MDEV-18648: slave_parallel_mode= optimistic default in 10.5

Description:
============
To change 'CONSERVATIVE' @@global.slave_parallel_mode default to 'OPTIMISTIC'
in 10.5.

@sql/sys_vars.cc
Changed default parallel_mode to 'OPTIMISTIC'

@sql/rpl_filter.cc
Changed default parallel_mode to 'OPTIMISTIC'

@sql/mysqld.cc
Removed the initialization of 'SLAVE_PARALLEL_CONSERVATIVE' to
'opt_slave_parallel_mode' variable.

@mysql-test/suite/rpl/t/rpl_parallel_mdev6589.test
@mysql-test/suite/rpl/t/rpl_mdev6386.test
Added 'mtr' suppression to ignore 'ER_PRIOR_COMMIT_FAILED'. In case of
'OPTIMISTIC' mode if a transaction gets killed during "wait_for_prior_commit"
it results in above error "1964". Hence suppression needs to be added for this
error.

@mysql-test/suite/rpl/t/rpl_parallel_conflicts.test
Test has a 'slave.opt' which explicitly sets slave_parallel_mode to
'conservative'. When the test ends this mode conflicts with new default mode.
Hence check test case reports an error. The 'slave.opt' is removed and options
are set and reset within test.

@mysql-test/suite/multi_source/info_logs.result
@mysql-test/suite/multi_source/reset_slave.result
@mysql-test/suite/multi_source/simple.result
Result content mismatch in "show slave status" output. This is expected as new
slave_parallel_mode='OPTIMISTIC'.

@mysql-test/include/check-testcase.test
Updated default 'slave_parallel_mode' to 'optimistic'.

Refactored rpl_parallel.test into following test cases.
Test case 1: @mysql-test/suite/rpl/t/rpl_parallel_domain.test
Test case 2: @mysql-test/suite/rpl/t/rpl_parallel_domain_slave_single_grp.test
Test case 3: @mysql-test/suite/rpl/t/rpl_parallel_single_grpcmt.test
Test case 4: @mysql-test/suite/rpl/t/rpl_parallel_stop_slave.test
Test case 5: @mysql-test/suite/rpl/t/rpl_parallel_slave_bgc_kill.test
Test case 6: @mysql-test/suite/rpl/t/rpl_parallel_gco_wait_kill.test
Test case 7: @mysql-test/suite/rpl/t/rpl_parallel_free_deferred_event.test
Test case 8: @mysql-test/suite/rpl/t/rpl_parallel_missed_error_handling.test
Test case 9: @mysql-test/suite/rpl/t/rpl_parallel_innodb_lock_conflict.test
Test case 10: @mysql-test/suite/rpl/t/rpl_parallel_gtid_slave_pos_update_fail.test
Test case 11: @mysql-test/suite/rpl/t/rpl_parallel_wrong_exec_master_pos.test
Test case 12: @mysql-test/suite/rpl/t/rpl_parallel_partial_binlog_trans.test
Test case 13: @mysql-test/suite/rpl/t/rpl_parallel_ignore_error_on_rotate.test
Test case 14: @mysql-test/suite/rpl/t/rpl_parallel_wrong_binlog_order.test
Test case 15: @mysql-test/suite/rpl/t/rpl_parallel_incorrect_relay_pos.test
Test case 16: @mysql-test/suite/rpl/t/rpl_parallel_retry_deadlock.test
Test case 17: @mysql-test/suite/rpl/t/rpl_parallel_deadlock_corrupt_binlog.test
Test case 18: @mysql-test/suite/rpl/t/rpl_parallel_mode.test
Test case 19: @mysql-test/suite/rpl/t/rpl_parallel_analyze_table_hang.test
Test case 20: @mysql-test/suite/rpl/t/rpl_parallel_record_gtid_wakeup.test
Test case 21: @mysql-test/suite/rpl/t/rpl_parallel_stop_on_con_kill.test
Test case 22: @mysql-test/suite/rpl/t/rpl_parallel_rollback_assert.test

3 files changed, 3 insertions, 3 deletions

diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index b7f7615636b..09d8b4b7d1c 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -536,7 +536,7 @@ ulong stored_program_cache_size= 0;
 
 ulong opt_slave_parallel_threads= 0;
 ulong opt_slave_domain_parallel_threads= 0;
-ulong opt_slave_parallel_mode= SLAVE_PARALLEL_CONSERVATIVE;
+ulong opt_slave_parallel_mode;
 ulong opt_binlog_commit_wait_count= 0;
 ulong opt_binlog_commit_wait_usec= 0;
 ulong opt_slave_parallel_max_queued= 131072;
diff --git a/sql/rpl_filter.cc b/sql/rpl_filter.cc
index b167b849923..5d10cc661ca 100644
--- a/sql/rpl_filter.cc
+++ b/sql/rpl_filter.cc
@@ -24,7 +24,7 @@
 #define TABLE_RULE_ARR_SIZE   16
 
 Rpl_filter::Rpl_filter() : 
-  parallel_mode(SLAVE_PARALLEL_CONSERVATIVE),
+  parallel_mode(SLAVE_PARALLEL_OPTIMISTIC),
   table_rules_on(0),
   do_table_inited(0), ignore_table_inited(0),
   wild_do_table_inited(0), wild_ignore_table_inited(0)
diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index 3441a1ae4b1..0d035d002c4 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -2224,7 +2224,7 @@ static Sys_var_slave_parallel_mode Sys_slave_parallel_mode(
        "\"minimal\" only parallelizes the commit steps of transactions. "
        "\"none\" disables parallel apply completely.",
        GLOBAL_VAR(opt_slave_parallel_mode), NO_CMD_LINE,
-       slave_parallel_mode_names, DEFAULT(SLAVE_PARALLEL_CONSERVATIVE));
+       slave_parallel_mode_names, DEFAULT(SLAVE_PARALLEL_OPTIMISTIC));
 
 
 static Sys_var_bit Sys_skip_parallel_replication(