MDEV-16146: MariaDB slave stops with following errors.

Problem:
========
180511 11:07:58 [ERROR] Slave I/O: Unexpected master's heartbeat data:
heartbeat is not compatible with local info;the event's data: log_file_name
mysql-bin.000009 log_pos 1054262041, Error_code: 1623

Analysis:
=========
In replication setup when master server doesn't have any events to send to
slave server it sends an 'Heartbeat_log_event'. This event carries the
current binary log filename and offset details. The offset values is stored
within 4 bytes of event header. When the size of binary log is higher than
UINT32_MAX the log_pos values will not fit in 4 bytes memory.  It overflows
and hence slave stops with an error.

Fix:
===
Since we cannot extend the common_header of Log_event class, a greater than
4GB value of Log_event::log_pos is made to be transported with a HeartBeat
event's sub-header.  Log_event::log_pos in such case is set to zero to
indicate that the 8 byte sub-header is allocated in the event.

In case of cross version replication following behaviour is expected

OLD - Server without fix
NEW - Server with fix

OLD<->NEW : works bidirectionally as long as the binlog offset is
            (normally) within 4GB.

When log_pos > UINT32_MAX
OLD->NEW  : The 'log_pos' is bound to overflow and NEW slave may report
            an invalid event/incompatible heart beat event error.
NEW->OLD  : Since patched server sets log_pos=0 on overflow, OLD slave will
            report invalid event error.

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

+include/master-slave.inc
+[connection master]
+connection master;
+SET @saved_dbug = @@GLOBAL.debug_dbug;
+SET @@global.debug_dbug= 'd,simulate_pos_4G';
+connection slave;
+include/stop_slave.inc
+CHANGE MASTER TO MASTER_HEARTBEAT_PERIOD=0.001;
+include/start_slave.inc
+connection master;
+SET @@GLOBAL.debug_dbug = @saved_dbug;
+connection slave;
+connection master;
+CREATE TABLE t (f INT) ENGINE=INNODB;
+INSERT INTO t VALUES (10);
+DROP TABLE t;
+include/rpl_end.inc

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

+# ==== Purpose ====
+#
+# Test verifies that slave IO thread can process heartbeat events with log_pos
+# values higher than UINT32_MAX.
+#
+# ==== Implementation ====
+#
+# Steps:
+#    0 - Stop slave threads. Configure a small master_heartbeat_period.
+#    1 - Using debug points, simulate a huge binlog offset higher than
+#        UINT32_MAX on master.
+#    2 - Start the slave and observe that slave IO thread is able to process
+#        the offset received through heartbeat event.
+#
+# ==== References ====
+#
+# MDEV-16146: MariaDB slave stops with incompatible heartbeat
+#
+--source include/have_debug.inc
+--source include/have_innodb.inc
+--source include/have_binlog_format_mixed.inc
+# Test simulates binarylog offsets higher than UINT32_MAX
+--source include/have_64bit.inc
+--source include/master-slave.inc
+
+--connection master
+SET @saved_dbug = @@GLOBAL.debug_dbug;
+SET @@global.debug_dbug= 'd,simulate_pos_4G';
+
+--connection slave
+--source include/stop_slave.inc
+CHANGE MASTER TO MASTER_HEARTBEAT_PERIOD=0.001;
+--source include/start_slave.inc
+
+--connection master
+sleep 1;
+SET @@GLOBAL.debug_dbug = @saved_dbug;
+--sync_slave_with_master
+
+--connection master
+CREATE TABLE t (f INT) ENGINE=INNODB;
+INSERT INTO t VALUES (10);
+DROP TABLE t;
+--source include/rpl_end.inc

sql/log_event.cc

@@ -14324,14 +14324,23 @@ st_print_event_info::st_print_event_info()
 #endif
 
 #if defined(HAVE_REPLICATION) && !defined(MYSQL_CLIENT)
-Heartbeat_log_event::Heartbeat_log_event(const char* buf, uint event_len,
+Heartbeat_log_event::Heartbeat_log_event(const char* buf, ulong event_len,
                     const Format_description_log_event* description_event)
   :Log_event(buf, description_event)
 {
   uint8 header_size= description_event->common_header_len;
-  ident_len = event_len - header_size;
-  set_if_smaller(ident_len,FN_REFLEN-1);
-  log_ident= buf + header_size;
+  if (log_pos == 0)
+  {
+    log_pos= uint8korr(buf + header_size);
+    log_ident= buf + header_size + HB_SUB_HEADER_LEN;
+    ident_len= event_len - (header_size + HB_SUB_HEADER_LEN);
+  }
+  else
+  {
+    log_ident= buf + header_size;
+    ident_len = event_len - header_size;
+  }
+
 }
 #endif
 

sql/log_event.h

@@ -570,6 +570,14 @@ class String;
 #define MARIA_SLAVE_CAPABILITY_MINE MARIA_SLAVE_CAPABILITY_GTID
 
