Drupal Update Hook Batch Template

module_template.install.php

<?php
/**
 * Template for hook_update_N() with batching.
 */
function module_template_update_7100(&$sandbox) {
  $items_per_loop = 100;

  // Initial setup.
  if (!isset($sandbox['processed'])) {
    // Load the nids to update
    $nids = db_query("select nid from {node} where type = 'TYPE'")->fetchCol();
    if (empty($nids)) {
      watchdog('mymodule', 'There are no items to process.', array(), WATCHDOG_NOTICE);
      return;
    }

    $sandbox['processed'] = 0;
    $sandbox['total'] = count($nids);
    $sandbox['nids'] = $nids;
  }

  // Process a batch of nids
  for ($i = 0; $i < $items_per_loop; $i++) {
    if ($nid = array_shift($sandbox['nids'])) {

      // Custom processing here.

    }

    $sandbox['processed']++;
  }

  // Update batch status.
  $sandbox['#finished'] = ($sandbox['processed'] >= $sandbox['total']) ? 1 : ($sandbox['processed'] / $sandbox['total']);

  $args = array(
    '!done' => $sandbox['processed'],
    '!total' => $sandbox['total'],
    '!pct' => round(($sandbox['processed'] / $sandbox['total']) * 100, 2),
  );

  return t('Completed !done/!total (!pct%)', $args);
}