MDEV-33500 (part 2): rpl.rpl_parallel_sbm can still fail

The failing test case validates Seconds_Behind_Master for a delayed
slave, while STOP SLAVE is executed during a delay. The test fixes
initially added to the test (commit b04c857596) added a table lock
to ensure a transaction could not finish before validating the
Seconds_Behind_Master field after SLAVE START, but did not address a
possibility that the transaction could finish before running the
STOP SLAVE command, which invalidates the validations for the rest
of the test case. Specifically, this would result in 1) a timeout in
“Waiting for table metadata lock” on the replica, which expects the
transaction to retry after slave restart and hit a lock conflict on
the locked tables (added in b04c857596), and 2) that
Seconds_Behind_Master should have increased, but did not.

The failure can be reproduced by synchronizing the slave to the master
before the MDEV-32265 echo statement (i.e. before the SLAVE STOP).

This patch fixes the test by adding a mechanism to use DEBUG_SYNC to
synchronize a MASTER_DELAY, rather than continually increase the
duration of the delay each time the test fails on buildbot. This is
to ensure that on slow machines, a delay does not pass before the
test gets a chance to validate results. Additionally, it decreases
overall test time because the test can continue immediately after
validation, thereby bypassing the remainder of a full delay for each
transaction.

mysql-test/suite/rpl/include/sync_with_master_sql_delay_debug_sync.inc

@@ -0,0 +1,82 @@
+# ==== Purpose ====
+#
+# If using DEBUG_SYNC to coordinate a slave's SQL DELAY via the DEBUG_DBUG
+# identifier "sql_delay_by_debug_sync", this helper file will help synchronize
+# a slave with the master for statements which don't need to be delayed. This
+# can be helpful, for example, for setup/cleanup statements, if they must be
+# run in the same lifetime as the statements used for the test.
+#
+# The actual synchronization will take place based on the input parameter
+# slave_sync_method, which can be "gtid", "file_coord", or "none"; and will use
+# the helper files sync_with_master_gtid.inc or sync_with_master.inc (or none
+# at all), respectively.
+#
+#
+# ==== Requirements ====
+#
+# --source include/have_debug.inc
+# --source include/have_debug_sync.inc
+# set @@GLOBAL.debug_dbug= "+d,sql_delay_by_debug_sync";
+#
+#
+# ==== Usage ====
+#
+# --let $slave_sync_method= gtid|file_coord|none
+# [--let $num_event_groups= NUMBER]
+# --source include/sync_with_master_sql_delay_debug_sync.inc
+#
+#
+# Parameters:
+#   $slave_sync_method
+#       Value can be gtid, file_coord, or none; and will synchronize the slave
+#       with the master via this method (i.e. using sync_with_master_gtid.inc
+#       or sync_with_master.inc, respectively), after synchronizing the SQL
+#       delay
+#
+#   $num_event_groups
+#       Number of event groups to synchronize the SQL delay for. If unset, will
+#       be default to 1.
+#
+
+--let $include_filename= sync_with_master_sql_delay_debug_sync.inc
+--source include/begin_include_file.inc
+
+if (!$slave_sync_method)
+{
+  --die Parameter slave_sync_method must be set
+}
+
+if (`select "$slave_sync_method" not like "gtid" and "$slave_sync_method" not like "file_coord" and "$slave_sync_method" not like "none"`)
+{
+  --die Parameter slave_sync_method must have value "gtid", "file_coord" or "none"
+}
+
+if (`select "$slave_sync_method" not like "none" and strcmp("$master_pos", "") = 0`)
+{
+  --die sync_with_master.inc or sync_with_master_gtid.inc was not called to populate variable master_pos
+}
+
+if (!$num_event_groups)
+{
+  --let $num_event_groups= 1
+}
+
+while ($num_event_groups)
+{
+  set debug_sync= "now WAIT_FOR at_sql_delay";
+  set debug_sync= "now SIGNAL continue_sql_thread";
+  --dec $num_event_groups
+}
+
+if (`select "$slave_sync_method" LIKE "gtid"`)
+{
+  --source include/sync_with_master_gtid.inc
+}
+
+if (`select "$slave_sync_method" LIKE "file_coord"`)
+{
+  --source include/sync_with_master.inc
+}
+
+--let $include_filename= sync_with_master_sql_delay_debug_sync.inc
+--source include/end_include_file.inc

