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Batch Processing and the Drupal Queue System ​

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Batch Processing Using the Batch API ​

Overview ​

The Batch API provides very useful functionality that lets you do work by breaking it into pieces to avoid PHP timeouts, etc. Usually, you'll do this by creating a group of node id's (often using array_chunk())to be processed and use the batch API to process those arrays (chunks) of ids. You can also provide code that will let it figure out how much work to do and stop itself.

In addition, you create a function to handle things once all the chunks are complete. You can also give the Batch API a bunch of work to do and have it figure out for itself when it is finished.

The Batch API uses the Drupal Queue system, allowing it to pick up where it left off in case of problems.

You can use the Batch API in controllers, forms, hook updates, and Drush commands. The implementation of each one is slightly different, as you can see in the examples.

Most often you start a batch from a form where you fill in some options and click a button. You can also run a batch on a controller where the batch operation starts when you point the browser at a URL. Batch operations in Drush commands are started when you type the command in the terminal.

When you run a batch process in a drush command, use drush_backend_batch_process() to kick off the batch e.g. in DirtSalesforceController.php:

php
if ($browser === FALSE) {
  drush_backend_batch_process();
}

This function will process a Drupal batch by spawning multiple Drush processes. It will make use of the drush_backend_invoke system to spawn multiple worker threads to handle the processing of the current batch, while keeping track of available memory. The batch system will process as many batch sets as possible until the entire batch has been completed or 60% of the available memory has been used.

There is BatchBuilder class for batch API which provides a more streamlined object-oriented approach to creating batches.

Batch API in forms ​

This example replaces a multivalue field with some new values processing 10 nodes at a time. The decision to process 10 at a time is arbitrary, but be aware that the more nodes you process at a time, the higher the possibility that the process will time out causing the batch will fail.

The form example is in the accompanying source and is accessed at https://d9book.ddev.site/batch-examples/batchform

The source file is at web/modules/custom/batch_examples/src/Form/BatchForm.php and is presented in pieces below:

Here is a simple form with a button used to kick off the batch operation.

php
/**
 * {@inheritdoc}
 */
public function buildForm(array $form, FormStateInterface $form_state): array {
  $form['message'] = [
    '#markup' => $this->t('Click the button below to kick off the batch!'),
  ];
  $form['actions']['#type'] = 'actions';
  $form['actions']['submit'] = [
    '#type' => 'submit',
    '#value' => $this->t('Run Batch'),
  ];

  return $form;
}

The route is:

yml
batch_examples.batch:
  path: '/batch-examples/batchform'
  defaults:
    _title: 'Batch Form'
    _form: 'Drupal\batch_examples\Form\BatchForm'
  requirements:
    _permission: 'access content'

The submitForm() method calls updateEventPresenters().

php
/**
 * {@inheritdoc}
 */
public function submitForm(array &$form, FormStateInterface $form_state): void {
  $this->updateEventPresenters();
  $this->messenger()->addStatus($this->t('The message has been sent.'));
  $form_state->setRedirect('<front>');
}

Here is the updateEventPresenters() method. Notice the $operations array, which contains the function to call to do the work of each batch as well as the list of nids to process.

php
function updateEventPresenters(): void {
  $query = \Drupal::entityQuery('node')
    ->condition('status', 1)
    ->condition('type', 'event')
    ->sort('title', 'ASC')
    ->accessCheck(TRUE);
  $nids = $query->execute();

  // Create batches.
  $chunk_size = 10;
  $chunks = array_chunk($nids, $chunk_size);
  $num_chunks = count($chunks);

  // Submit batches.
  $operations = [];
  for ($batch_id = 0; $batch_id < $num_chunks; $batch_id++) {
    $operations[] = [
      '\Drupal\batch_examples\Form\BatchForm::exampleProcessBatch',
      [
        $batch_id+1,
        $chunks[$batch_id]],
    ];
  }
  $batch = [
    'title' => $this->t('Updating Presenters'),
    'init_message' => $this->t('Starting to process events.'),
    'progress_message' => $this->t('Completed @current out of @total batches.'),
    'finished' => '\Drupal\batch_examples\Form\BatchForm::batchFinished',
    'error_message' => $this->t('Event processing has encountered an error.'),
    'operations' => $operations,
  ];
  batch_set($batch);
}

