Problem :
---------
This bug is filed from the base replication bug#25040331 where the
slave thread times out while INSERT operation waits on GAP lock taken
during Foreign Key validation.
The primary reason for the lock wait is because the statements are
getting replayed in different order. However, we also observed
two things ...
1. The slave thread could always use "Read Committed" isolation for
row level replication.
2. It is not necessary to have GAP locks in "READ Committed" isolation
level in innodb.
This bug is filed to address point(2) to avoid taking GAP locks during
Foreign Key validation.
Solution :
----------
Innodb is primarily designed for "Repeatable Read" and the GAP lock
behaviour is default. For "Read Committed" isolation, we have special
handling in row_search_mvcc to avoid taking the GAP lock while
scanning records.
While looking for Foreign Key, the code is following the default
behaviour taking GAP locks. The suggested fix is to avoid GAP
locking during FK validation similar to normal search operation
(row_search_mvcc) for "Read Committed" isolation level.
Reviewed-by: Sunny Bains <sunny.bains@oracle.com>
RB: 14526
The debug configuration parameter innodb_optimistic_insert_debug
which was introduced for testing corner cases in B-tree handling
had a bug in it. The value 1 would trigger an infinite sequence
of page splits.
Fix: When the value 1 is specified, disable this debug feature.
Approved by Yasufumi Kinoshita
