MDEV-25607: Auto-generated DELETE from HEAP table can break replicationbb-10.2-MDEV-25607

Problem:
=======
The special logic used by the memory storage engine
to keep slaves in sync with the master on a restart can
break replication. In particular, after a restart, the
master writes DELETE statements in the binlog for
each MEMORY-based table so the slave can empty its
data. If the DELETE is not executable, e.g. due to
invalid triggers, the slave will error and fail, whereas
the master will never see the problem.

Solution:
=======
Instead of DELETE statements, use TRUNCATE to
keep slaves in-sync with the master, thereby bypassing
triggers.

Reviewed By:
===========
<TODO>

4 files changed, 90 insertions, 2 deletions

diff --git a/mysql-test/suite/binlog/r/memory_engine_truncates_on_restart.result b/mysql-test/suite/binlog/r/memory_engine_truncates_on_restart.result
new file mode 100644
index 00000000000..6e68fb1d262
--- /dev/null
+++ b/mysql-test/suite/binlog/r/memory_engine_truncates_on_restart.result
@@ -0,0 +1,44 @@
+include/master-slave.inc
+[connection master]
+reset master;
+create table t (val int) engine=MEMORY;
+# DELETE trigger should never be activated
+create trigger tr after delete on t for each row update t2 set val = 1;
+insert into t values (1),(2);
+connection slave;
+#
+# Check pre-restart values
+#
+connection master;
+select * from t;
+val
+1
+2
+connection slave;
+select * from t;
+val
+1
+2
+connection master;
+#
+# Restart server should empty master and slave `t`
+#
+include/rpl_restart_server.inc [server_number=1]
+insert into t values (3),(4);
+connection slave;
+#
+# Validate values after restart do not include those inserted previously
+#
+connection master;
+select * from t;
+val
+3
+4
+connection slave;
+select * from t;
+val
+3
+4
+connection master;
+drop table t;
+include/rpl_end.inc
diff --git a/mysql-test/suite/binlog/t/memory_engine_truncates_on_restart.test b/mysql-test/suite/binlog/t/memory_engine_truncates_on_restart.test
new file mode 100644
index 00000000000..c9e3fd20647
--- /dev/null
+++ b/mysql-test/suite/binlog/t/memory_engine_truncates_on_restart.test
@@ -0,0 +1,44 @@
+--source include/master-slave.inc
+
+reset master;
+
+create table t (val int) engine=MEMORY;
+
+-- echo # DELETE trigger should never be activated
+create trigger tr after delete on t for each row update t2 set val = 1;
+
+insert into t values (1),(2);
+
+--sync_slave_with_master
+
+-- echo #
+-- echo # Check pre-restart values
+-- echo #
+--connection master
+select * from t;
+--connection slave
+select * from t;
+
+--connection master
+-- echo #
+-- echo # Restart server should empty master and slave `t`
+-- echo #
+--let $rpl_server_number= 1
+--source include/rpl_restart_server.inc
+
+insert into t values (3),(4);
+
+--sync_slave_with_master
+
+-- echo #
+-- echo # Validate values after restart do not include those inserted previously
+-- echo #
+--connection master
+select * from t;
+--connection slave
+select * from t;
+
+# Cleanup
+--connection master
+drop table t;
+--source include/rpl_end.inc
diff --git a/mysql-test/suite/rpl/r/rpl_mdev382.result b/mysql-test/suite/rpl/r/rpl_mdev382.result
index ee9377906ad..c0c4bc556dc 100644
--- a/mysql-test/suite/rpl/r/rpl_mdev382.result
+++ b/mysql-test/suite/rpl/r/rpl_mdev382.result
@@ -355,7 +355,7 @@ a`
 show binlog events in 'master-bin.000002' from <binlog_start>;
 Log_name	Pos	Event_type	Server_id	End_log_pos	Info
 master-bin.000002	#	Gtid	1	#	GTID #-#-#
-master-bin.000002	#	Query	1	#	DELETE FROM `db1``; select 'oops!'`.`t``1`
+master-bin.000002	#	Query	1	#	TRUNCATE TABLE `db1``; select 'oops!'`.`t``1`
 connection slave;
 include/start_slave.inc
 connection master;
diff --git a/sql/sql_base.cc b/sql/sql_base.cc
index 11f4cb9890b..d3e605651bf 100644
--- a/sql/sql_base.cc
+++ b/sql/sql_base.cc
@@ -2796,7 +2796,7 @@ static bool open_table_entry_fini(THD *thd, TABLE_SHARE *share, TABLE *entry)
       String query(query_buf, sizeof(query_buf), system_charset_info);
 
       query.length(0);
-      query.append("DELETE FROM ");
+      query.append("TRUNCATE TABLE ");
       append_identifier(thd, &query, share->db.str, share->db.length);
       query.append(".");
       append_identifier(thd, &query, share->table_name.str,