it cannot shrink even if the data inside it has been deleted.
There are also other design problems, such as the server hang MDEV-29930
that should only be possible when using innodb_file_per_table=0 and
innodb_undo_tablespaces=0 (storing both tables and undo logs in the
InnoDB system tablespace).
The parameter innodb_change_buffering was deprecated
in commit b5852ffbee.
Starting with commit baf276e6d4
(MDEV-19229) the number of innodb_undo_tablespaces can be increased,
so that the undo logs can be moved out of the system tablespace
of an existing installation.
If all these things (tables, undo logs, and the change buffer) are
removed from the InnoDB system tablespace, the only variable-size
data structure inside it is the InnoDB data dictionary.
DDL operations on .ibd files was optimized in
commit 86dc7b4d4c (MDEV-24626).
That should have removed any thinkable performance advantage of
using innodb_file_per_table=0.
Since there should be no benefit of setting innodb_file_per_table=0,
the parameter should be deprecated. Starting with MySQL 5.6 and
MariaDB Server 10.0, the default value is innodb_file_per_table=1.
The parameter innodb_stats_sample_pages became an alias for
innodb_stats_transient_sample_pages and was deprecated in
MariaDB Server 10.0. Let us finally remove that alias.
Problem was that we skipped background persistent statistics calculation
on applier nodes if thread is marked as high priority (a.k.a BF).
However, on applier nodes all DDL which is replicate will be executed
as high priority i.e BF.
Fixed by allowing background persistent statistics calculation on
applier nodes even when thread is marked as BF. This could lead
BF lock waits but for queries on that node needs that statistics.
