Problem was that tests select INFORMATION_SCHEMA.PROCESSLIST processes
from user system user and empty state. Thus, there is not clear
state for slave threads.
Changes:
- Added new status variables that store current amount of applier threads
(wsrep_applier_thread_count) and rollbacker threads
(wsrep_rollbacker_thread_count). This will make clear how many slave threads
of certain type there is.
- Added THD state "wsrep applier idle" when applier slave thread is
waiting for work. This makes finding slave/applier threads easier.
- Added force-restart option for mtr to always restart servers between tests
to avoid race on start of the test
- Added wait_condition_with_debug to wait until the passed statement returns
true, or the operation times out. If operation times out, the additional error
statement will be executed
Changes to be committed:
new file: mysql-test/include/force_restart.inc
new file: mysql-test/include/wait_condition_with_debug.inc
modified: mysql-test/mysql-test-run.pl
modified: mysql-test/suite/galera/disabled.def
modified: mysql-test/suite/galera/r/MW-336.result
modified: mysql-test/suite/galera/r/galera_kill_applier.result
modified: mysql-test/suite/galera/r/galera_var_slave_threads.result
new file: mysql-test/suite/galera/t/MW-336.cnf
modified: mysql-test/suite/galera/t/MW-336.test
modified: mysql-test/suite/galera/t/galera_kill_applier.test
modified: mysql-test/suite/galera/t/galera_parallel_autoinc_largetrx.test
modified: mysql-test/suite/galera/t/galera_parallel_autoinc_manytrx.test
modified: mysql-test/suite/galera/t/galera_var_slave_threads.test
modified: mysql-test/suite/wsrep/disabled.def
modified: mysql-test/suite/wsrep/r/variables.result
modified: mysql-test/suite/wsrep/t/variables.test
modified: sql/mysqld.cc
modified: sql/wsrep_mysqld.cc
modified: sql/wsrep_mysqld.h
modified: sql/wsrep_thd.cc
modified: sql/wsrep_var.cc
MDEV-17058: Test failure on wsrep.variables
MDEV-17060: Test failure on galera.galera_var_slave_threads
Fix incorrect calculation of increased applier (slave) threads.
Note that increase change takes effect "immediately" but we should
use proper wait condition to wait it. Reducing the number of
slave threads is not immediate as thread will only exit after a
replication event.
Two changes were made to the test:
1) Suppress warning "Refusing exit for the last slave thread."
This warning was already suppressed, but on the wrong node.
2) The test occasionally fails because it expects that the
number of applier threads changes immediately after
changing the value of ```variable wsrep_slave_threads```.
Which is not true. This patch turns snippets like this:
```
SET GLOBAL wsrep_slave_threads = x;
SELECT COUNT(*) = x FROM INFORMATION_SCHEMA.PROCESSLIST WHERE USER = 'system user';
```
Into proper wait_conditions:
```
SET GLOBAL wsrep_slave_threads = x;
let $wait_condition = SELECT COUNT(*) = x FROM ...;
--source include/wait_condition.inc
```
Note: At least one test is unstable, failing with the following:
./mtr --mysqld=--innodb-purge-threads=9 --big-test --no-reorder \
galera.galera_parallel_autoinc_largetrx galera.galera_var_slave_threads
The result difference is dependent on innodb_purge_threads.