Here is the method that actually does the work. Most of the code is for information reporting. The actual work is in the foreach ($nids as $nid) loop:

php
public static function exampleProcessBatch(int $batch_id, array $nids, array &$context): void {
  if (!isset($context['sandbox']['progress'])) {
    $context['sandbox']['progress'] = 0;
    $context['sandbox']['current_node'] = 0;
    $context['sandbox']['max'] = 0;
  }
  if (!isset($context['results']['updated'])) {
    $context['results']['updated'] = 0;
    $context['results']['skipped'] = 0;
    $context['results']['failed'] = 0;
    $context['results']['progress'] = 0;
  }

  // Keep track of progress.
  $context['results']['progress'] += count($nids);
  $context['results']['process'] = 'Import request files';
  // Message above progress bar.
  $context['message'] = t('Processing batch #@batch_id batch size @batch_size for total @count items.',[
    '@batch_id' => number_format($batch_id),
    '@batch_size' => number_format(count($nids)),
    '@count' => number_format($context['sandbox']['max']),
  ]);

  foreach ($nids as $nid) {
    $filename = "";
    /** @var \Drupal\node\NodeInterface $event_node */
    $event_node = Node::load($nid);
    if ($event_node) {
      $array = ['Mary Smith', 'Fred Blue', 'Elizabeth Queen'];
      shuffle($array);
      $event_node->field_presenter = $array;
      $event_node->save();
    }
  }
}

The Form API will take care of getting the batches executed. If you aren't using a form (i.e. using a controller), you can use batch_process() like the line shown below. For this method, you specify any valid alias and the system will redirect to that alias after the batch completes.

php
// node/1 should be a valid node.
return batch_process('node/1');

Note

You can set up a $batch array with a title and a progress message with some variables that will get displayed.

Specify a finished index, which identifies a function to call after the batch is finished processing, as in the example below.

php
'finished' => '\Drupal\batch_examples\Form\BatchForm::batchFinished',

Here is the batchFinished() method, which displays and logs the results.

php
use Symfony\Component\HttpFoundation\RedirectResponse;

/**
 * Handle batch completion.
 *
 * @param bool $success
 *   TRUE if all batch API tasks were completed successfully.
 * @param array $results
 *   An array of processed node IDs.
 * @param array $operations
 *   A list of the operations that had not been completed.
 * @param string $elapsed
 *   Batch.inc kindly provides the elapsed processing time in seconds.
 */
 public static function batchFinished(bool $success, array $results, array $operations, string $elapsed): RedirectResponse {
  $messenger = \Drupal::messenger();
  if ($success) {
    $messenger->addMessage(t('@process processed @count nodes, skipped @skipped, updated @updated, failed @failed in @elapsed.', [
      '@process' => $results['process'],
      '@count' => $results['progress'],
      '@skipped' => $results['skipped'],
      '@updated' => $results['updated'],
      '@failed' => $results['failed'],
      '@elapsed' => $elapsed,
    ]));
    \Drupal::logger('d9book')->info(
      '@process processed @count nodes, skipped @skipped, updated @updated, failed @failed in @elapsed.', [
      '@process' => $results['process'],
      '@count' => $results['progress'],
      '@skipped' => $results['skipped'],
      '@updated' => $results['updated'],
      '@failed' => $results['failed'],
      '@elapsed' => $elapsed,
    ]);
  }
  else {
    // An error occurred.
    // $operations contains the operations that remained unprocessed.
    $error_operation = reset($operations);
    $message = t('An error occurred while processing %error_operation with arguments: @arguments', [
      '%error_operation' => $error_operation[0],
      '@arguments' => print_r($error_operation[1], TRUE),
    ]);
    $messenger->addError($message);
  }
  // Optionally redirect back to the form.
  return new RedirectResponse('/batch-examples/batchform');
}

Batch API in controllers ​

The Batch API is often used in connection with forms. If you're using a page callback, you will need to set up all the items, submit them to the batch API, and then call batch_process() with a url as the argument.

php
return batch_process('node/1');

After the batch is complete, Drupal will redirect you to that url. E.g. /node/1

More link

Drupal API | Batch operations

In this example of a processing function, you can see error handling, logging, and tracking while retrieving files from a remote source. This is fairly common when moving data between systems. The rest of the code is almost identical to the previous example.

php
public static function fileImportProcessBatch(int $batch_id, array $nids, array &$context): void {
  if (!isset($context['sandbox']['progress'])) {
    $context['sandbox']['progress'] = 0;
    $context['sandbox']['current_node'] = 0;
    $context['sandbox']['max'] = 0;
  }
  if (!isset($context['results']['updated'])) {
    $context['results']['updated'] = 0;
    $context['results']['skipped'] = 0;
    $context['results']['failed'] = 0;
    $context['results']['progress'] = 0;
  }
  // Total records to process for all batches.
  if (empty($context['sandbox']['max'])) {
    $query = \Drupal::entityQuery('node')
      ->condition('status', 1)
      ->condition('type', 'opinion_request');
    $total_nids = $query->execute();
    $context['sandbox']['max'] = count($total_nids);
  }

