WL#4454 change sql_insert.cc::last_uniq_key to match keys in any order

Introduce a flag that will enable the REPLACE
command to work correctly with an underlying
storage engine that does not report unique key
conflicts in the ascending order.

sql/handler.h

@@ -127,6 +127,29 @@
 */
 #define HA_BINLOG_ROW_CAPABLE  (LL(1) << 34)
 #define HA_BINLOG_STMT_CAPABLE (LL(1) << 35)
+/*
+    When a multiple key conflict happens in a REPLACE command mysql
+    expects the conflicts to be reported in the ascending order of
+    key names.
+
+    For e.g.
+
+    CREATE TABLE t1 (a INT, UNIQUE (a), b INT NOT NULL, UNIQUE (b), c INT NOT
+                     NULL, INDEX(c));
+
+    REPLACE INTO t1 VALUES (1,1,1),(2,2,2),(2,1,3);
+
+    MySQL expects the conflict with 'a' to be reported before the conflict with
+    'b'.
+
+    If the underlying storage engine does not report the conflicting keys in
+    ascending order, it causes unexpected errors when the REPLACE command is
+    executed.
+
+    This flag helps the underlying SE to inform the server that the keys are not
+    ordered.
+*/
+#define HA_DUPLICATE_KEY_NOT_IN_ORDER    (LL(1) << 36)
 
 /*
   Set of all binlog flags. Currently only contain the capabilities

sql/sql_insert.cc

@@ -1322,6 +1322,23 @@ bool mysql_prepare_insert(THD *thd, TABLE_LIST *table_list,
 
 static int last_uniq_key(TABLE *table,uint keynr)
 {
+  /*
+    When an underlying storage engine informs that the unique key
+    conflicts are not reported in the ascending order by setting
+    the HA_DUPLICATE_KEY_NOT_IN_ORDER flag, we cannot rely on this
+    information to determine the last key conflict.
+   
+    The information about the last key conflict will be used to
+    do a replace of the new row on the conflicting row, rather
+    than doing a delete (of old row) + insert (of new row).
+   
+    Hence check for this flag and disable replacing the last row
+    by returning 0 always. Returning 0 will result in doing
+    a delete + insert always.
+  */
+  if (table->file->ha_table_flags() & HA_DUPLICATE_KEY_NOT_IN_ORDER)
+    return 0;
+
   while (++keynr < table->s->keys)
     if (table->key_info[keynr].flags & HA_NOSAME)
       return 0;