best setting of php apcu for 2000000 tags

Question

In my app,I want to store 2000000 (two million) tags in php apcu for performance. x……x is key and values.$ar is about 2000k keys and size is about 250MB.I want to store 1 day.

 <?php
  $ar=array("x……x"=>"x……x",…………);
  foreach($ar as $k=>$v){
   apcu_store($k,$v);
  }
  echo ok;
 ?>

This is store.php and run this.It gets no error.output"ok"

 <?php
  echo apcu_fetch("x……x");
 ?>

It gets nothing. Please why? I set memory limit to 700M in php.ini Please give best apcu setting.Thanks