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

@@ -5,14 +5,20 @@ include/master-slave.inc
 #
 connection slave;
 include/stop_slave.inc
-set @@GLOBAL.debug_dbug= "d,negate_clock_diff_with_master";
 set @@GLOBAL.slave_parallel_mode= CONSERVATIVE;
-change master to master_delay=3, master_use_gtid=Slave_Pos;
+set @@GLOBAL.debug_dbug= "d,negate_clock_diff_with_master,sql_delay_by_debug_sync";
+change master to master_delay=1, master_use_gtid=Slave_Pos;
 include/start_slave.inc
 connection master;
 create table t1 (a int);
 create table t2 (a int);
-include/sync_slave_sql_with_master.inc
+include/save_master_gtid.inc
+connection slave;
+include/sync_with_master_sql_delay_debug_sync.inc
+set debug_sync= "now WAIT_FOR at_sql_delay";
+set debug_sync= "now SIGNAL continue_sql_thread";
+set debug_sync= "now WAIT_FOR at_sql_delay";
+set debug_sync= "now SIGNAL continue_sql_thread";
 #
 # Pt 1) Ensure SBM is updated immediately upon arrival of the next event
 connection master;
@@ -21,12 +27,23 @@ insert into t1 values (0);
 include/save_master_gtid.inc
 connection slave;
 # Waiting for transaction to arrive on slave and begin SQL Delay..
+set debug_sync= "now WAIT_FOR at_sql_delay";
 # Validating SBM is updated on event arrival..
 # ..done
 # MDEV-32265. At time of STOP SLAVE, if the SQL Thread is currently
 # delaying a transaction; then when the reciprocal START SLAVE occurs,
 # if the event is still to be delayed, SBM should resume accordingly
-include/stop_slave.inc
+connection server_2;
+# Ensure the kill from STOP SLAVE will be received before continuing the
+# SQL thread
+set debug_sync="after_thd_awake_kill SIGNAL slave_notified_of_kill";
+STOP SLAVE;
+connection slave;
+set debug_sync= "now WAIT_FOR slave_notified_of_kill";
+set debug_sync= "now SIGNAL continue_sql_thread";
+connection server_2;
+include/wait_for_slave_to_stop.inc
+set debug_sync="RESET";
 # Lock t1 on slave to ensure the event can't finish (and thereby update
 # Seconds_Behind_Master) so slow running servers don't accidentally
 # catch up to the master before checking SBM.
@@ -34,6 +51,10 @@ connection server_2;
 LOCK TABLES t1 WRITE;
 include/start_slave.inc
 connection slave;
+# SQL delay has no impact for the rest of the test case, so ignore it
+include/sync_with_master_sql_delay_debug_sync.inc
+set debug_sync= "now WAIT_FOR at_sql_delay";
+set debug_sync= "now SIGNAL continue_sql_thread";
 # Waiting for replica to get blocked by the table lock
 # Sleeping 1s to increment SBM
 # Ensuring Seconds_Behind_Master increases after sleeping..
@@ -54,6 +75,13 @@ insert into t1 values (2);
 include/save_master_pos.inc
 connection slave;
 # Wait for first transaction to complete SQL delay and begin execution..
+include/sync_with_master_sql_delay_debug_sync.inc
+set debug_sync= "now WAIT_FOR at_sql_delay";
+set debug_sync= "now SIGNAL continue_sql_thread";
+# Wait for second transaction to complete SQL delay..
+include/sync_with_master_sql_delay_debug_sync.inc
+set debug_sync= "now WAIT_FOR at_sql_delay";
+set debug_sync= "now SIGNAL continue_sql_thread";
 # Validate SBM calculation doesn't use the second transaction because worker threads shouldn't have gone idle..
 # ..and that SBM wasn't calculated using prior committed transactions
 # ..done
@@ -63,6 +91,8 @@ include/wait_for_slave_param.inc [Relay_Master_Log_File]
 include/wait_for_slave_param.inc [Exec_Master_Log_Pos]
 # Cleanup
 include/stop_slave.inc
+set debug_sync= "RESET";
+set @@GLOBAL.debug_dbug= "-d,sql_delay_by_debug_sync";
 CHANGE MASTER TO master_delay=0;
 include/start_slave.inc
 #

