Remove alter_algorithm but keep the variable as no-op (with a warning).
The reasons for removing alter_algorithm are:
- alter_algorithm was introduced as a replacement for the
old_alter_table that was used to force the usage of the original
alter table algorithm (copy) in the cases where the new alter
algorithm did not work. The new option was added as a way to force
the usage of a specific algorithm when it should instead have made
it possible to disable algorithms that would not work for some
reason.
- alter_algorithm introduced some cases where ALTER TABLE would not
work without specifying the ALGORITHM=XXX option together with
ALTER TABLE.
- Having different values of alter_algorithm on master and slave could
cause slave to stop unexpectedly.
- ALTER TABLE FORCE, as used by mariadb-upgrade, would not always work
if alter_algorithm was set for the server.
- As part of the MDEV-33449 "improving repair of tables" it become
clear that alter- algorithm made it harder to provide a better and
more consistent ALTER TABLE FORCE and REPAIR TABLE and it would be
better to remove it.
This commit implements two phase binloggable ALTER.
When a new
@@session.binlog_alter_two_phase = YES
ALTER query gets logged in two parts, the START ALTER and the COMMIT
or ROLLBACK ALTER. START Alter is written in binlog as soon as
necessary locks have been acquired for the table. The timing is
such that any concurrent DML:s that update the same table are either
committed, thus logged into binary log having done work on the old
version of the table, or will be queued for execution on its new
version.
The "COMPLETE" COMMIT or ROLLBACK ALTER are written at the very point
of a normal "single-piece" ALTER that is after the most of
the query work is done. When its result is positive COMMIT ALTER is
written, otherwise ROLLBACK ALTER is written with specific error
happened after START ALTER phase.
Replication of two-phase binloggable ALTER is
cross-version safe. Specifically the OLD slave merely does not
recognized the start alter part, still being able to process and
memorize its gtid.
Two phase logged ALTER is read from binlog by mysqlbinlog to produce
BINLOG 'string', where 'string' contains base64 encoded
Query_log_event containing either the start part of ALTER, or a
completion part. The Query details can be displayed with `-v` flag,
similarly to ROW format events. Notice, mysqlbinlog output containing
parts of two-phase binloggable ALTER is processable correctly only by
binlog_alter_two_phase server.
@@log_warnings > 2 can reveal details of binlogging and slave side
processing of the ALTER parts.
The current commit also carries fixes to the following list of
reported bugs:
MDEV-27511, MDEV-27471, MDEV-27349, MDEV-27628, MDEV-27528.
Thanks to all people involved into early discussion of the feature
including Kristian Nielsen, those who helped to design, implement and
test: Sergei Golubchik, Andrei Elkin who took the burden of the
implemenation completion, Sujatha Sivakumar, Brandon
Nesterenko, Alice Sherepa, Ramesh Sivaraman, Jan Lindstrom.