 
+/*
+  When the size of 'log_pos' within Heartbeat_log_event exceeds UINT32_MAX it
+  cannot be accommodated in common_header, as 'log_pos' is of 4 bytes size. In
+  such cases, sub_header, of size 8 bytes will hold larger 'log_pos' value.
+*/
+#define HB_SUB_HEADER_LEN 8
+
+
 /**
   @enum Log_event_type
 
@@ -5160,12 +5168,13 @@ static inline bool copy_event_cache_to_file_and_reinit(IO_CACHE *cache,
 class Heartbeat_log_event: public Log_event
 {
 public:
-  Heartbeat_log_event(const char* buf, uint event_len,
+  uint8 hb_flags;
+  Heartbeat_log_event(const char* buf, ulong event_len,
                       const Format_description_log_event* description_event);
   Log_event_type get_type_code() { return HEARTBEAT_LOG_EVENT; }
   bool is_valid() const
     {
-      return (log_ident != NULL &&
+      return (log_ident != NULL && ident_len <= FN_REFLEN-1 &&
               log_pos >= BIN_LOG_HEADER_SIZE);
     }
   const char * get_log_ident() { return log_ident; }

sql/sql_repl.cc

@@ -32,6 +32,7 @@
 #include "debug_sync.h"
 #include "log.h"                                // get_gtid_list_event
 
+
 enum enum_gtid_until_state {
   GTID_UNTIL_NOT_DONE,
   GTID_UNTIL_STOP_AFTER_STANDALONE,
@@ -781,7 +782,7 @@ get_slave_until_gtid(THD *thd, String *out_str)
   @param event_coordinates  binlog file name and position of the last
                             real event master sent from binlog
 
-  @note 
+  @note
     Among three essential pieces of heartbeat data Log_event::when
     is computed locally.
     The  error to send is serious and should force terminating
@@ -795,6 +796,8 @@ static int send_heartbeat_event(binlog_send_info *info,
   DBUG_ENTER("send_heartbeat_event");
 
   ulong ev_offset;
+  char sub_header_buf[HB_SUB_HEADER_LEN];
+  bool sub_header_in_use=false;
   if (reset_transmit_packet(info, info->flags, &ev_offset, &info->errmsg))
     DBUG_RETURN(1);
 
@@ -815,18 +818,38 @@ static int send_heartbeat_event(binlog_send_info *info,
   ulong event_len = ident_len + LOG_EVENT_HEADER_LEN +
     (do_checksum ? BINLOG_CHECKSUM_LEN : 0);
   int4store(header + SERVER_ID_OFFSET, global_system_variables.server_id);
+  DBUG_EXECUTE_IF("simulate_pos_4G",
+  {
+    const_cast<event_coordinates *>(coord)->pos= (UINT_MAX32 + (ulong)1);
+    DBUG_SET("-d, simulate_pos_4G");
+  };);
+  if (coord->pos <= UINT_MAX32)
+  {
+    int4store(header + LOG_POS_OFFSET, coord->pos);  // log_pos
+  }
+  else
+  {
+    // Set common_header.log_pos=0 to indicate its overflow
+    int4store(header + LOG_POS_OFFSET, 0);
+    sub_header_in_use= true;
+    int8store(sub_header_buf, coord->pos);
+    event_len+= HB_SUB_HEADER_LEN;
+  }
+
   int4store(header + EVENT_LEN_OFFSET, event_len);
   int2store(header + FLAGS_OFFSET, 0);
 
-  int4store(header + LOG_POS_OFFSET, coord->pos);  // log_pos
-
   packet->append(header, sizeof(header));
-  packet->append(p, ident_len);             // log_file_name
+  if (sub_header_in_use)
+    packet->append(sub_header_buf, sizeof(sub_header_buf));
+  packet->append(p, ident_len);                    // log_file_name
 
   if (do_checksum)
   {
     char b[BINLOG_CHECKSUM_LEN];
     ha_checksum crc= my_checksum(0, (uchar*) header, sizeof(header));
+    if (sub_header_in_use)
+      crc= my_checksum(crc, (uchar*) sub_header_buf, sizeof(sub_header_buf));
     crc= my_checksum(crc, (uchar*) p, ident_len);
     int4store(b, crc);
     packet->append(b, sizeof(b));