------------------------------------------------------------
revno: 6230
revision-id: venkatesh.duggirala@oracle.com-20141030170343-4pfljkuwt48gkerg
parent: marko.makela@oracle.com-20141030065549-onni0r95h2uc4s8w
committer: Venkatesh Duggirala<venkatesh.duggirala@oracle.com>
branch nick: mysql-5.6
timestamp: Thu 2014-10-30 22:33:43 +0530
message:
  Bug#19704825 TEMPORARY SLAVE TYPE CONVERSION TABLES RELEASED TO EARLY
  
  Problem: The memory used in preparing slave type conversion temporary table
  is getting released early and causing unexpected results
        
  Analysis: As part of bug#18770469 fix, We introduced an event
  m_event_mem_root (a special mem root), added to Log_event
  class. While server is creating the temporary table, the memory needed
  is allocated from this special mem root which will be freed in ~Log_event()
  i.e., the scope of this memroot is one event. But it could happen
  that in some cases, server might need to access this
  conversion temporary table for next following event. 
  For eg: A nested row event (insert is causing insert in a trigger)
  In this situation, the memory is getting delayed too early 
  and causing issues when the server is trying to access the temporary
  table inside the trigger.
        
  Fix: We cannot use a mem_root whose scope is limited to an event
  execution in this situation. With some further analysis, found out
  that clearing a thd->mem_root at the end of statement (upon applying
  an event which has STMT_END_F flag) will solve out of memory problem
  while running a long transactions (bug#18770469) and will also
  make this reported problem (memory is getting released early) to go away.