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

@@ -3,6 +3,7 @@
 #
 --source include/have_log_bin.inc
 --source include/have_debug.inc
+--source include/have_debug_sync.inc
 --source include/master-slave.inc
 
 --echo #
@@ -16,14 +17,23 @@
 # Seconds_Behind_Master is based on the timestamp of the new transaction,
 # rather than the last committed transaction.
 #
+#   Note that the test doesn't actually use the value of MASTER_DELAY, but
+# rather uses debug_sync to coordinate the end of the delay. This is to ensure
+# that on slow machines, a delay doesn't pass before the test gets a chance to
+# validate results. Additionally, it lets us continue testing after validation
+# so we don't have to wait out a full delay unnecessarily. The debug_sync point
+# is enabled via sql_delay_by_debug_sync, which will delay transactions based
+# only on GTID events, so only one synchronization is needed per transaction.
+#
 
 --connection slave
 --source include/stop_slave.inc
 --let $save_dbug= `SELECT @@GLOBAL.debug_dbug`
 --let $save_parallel_mode= `SELECT @@GLOBAL.slave_parallel_mode`
-set @@GLOBAL.debug_dbug= "d,negate_clock_diff_with_master";
 set @@GLOBAL.slave_parallel_mode= CONSERVATIVE;
---let $master_delay= 3
+set @@GLOBAL.debug_dbug= "d,negate_clock_diff_with_master,sql_delay_by_debug_sync";
+
+--let $master_delay= 1
 --eval change master to master_delay=$master_delay, master_use_gtid=Slave_Pos
 --source include/start_slave.inc
 
@@ -31,7 +41,11 @@ set @@GLOBAL.slave_parallel_mode= CONSERVATIVE;
 --let insert_ctr= 0
 create table t1 (a int);
 create table t2 (a int);
---source include/sync_slave_sql_with_master.inc
+--source include/save_master_gtid.inc
+--connection slave
+--let $slave_sync_method= gtid
+--let $num_event_groups= 2
+--source include/sync_with_master_sql_delay_debug_sync.inc
 
 --echo #
 --echo # Pt 1) Ensure SBM is updated immediately upon arrival of the next event
@@ -48,8 +62,7 @@ sleep 2;
 --connection slave
 
 --echo # Waiting for transaction to arrive on slave and begin SQL Delay..
---let $wait_condition= SELECT count(*) FROM information_schema.processlist WHERE state LIKE 'Waiting until MASTER_DELAY seconds after master executed event';
+set debug_sync= "now WAIT_FOR at_sql_delay";
---source include/wait_condition.inc
 
 --echo # Validating SBM is updated on event arrival..
 --let $sbm_trx1_arrive= query_get_value(SHOW SLAVE STATUS, Seconds_Behind_Master, 1)
@@ -66,7 +79,20 @@ if (`SELECT $sbm_trx1_arrive > ($seconds_since_idling + 1)`)
 --echo # delaying a transaction; then when the reciprocal START SLAVE occurs,
 --echo # if the event is still to be delayed, SBM should resume accordingly
 
---source include/stop_slave.inc
+--connection server_2
+--echo # Ensure the kill from STOP SLAVE will be received before continuing the
+--echo # SQL thread
+set debug_sync="after_thd_awake_kill SIGNAL slave_notified_of_kill";
+--send STOP SLAVE
+
+--connection slave
+set debug_sync= "now WAIT_FOR slave_notified_of_kill";
+set debug_sync= "now SIGNAL continue_sql_thread";
+
+--connection server_2
+--reap
+--source include/wait_for_slave_to_stop.inc
+set debug_sync="RESET";
 
