MDEV-35477: rpl_semi_sync_no_missed_ack_after_add_slave fails after MDEV-35109

MTR test rpl_semi_sync_no_missed_ack_after_add_slave fails on
buildbot after the preparatory commit for MDEV-35109 (5290fa043b)
which changed a sleep to a debug_sync point. The problem is that the
debug_sync point would time-out on a slave while waiting to enter
the logic to send an ACK reply. More specifically, where the test
config is a primary with two replicas, and the test waits on one of
the replicas to start sending an ACK, if the other replica was able
to receive the event and respond with an ACK before the binlog dump
thread of the timing-out server would prepare to send event, it
wouldn't set the SEMI_SYNC_NEED_ACK flag, and the replica wouldn't
even try to respond with an ACK.

Fix is to use debug_sync for both replicas such that both replicas
are held before sending their ack, so one can’t temporarily disable
semi-sync for the other before it receives the transaction.

mysql-test/suite/rpl/r/rpl_semi_sync_no_missed_ack_after_add_slave.result

@@ -3,7 +3,7 @@ connection server_1;
 set @old_enabled= @@global.rpl_semi_sync_master_enabled;
 set @old_timeout= @@global.rpl_semi_sync_master_timeout;
 set global rpl_semi_sync_master_enabled= 1;
-set global rpl_semi_sync_master_timeout= 500;
+set global rpl_semi_sync_master_timeout= 2000;
 connection server_2;
 include/stop_slave.inc
 set @old_enabled= @@global.rpl_semi_sync_slave_enabled;
@@ -14,15 +14,26 @@ include/start_slave.inc
 connection server_3;
 include/stop_slave.inc
 set @old_enabled= @@global.rpl_semi_sync_slave_enabled;
+set @old_dbug= @@global.debug_dbug;
 set global rpl_semi_sync_slave_enabled= 1;
+set global debug_dbug="+d,simulate_delay_semisync_slave_reply";
 include/start_slave.inc
 # Ensure primary recognizes both replicas are semi-sync
 connection server_1;
-connection server_1;
-create table t1 (a int);
+connection default;
+create table t1 (a int);;
+# Ensure both slaves get the event with the need_ack flag set (i.e. one
+# slave shouldn't be able to receive the event and send an ACK before
+# the dump thread for the other server prepares the event to send).
+connection server_3;
+set debug_sync= "now wait_for io_thd_at_slave_reply";
+connection server_2;
+set debug_sync= "now wait_for io_thd_at_slave_reply";
+connection server_3;
+set debug_sync= "now signal io_thd_do_reply";
+connection default;
 connection server_2;
 # Verifying server_2 did not send ACK
-set debug_sync= "now wait_for io_thd_at_slave_reply";
 connection server_3;
 # Verifying server_3 did send ACK
 connection server_1;
@@ -33,12 +44,13 @@ set debug_sync= "now signal io_thd_do_reply";
 #
 # Cleanup
 connection server_2;
+include/stop_slave.inc
 set global rpl_semi_sync_slave_enabled= @old_enabled;
 set global debug_dbug= @old_dbug;
-include/stop_slave.inc
 connection server_3;
-set global rpl_semi_sync_slave_enabled= @old_enabled;
 include/stop_slave.inc
+set global rpl_semi_sync_slave_enabled= @old_enabled;
+set global debug_dbug= @old_dbug;
 connection server_1;
 set global rpl_semi_sync_master_enabled= @old_enabled;
 set global rpl_semi_sync_master_timeout= @old_timeout;

mysql-test/suite/rpl/t/rpl_semi_sync_no_missed_ack_after_add_slave.test

@@ -26,7 +26,7 @@
 set @old_enabled= @@global.rpl_semi_sync_master_enabled;
 set @old_timeout= @@global.rpl_semi_sync_master_timeout;
 set global rpl_semi_sync_master_enabled= 1;
-set global rpl_semi_sync_master_timeout= 500;
+set global rpl_semi_sync_master_timeout= 2000; # 2s
 
 --connection server_2
 --source include/stop_slave.inc
@@ -39,7 +39,9 @@ set global debug_dbug="+d,simulate_delay_semisync_slave_reply";
 --connection server_3
 --source include/stop_slave.inc
 set @old_enabled= @@global.rpl_semi_sync_slave_enabled;
+set @old_dbug= @@global.debug_dbug;
 set global rpl_semi_sync_slave_enabled= 1;
+set global debug_dbug="+d,simulate_delay_semisync_slave_reply";
 --source include/start_slave.inc
 
 --echo # Ensure primary recognizes both replicas are semi-sync
@@ -55,13 +57,26 @@ if (`SELECT strcmp("$master_ss_status", "ON") != 0`)
   --die rpl_semi_sync_master_status should be ON to start
 }
 
---connection server_1
+--connection default
 --let $init_master_yes_tx= query_get_value(SHOW STATUS LIKE 'rpl_semi_sync_master_yes_tx', Value, 1)
-create table t1 (a int);
+--send create table t1 (a int);
+
+--echo # Ensure both slaves get the event with the need_ack flag set (i.e. one
+--echo # slave shouldn't be able to receive the event and send an ACK before
+--echo # the dump thread for the other server prepares the event to send).
+--connection server_3
+set debug_sync= "now wait_for io_thd_at_slave_reply";
+--connection server_2
+set debug_sync= "now wait_for io_thd_at_slave_reply";
+--connection server_3
+set debug_sync= "now signal io_thd_do_reply";
+
+--connection default
+--reap
+
 
 --connection server_2
 --echo # Verifying server_2 did not send ACK
-set debug_sync= "now wait_for io_thd_at_slave_reply";
 --let $slave1_sent_ack= query_get_value(SHOW STATUS LIKE 'rpl_semi_sync_slave_send_ack', Value, 1)
 if (`SELECT $slave1_sent_ack`)
 {
@@ -71,10 +86,6 @@ if (`SELECT $slave1_sent_ack`)
 
 --connection server_3
 --echo # Verifying server_3 did send ACK
---let $status_var= Rpl_semi_sync_slave_send_ack
---let $status_var_comparsion= >
---let $status_var_value= 0
---source include/wait_for_status_var.inc
 --let $slave2_sent_ack= query_get_value(SHOW STATUS LIKE 'rpl_semi_sync_slave_send_ack', Value, 1)
 if (`SELECT NOT $slave2_sent_ack`)
 {
@@ -108,13 +119,14 @@ set debug_sync= "now signal io_thd_do_reply";
 --echo # Cleanup
 
 --connection server_2
+--source include/stop_slave.inc
 set global rpl_semi_sync_slave_enabled= @old_enabled;
 set global debug_dbug= @old_dbug;
---source include/stop_slave.inc
 
 --connection server_3
-set global rpl_semi_sync_slave_enabled= @old_enabled;
 --source include/stop_slave.inc
+set global rpl_semi_sync_slave_enabled= @old_enabled;
+set global debug_dbug= @old_dbug;
 
 --connection server_1
 set global rpl_semi_sync_master_enabled= @old_enabled;