  // Keep track of progress.
  $context['results']['progress'] += count($nids);
  $context['results']['process'] = 'Import request files';
  // Message above progress bar.
  $context['message'] = t('Processing batch #@batch_id batch size @batch_size for total @count items.',[
    '@batch_id' => number_format($batch_id),
    '@batch_size' => number_format(count($nids)),
    '@count' => number_format($context['sandbox']['max']),
  ]);

  $fileRepository = \Drupal::service('file.repository');
  foreach ($nids as $nid) {
    $filename = "";
    $request_node = Node::load($nid);
    if ($request_node) {
      $file_id = $request_node->get('field_request_file')->target_id;
      if (!empty($file_id)) {
        // confirm that the file exists.
        $file = File::load($file_id);
        if ($file) {
          $uri = $file->getFileUri();
          if (file_exists($uri)) {
            $context['results']['skipped']++;
            continue;
          }
        }
      }

      //Skip retrieving file if there is no request date.
      $request_date = $request_node->get('field_request_date')->value;
      if (empty($request_date)) {
        $context['results']['skipped']++;
        continue;
      }
      $source_url = $request_node->get('field_pdf_file_with_path')->value;
      if ($source_url == "missing") {
        $context['results']['skipped']++;
        continue;
      }
      if (!empty($source_url)) {
        $filename = basename($source_url);
        if (empty($filename)) {
          \Drupal::logger('oag_opinions')
            ->error('file_import - Error retrieving file - invalid filename in' . $source_url);
          $context['results']['skipped']++;
          continue;
        }
        $file_contents = @file_get_contents($source_url);
        if ($file_contents === FALSE) {
          \Drupal::logger('oag_opinions')
            ->error('file_import - Error retrieving file ' . $source_url);
          \Drupal::messenger()->addError(t('Error retrieving file %filename.',['%filename' => $source_url]), FALSE);
          $context['results']['failed']++;
          continue;
        }
        $destination = "public://" . $filename;
        $file = null;
        try {
          $file = $fileRepository->writeData($file_contents, $destination, FileSystemInterface::EXISTS_REPLACE);
        }
        catch (FileException $e) {
          \Drupal::logger('oag_opinions')->error('file_import - Error saving file ' . $destination);
          \Drupal::messenger()->addError(t('Error saving file %filename', ['%filename' => $destination]), FALSE);
          $context['results']['failed']++;
          continue;
        }

        if (!$file) {
          $context['results']['failed']++;
          continue;
        }
        $fid = $file->id();
        $request_node->set('field_request_file', $fid);
        //$request_node->field_request_file->target_id = $fid;
        $request_node->save();
        $context['results']['updated']++;
      }
    }
  }
}

Here is the code that creates the batches and submits them.

php
public function summaryImport() {
  $this->summaryCreateBatches();
  return batch_process('/admin/content');
}

Note

If you want to execute a batch in a controller but return to the page you are already on, you can call batch_process() with the current URL as the argument. Here is an easy way to do it:

php
return batch_process(\Drupal::request()->getRequestUri());

Batch API and hook_update ​

If you want to update the default value of a field for all nodes using the Batch API and hook_update_N check out the following links:

Batch API in a drush command ​

You follow all the same procedures as shown in the form or controller style above, but to execute the batch, you need to use:

php
// Start the batch process.
  drush_backend_batch_process();

More details at Stack Exchange

Here is a complete drush command example:

php
<?php
namespace Drupal\example\Drush\Commands;
use Drupal\Core\Batch\BatchBuilder;
use Drupal\Core\Database\Connection;
use Drush\Attributes as CLI;
use Drush\Commands\DrushCommands;
use Symfony\Component\DependencyInjection\ContainerInterface;
/**
 * A Drush commandfile.
 *
 * In addition to this file, you need a drush.services.yml
 * in root of your module, and a composer.json file that provides the name
 * of the services file to use.
 */
final class ExampleCommands extends DrushCommands {
  /**
   * Constructs an ExampleCommands object.
   */
  public function __construct(
    private readonly Connection $connection,
  ) {
    parent::__construct();
  }
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static(
      $container->get('database'),
    );
  }
  /**
   * Command description here.
   */
  #[CLI\Command(name: 'example:batch-import', aliases: ['ebi'])]
  #[CLI\Usage(name: 'example:batch-import', description: 'Import data from provider with batch.')]
  public function runBatchImportData() {
    // Here, instead of $provider_data array, create your own data structure to import into nodes.
    $provider_data = [
      [
        'type' => 'article',
        'title' => 'Article 1'
        'body' => [
          'value' => 'Lorem Ipsum',
          'format' => 'full_html'
        ],
        'field_author' => [
          'target_id' => 3
        ],
      ],
      [
        'type' => 'article',
        'title' => 'Article 2'
        'body' => [
          'value' => 'Lorem Ipsum',
          'format' => 'full_html'
        ],
        'field_author' => [
          'target_id' => 5
        ],
      ],
      [
        'type' => 'article',
        'title' => 'Article 3'
        'body' => [
          'value' => 'Lorem Ipsum',
          'format' => 'full_html'
        ],
        'field_author' => [
          'target_id' => 2
        ],
      ],
    ];
    $batch = new BatchBuilder();
    foreach ($provider_data as $provider_datum) {
      //You can use $this->connection to run a DB query to check if $provider_datum['id'] exists already in the database.
      $batch->addOperation([ExampleCommands::class, 'batchImportData'], [$provider_datum]);
    }
    // We have set all operations in the batch.
    // Now we have to add more info for batch.
    $batch->setTitle('Import data from provider');
    $batch->setFinishCallback([ExampleCommands::class, 'batchFinishImportData']);
    batch_set($batch->toArray());
    $this->logger()->notice("Batch is set.");
    $this->logger()->notice("Start the batch process.");
    drush_backend_batch_process();
    return DrushCommands::EXIT_SUCCESS;
  }
  public static function batchImportData($data) {
    // The structure of $data is not valid for $node_manager->create($data), it's only for showcase.
    $node_manager = \Drupal::entityTypeManager()->getStorage('node');
    $node = $node_manager->create($data);
    $node->save();
  }
  public static function batchFinishImportData($success, array $results, array $operations, $elapsed) {
    $messenger = \Drupal::messenger();
    if ($success) {
      $messenger->addMessage(t('Processed @count nodes in @elapsed.', [
        '@count' => count($results),
        '@elapsed' => $elapsed,
      ]));
    }
  }
}

Here is another example at karimboudjema.com from 2018 not secure

Important rules about functions when using Batch API ​

All batch functions must be public static functions and all functions calling those must be explicitly namespaced like:

php
$nid = \Drupal\dirt_salesforce\Controller\DirtSalesforceController::lookupCommodityItem($commodity_item_id);

You can't use $this->my_function even if they are in the same class. Grab the namespace from the top of the PHP file you are using. In this case:

php
namespace Drupal\dirt_salesforce\Controller;

You can however refer to the functions with self:: e.g.

php
$node_to_update_dirt_contact_nid = self::getFirstRef($node_to_update, 'field_sf_dirt_contact_ref');

Looking at the source code for the Batch API ​

The source code for the Batch API is really well commented and worth reading.

Passing parameters to the functions in a batch operation ​

In this file https://git.drupalcode.org/project/drupal/-/blob/10.1.x/core/includes/form.inc#L562-678, there is an example batch that defines two operations that call my_function_1 and my_function_2. Notice how parameters can be passed to my_function_1 separated by commas. From https://git.drupalcode.org/project/drupal/blob/8.7.8/core/includes/form.inc#L570:

php
/**
 * Example:
 * @code
 * $batch = [
 *   'title' => t('Exporting'),
 *   'operations' => [
 *     ['my_function_1', [$account->id(), 'story']],
 *     ['my_function_2', []],
 *   ],
 *   'finished' => 'my_finished_callback',
 *   'file' => 'path_to_file_containing_my_functions',
 * ];
 * batch_set($batch);
 * // Only needed if not inside a form _submit handler.
 * // Setting redirect in batch_process.
 * batch_process('node/1');
 * @endcode
 */

Note

To execute the batch, the example shows a call to batch_process('node/1'). This could be any valid url alias e.g., /admin/content.