 --echo # Lock t1 on slave to ensure the event can't finish (and thereby update
 --echo # Seconds_Behind_Master) so slow running servers don't accidentally
@@ -77,6 +103,11 @@ LOCK TABLES t1 WRITE;
 --source include/start_slave.inc
 
 --connection slave
+
+--echo # SQL delay has no impact for the rest of the test case, so ignore it
+--let $slave_sync_method= none
+--source include/sync_with_master_sql_delay_debug_sync.inc
+
 --echo # Waiting for replica to get blocked by the table lock
 --let $wait_condition= SELECT count(*) FROM information_schema.processlist WHERE state LIKE 'Waiting for table metadata lock';
 --source include/wait_condition.inc
@@ -120,9 +151,14 @@ sleep 3;
 
 --connection slave
 --echo # Wait for first transaction to complete SQL delay and begin execution..
+--let $slave_sync_method= none
+--source include/sync_with_master_sql_delay_debug_sync.inc
 --let $wait_condition= SELECT count(*) FROM information_schema.processlist WHERE state LIKE 'Waiting for table metadata lock%' AND command LIKE 'Slave_Worker';
 --source include/wait_condition.inc
 
+--echo # Wait for second transaction to complete SQL delay..
+--source include/sync_with_master_sql_delay_debug_sync.inc
+
 --echo # Validate SBM calculation doesn't use the second transaction because worker threads shouldn't have gone idle..
 --let $sbm_after_trx_no_idle= query_get_value(SHOW SLAVE STATUS, Seconds_Behind_Master, 1)
 --let $timestamp_trxpt2_arrive= `SELECT UNIX_TIMESTAMP()`
@@ -147,6 +183,8 @@ UNLOCK TABLES;
 
 --echo # Cleanup
 --source include/stop_slave.inc
+set debug_sync= "RESET";
+set @@GLOBAL.debug_dbug= "-d,sql_delay_by_debug_sync";
 --eval CHANGE MASTER TO master_delay=0
 --source include/start_slave.inc
 

sql/slave.cc

@@ -1088,6 +1088,8 @@ terminate_slave_thread(THD *thd,
     mysql_mutex_unlock(&thd->LOCK_thd_kill);
     mysql_mutex_unlock(&thd->LOCK_thd_data);
 
+    DEBUG_SYNC(current_thd, "after_thd_awake_kill");
+
     /*
       There is a small chance that slave thread might miss the first
       alarm. To protect againts it, resend the signal until it reacts
@@ -3794,13 +3796,26 @@ sql_delay_event(Log_event *ev, THD *thd, rpl_group_info *rgi)
                         sql_delay, (long)ev->when,
                         rli->mi->clock_diff_with_master,
                         (long)now, (ulonglong)sql_delay_end, (long)nap_time));
-
+    /* if using debug_sync for sql_delay, only delay once per event group */
-    if (sql_delay_end > now)
+    if (DBUG_EVALUATE_IF("sql_delay_by_debug_sync", type == GTID_EVENT,
+                         sql_delay_end > now))
     {
       DBUG_PRINT("info", ("delaying replication event %lu secs",
                           nap_time));
       rli->start_sql_delay(sql_delay_end);
       mysql_mutex_unlock(&rli->data_lock);
+
+#ifdef ENABLED_DEBUG_SYNC
+      DBUG_EXECUTE_IF("sql_delay_by_debug_sync", {
+        DBUG_ASSERT(!debug_sync_set_action(
+            thd, STRING_WITH_LEN(
+                     "now SIGNAL at_sql_delay WAIT_FOR continue_sql_thread")));
+
+        // Skip the actual sleep if using DEBUG_SYNC to coordinate SQL_DELAY
+        DBUG_RETURN(0);
+      };);
+#endif
+
       DBUG_RETURN(slave_sleep(thd, nap_time, sql_slave_killed, rgi));
     }
   }