Batch in drupal7

 Basically batch is used for performing bulk action/operation on content. Here $itemchuncks has all the nodes and array_chunk is dividing it in to 20 sets of nodes, so that batch can take less time to execute.

$itemchucks = array_chunk($items, 10);

  foreach ($itemchucks as $key => $item) {  

    $operations[] = array('function_name_which_will_perform_logic', array($item));

  }

  $batch = array(

    'title' => t('Update fields'),

    'operations' => $operations,

    'init_message' => t('Updating'),

    'finished' => 'function_to_display_finished_message_of_batch',

  );

  batch_set($batch);