So here are the arguments for my_function_1:

php
* function my_function_1($uid, $type, &$context) {

Finishing a batch ​

You call the batch finished function with the following arguments:

php
/**
 * Handle batch completion.
 *
 * @param bool $success
 *   TRUE if all batch API tasks were completed successfully.
 * @param array $results
 *   An array of processed node IDs. - or whatever you put in $context['results'][]
 * @param array $operations
 *   A list of the operations that had NOT been completed.
 * @param $elapsed
 *   Elapsed time for processing in seconds.
 */
public static function batchFinished($success, array $results, array $operations, $elapsed) {

The results are displayed:

php
$messenger = \Drupal::messenger();
if ($success) {
  $messenger->addMessage(t('Processed @count nodes in @elapsed.', [
    '@count' => count($results),
    '@elapsed' => $elapsed,
  ]));
}

You can load the $results array with all sorts of interesting data, such as:

php
$context['results']['skipped'] = $skipped;
$context['results']['updated'] = $updated;

Batch API provides a nice way to display detailed results using code like:

php
$messenger->addMessage(t('Processed @count nodes, skipped @skipped, updated @updated in @elapsed.', [
  '@count' => $results['nodes'],
  '@skipped' => $results['skipped'],
  '@updated' => $results['updated'],
  '@elapsed' => $elapsed,
]));

Which produce the following output:

Processed 50 nodes, skipped 45, updated 5 in 3 sec.

Showing the progress of a batch ​

You can display an informative message above the progress bar this way.

I filled in the $context['sandbox']['max'] with a value, but I could have used $context['sandbox']['whole-bunch'] or any variable here.

php
$context['sandbox']['max'] = count($max_nids);

An informative message above the progress bar using number_format puts commas in the number if it is over 1,000.

php
$context['message'] = t('Processing total @count nodes',
  ['@count' => number_format($context['sandbox']['max'])]
);

Also you could show something about which batch number is running.

php
$operation_details = 'Yoyoma';
$id = 9;
$context['message'] = t('Running Batch "@id" @details',
  ['@id' => $id, '@details' => $operation_details]
);

You do have to provide your own info for the variables.

Stopping a batch dynamically ​

You can also stop the batch engine by setting $context['finished'] to TRUE. In cases where you can't easily figure out how many records need to beprocessed, you could use code like this.

php
// Inform the batch engine that we are not finished,
// and provide an estimation of the completion level we reached.
if ($context['sandbox']['progress'] != $context['sandbox']['max']) {
  $context['finished'] = ($context['sandbox']['progress'] >= $context['sandbox']['max']);
}

Queue System ​

From Alan Saunders article, December 2021:

A queue is simply a list of stuff that gets worked through one by one, one analogy could be a conveyor belt on a till in a supermarket, the cashier works through each item on the belt to scan them.

Queues are handy in Drupal for chunking up large operations, like sending emails to many people. By using a queue, you are trying to avoid overloading the servers resources which could cause the site to go offline until the resources on the server are free'd up.

From How to implement the queue worker API in Drupal 8 by Sarthak TTN, Feb 2017:

This is the submitForm() which creates an item and puts it in the queue.

php
/**
 * {@inheritdoc}
 */
public function submitForm(array &$form, FormStateInterface $form_state): void {
  /** @var QueueFactory $queue_factory */
  $queue_factory = \Drupal::service('queue');
  /** @var QueueInterface $queue */
  $queue = $queue_factory->get('email_processor');
  $item = new \stdClass();
  $item->username = $form_state->getValue('name');
  $item->email = $form_state->getValue('email');
  $item->query = $form_state->getValue('query');
  $queue->createItem($item);
}

Then you create a Queue Worker that implements ContainerFactoryPluginInterface and in the processItem() it processes a single item from the queue.

php
namespace Drupal\my_module\Plugin\QueueWorker;

use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\Core\Queue\QueueWorkerBase;
use Drupal\Core\Mail\MailManager;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * {@inheritdoc}
 */
class EmailEventBase extends QueueWorkerBase implements ContainerFactoryPluginInterface {

  /**
   * @param Drupal\Core\Mail\MailManager $mail
   *   The mail manager.
   */
  public function __construct(protected MailManager $mail) {}

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($container->get('plugin.manager.mail'));
  }

  /**
   * Processes a single item of Queue.
   */
  public function processItem($data) {
    $params['subject'] = t('query');
    $params['message'] = $data->query;
    $params['from'] = $data->email;
    $params['username'] = $data->username;
    $to = \Drupal::config('system.site')->get('mail');
    $this->mail->mail('my_module', 'query_mail', $to, 'en', $params, NULL, true);
  }
}

Then you'll need a cronEventProcessor which in annotation tells cron how often to run the job:

php
namespace Drupal\my_module\Plugin\QueueWorker;

/**
 *
 * @QueueWorker(
 * id = "email_processor",
 * title = "My custom Queue Worker",
 * cron = {"time" = 10}
 * )
 */
class CronEventProcessor extends EmailEventBase { }

There is another example of using the Queue API from Karim Boudjema - August 2018 not secure

Resources ​

Batch processing Resources ​

Queue API Resources ​