In order to understand better how APC caching works you can do the following:
1. Restart web server (Apache or Nginx)
2. Create file "apc_fetch.php":
<?php
var_dump(apc_fetch(array(
'CUR_DATE_5s_1',
'CUR_DATE_5s_2',
'CUR_DATE_5s_3',
'CUR_DATE_0s_1',
'CUR_DATE_0s_2',
'CUR_DATE_0s_3',
)));
?>
3. Create file "apc_add.php":
<?php
$ttl = 5;
$key = 'CUR_DATE_5s_1';
$var = date('c');
$result = apc_add($key, $var, $ttl);
var_dump($result);
echo "\n";
$var = date('c');
$result = apc_add($key, $var, $ttl);
var_dump($result);
echo "\n";
$key = 'CUR_DATE_0s_1';
$var = date('c');
$result = apc_add($key, $var);
var_dump($result);
echo "\n";
$values = array(
'CUR_DATE_5s_2' => date('c'),
'CUR_DATE_5s_3' => rand(),
);
$result = apc_add($values, null, $ttl);
var_dump($result);
echo "\n";
$values = array(
'CUR_DATE_0s_2' => date('c'),
'CUR_DATE_0s_3' => rand(),
);
$result = apc_add($values, null);
var_dump($result);
?>
4. Run "apc_fetch.php" and "apc_add.php" several times in order to see the persistent result and how values change from one request to another.