Batch gets memcache value and press the key, the order of the return code

By memcached getmulti function to batch gets the following 15 ID value.
31639,33878, 177410,9735, 589,12076, 25953,22447, 15368,15358, 33853,26658, 26659,12477, 15366

$ MD-> getmulti ($ arr_id );
The returned sequence:
Line_31639, line_33878, line_177410, line_9735, line_589, line_12076, line_25953, line_22447, line_15368, line_15358, line_33853, line_26658, line_26659, line_12477, line_15366,

A memcache return is correct, in multiple memcache when cannot be one-to-one correspondence in order to return.

When the need to use Memcached: GET_PRESERVE_ORDER to in order to return data:
$ Arrs = $ mem-> getmulti ($ arr_id, $ cas, Memcached :: GET_PRESERVE_ORDER );
The returned sequence:
Line_31639, line_33878, line_9735, line_589, line_22447, line_15358, line_33853, line_26658, line_177410, line_12076, line_25953, line_15368, line_26659, line_12477, line_15366,

This one, if have hit the variable, then $ CAs can play a role. $ CAS returned to the life of the variables, iterate over $ CAS out has hit the variables of the data, and then through the array_diff function and $ arr_id comparison take on a business trip to one by one.