The test turns out to be senstive to @@global.gtid_cleanup_batch_size.
With a rather small default value of the latter
SELECTing from mysql.gtid_slave_pos may not be deterministic: tests
that run before may increase a pending for automitic deletion batch.
The test is refined to set its own value for the batch size which
is virtually unreachable.
Thanks to Kristian Nielsen for the analysis.
- mariadb-dump utility performs logical backups by producing
set of sql statements that can be executed. By enabling this
no-autocommit option, InnoDB can load the data in an efficient
way and writes the only one undo log for the whole operation.
Only first insert statement undergoes bulk insert operation,
remaining insert statement doesn't write undo log and undergoes
normal insert code path.
When mysqldump is run to dump the `mysql` system database, it generates
INSERT statements into the table `mysql.gtid_slave_pos`.
After running the backup script
those inserts did not produce the expected gtid state on slave. In
particular the maximum of mysql.gtid_slave_pos.sub_id did not make
into
rpl_global_gtid_slave_state.last_sub_id
an in-memory object that is supposed to match the current state of the
table. And that was regardless of whether --gtid option was specified
or not. Later when the backup recipient server starts as slave
in *non-gtid* mode this desychronization may lead to a duplicate key
error.
This effect is corrected for --gtid mode mysqldump/mariadb-dump only
as the following. The fixes ensure the insert block of the dump
script is followed with a "summing-up" SET @global.gtid_slave_pos
assignment.
For the implemenation part, note a deferred print-out of
SET-gtid_slave_pos and associated comments is prefered over relocating
of the entire blocks if (opt_master,slave_data &&
do_show_master,slave_status) ... because of compatiblity
concern. Namely an error inside do_show_*() is handled in the new code
the same way, as early as, as before.
A regression test can be run in how-to-reproduce mode as well.
One affected mtr test observed.
rpl_mysqldump_slave.result "mismatch" shows now the new deferring print
of SET-gtid_slave_pos policy in action.
