Cause

When multiple sessions are inserting into a table having
auto-increment column, unique key constraint using IODKU (without
having explicit values for the auto-increment column) into a table,
the insert can fail with the unique index violation.

In such a case, the failing insert has a valid current-id for the
auto-increment column but an old/invalid value (the interleaving
session has used up the id and the failing session has not yet updated
its own next auto-increment id) as the next-id. This failed insert
updates the correct row(the row violating unique key).

The invalid value of next-id of the auto-increment column is saved and
reused as the current-id for the subsequent inserts. These subsequent
inserts, without having explicit values for the auto-increment column,
end up updating rows because of the auto-increment key violation
during the insert.

Fix

When an insert of a IODKU fails, retain the auto-increment id of the
failed row (current-id, not the next-id) to be used for next insert.

Change-Id: I7df17c90992b3658ced6d6b2a89e50546c4ce5a9