BUG#17018343 SLAVE CRASHES WHEN APPLYING ROW-BASED BINLOG ENTRIES IN CASCADING

REPLICATION

Problem: In RBR mode, merge table updates are not successfully applied on a cascading
replication.

Analysis & Fix: Every type of row event is preceded by one or more table_map_log_events
that gives the information about all the tables that are involved in the row
event. Server maintains the list in RPL_TABLE_LIST and it goes through all the
tables and checks for the compatibility between master and slave. Before
checking for the compatibility, it calls 'open_tables()' which takes the list
of all tables that needs to be locked and opened. In RBR, because of the
Table_map_log_event , we already have all the tables including base tables in
the list. But the open_tables() which is generic call takes care of appending
base tables if the list contains merge tables. There is an assumption in the
current replication layer logic that these tables (TABLE_LIST type objects) are always
added in the end of the list. Replication layer maintains the count of
tables(tables_to_lock_count) that needs to be verified for compatibility check
and runs through only those many tables from the list and rest of the objects
in linked list can be skipped. But this assumption is wrong.
open_tables()->..->add_children_to_list() adds base tables to the list immediately
after seeing the merge table in the list.

For eg: If the list passed to open_tables() is t1->t2->t3 where t3 is merge
table (and t1 and t2 are base tables), it adds t1'->t2' to the list after t3.
New table list looks like t1->t2->t3->t1'->t2'. It looks like it added at the
end of the list but that is not correct. If the list passed to open_tables()
is t3->t1->t2 where t3 is merge table (and t1 and t2 are base tables), the new
prepared list will be t3->t1'->t2'->t1->t2. Where t1' and t2' are of
TABLE_LIST objects which were added by add_children_to_list() call and replication
layer should not look into them. Here tables_to_lock_count  will not help as the
objects are added in between the list.

Fix: After investigating add_children_list() logic (which is called from open_tables()),
there is no flag/logic in it to skip adding the children to the list even if the
children are already included in the table list. Hence to fix the issue, a
logic should be added in the replication layer to skip children in the list by
checking whether  'parent_l' is non-null or not. If it is children, we will skip 'compatibility'
check for that table.

Also this patch is not removing 'tables_to_lock_count' logic for the performance issues
if there are any children at the end of the list, those can be easily skipped directly by
stopping the loop with tables_to_lock_count check.

1 files changed, 39 insertions, 7 deletions

diff --git a/sql/log_event.cc b/sql/log_event.cc
index accb6a28dbd..702cf1d575a 100644
--- a/sql/log_event.cc
+++ b/sql/log_event.cc
@@ -1,5 +1,5 @@
 /*
-   Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.
+   Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -7930,9 +7930,6 @@ int Rows_log_event::do_apply_event(Relay_log_info const *rli)
     /*
       When the open and locking succeeded, we check all tables to
       ensure that they still have the correct type.
-
-      We can use a down cast here since we know that every table added
-      to the tables_to_lock is a RPL_TABLE_LIST.
     */
 
     {
@@ -7951,10 +7948,37 @@ int Rows_log_event::do_apply_event(Relay_log_info const *rli)
         NOTE: The base tables are added here are removed when 
               close_thread_tables is called.
        */
-      RPL_TABLE_LIST *ptr= rli->tables_to_lock;
-      for (uint i= 0 ; ptr && (i < rli->tables_to_lock_count);
-           ptr= static_cast<RPL_TABLE_LIST*>(ptr->next_global), i++)
+      TABLE_LIST *table_list_ptr= rli->tables_to_lock;
+      for (uint i=0 ; table_list_ptr && (i < rli->tables_to_lock_count);
+           table_list_ptr= table_list_ptr->next_global, i++)
       {
+        /*
+          Below if condition takes care of skipping base tables that
+          make up the MERGE table (which are added by open_tables()
+          call). They are added next to the merge table in the list.
+          For eg: If RPL_TABLE_LIST is t3->t1->t2 (where t1 and t2
+          are base tables for merge table 't3'), open_tables will modify
+          the list by adding t1 and t2 again immediately after t3 in the
+          list (*not at the end of the list*). New table_to_lock list will
+          look like t3->t1'->t2'->t1->t2 (where t1' and t2' are TABLE_LIST
+          objects added by open_tables() call). There is no flag(or logic) in
+          open_tables() that can skip adding these base tables to the list.
+          So the logic here should take care of skipping them.
+
+          tables_to_lock_count logic will take care of skipping base tables
+          that are added at the end of the list.
+          For eg: If RPL_TABLE_LIST is t1->t2->t3, open_tables will modify
+          the list into t1->t2->t3->t1'->t2'. t1' and t2' will be skipped
+          because tables_to_lock_count logic in this for loop.
+        */
+        if (table_list_ptr->parent_l)
+          continue;
+        /*
+          We can use a down cast here since we know that every table added
+          to the tables_to_lock is a RPL_TABLE_LIST (or child table which is
+          skipped above).
+        */
+        RPL_TABLE_LIST *ptr= static_cast<RPL_TABLE_LIST*>(table_list_ptr);
         DBUG_ASSERT(ptr->m_tabledef_valid);
         TABLE *conv_table;
         if (!ptr->m_tabledef.compatible_with(thd, const_cast<Relay_log_info*>(rli),
@@ -7995,7 +8019,15 @@ int Rows_log_event::do_apply_event(Relay_log_info const *rli)
      */
     TABLE_LIST *ptr= rli->tables_to_lock;
     for (uint i=0 ;  ptr && (i < rli->tables_to_lock_count); ptr= ptr->next_global, i++)
+    {
+      /*
+        Please see comment in above 'for' loop to know the reason
+        for this if condition
+      */
+      if (ptr->parent_l)
+        continue;
       const_cast<Relay_log_info*>(rli)->m_table_map.set_table(ptr->table_id, ptr->table);
+    }
 
 #ifdef HAVE_QUERY_CACHE
     query_cache.invalidate_locked_for_write(rli->tables_to_lock);