BUG#12400221 - 60926: BINARY LOG EVENTS LARGER THAN MAX_ALLOWED_PACKET

Problem
========
            
SQL statements close to the size of max_allowed_packet produce binary
log events larger than max_allowed_packet.
              
The reason why this failure is occuring is because the event length is
more than the total size of the max_allowed_packet + max_event_header
length. Now since the event length exceeds this size master Dump
thread is unable to send the packet on to the slave.
                      
That can happen e.g with row-based replication in Update_rows event.
            
Fix
====
          
The problem was fixed by increasing the max_allowed_packet for the
slave's threads (IO/SQL) by increasing it to 1GB.
This is done using the new server option included which is used to
regulate the max_allowed_packet of the slave thread (IO/SQL).
This causes the large packets to be received by the slave and apply
it successfully.

sql/log_event.h:
  Added the new option in the log_event.h file.
sql/mysqld.cc:
  Added a new option to the server.
sql/slave.cc:
  Increasing the session max_allowed_packet to a large value ,
  i.e. not taking global(max_allowed) into consideration, for the slave's threads.

1 files changed, 6 insertions, 5 deletions

diff --git a/sql/slave.cc b/sql/slave.cc
index 437762cc318..b555d4351c9 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -1884,8 +1884,8 @@ static int init_slave_thread(THD* thd, SLAVE_THD_TYPE thd_type)
   slave threads, since a replication event can become this much larger
   than the corresponding packet (query) sent from client to master.
 */
-  thd->variables.max_allowed_packet= global_system_variables.max_allowed_packet
-    + MAX_LOG_EVENT_HEADER;  /* note, incr over the global not session var */
+  thd->variables.max_allowed_packet= slave_max_allowed_packet;
+  thd->net.max_packet_size= slave_max_allowed_packet;
   thd->slave_thread = 1;
   thd->enable_slow_log= opt_log_slow_slave_statements;
   set_slave_thread_options(thd);
@@ -2630,6 +2630,7 @@ pthread_handler_t handle_slave_io(void *arg)
     thread, since a replication event can become this much larger than
     the corresponding packet (query) sent from client to master.
   */
+    thd->net.max_packet_size= slave_max_allowed_packet;
     mysql->net.max_packet_size= thd->net.max_packet_size+= MAX_LOG_EVENT_HEADER;
   }
   else
@@ -2761,10 +2762,10 @@ reading event"))
         switch (mysql_error_number) {
         case CR_NET_PACKET_TOO_LARGE:
           sql_print_error("\
-Log entry on master is longer than max_allowed_packet (%ld) on \
+Log entry on master is longer than slave_max_allowed_packet (%lu) on \
 slave. If the entry is correct, restart the server with a higher value of \
-max_allowed_packet",
-                          thd->variables.max_allowed_packet);
+slave_max_allowed_packet",
+                         slave_max_allowed_packet);
           mi->report(ERROR_LEVEL, ER_NET_PACKET_TOO_LARGE,
                      "%s", ER(ER_NET_PACKET_TOO_LARGE));
           goto err;