>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3626957. --> Reported by: [fgm](https://www.drupal.org/user/27985) >>> <h3 id="summary-problem-motivation">Problem/Motivation</h3> <p><span class="drupalorg-gitlab-issue-link drupalorg-gitlab-link-wrapper"><a href="https://git.drupalcode.org/project/mongodb/-/work_items/3130220" class="drupalorg-gitlab-link">https://git.drupalcode.org/project/mongodb/-/work_items/3130220</a></span> planned two queue implementations in <code>mongodb_storage</code>: a <code>ReliableQueueInterface</code> one, and a simple <code>QueueInterface</code> one that might scale better without guaranteeing ordering, e.g. on a sharded collection.</p> <p>Only the simple one was delivered: the initial patch listed "Add Reliable queue" as a to-do, and the issue was closed after the merge.</p> <p>Today, <code>Drupal\mongodb_storage\Queue\Queue</code> implements only <code>QueueInterface</code>, while its docblock says it "provides a ReliableQueue".</p> <p>Callers still receive it when they ask for a reliable queue: <code>QueueFactory::get($name, TRUE)</code> falls back to <code>queue_service_NAME</code> and then <code>queue_default</code> when no <code>queue_reliable_service_NAME</code> is set, and the documentation recommends setting <code>queue_default</code> to <code>queue.mongodb</code>. Core does not check the interface, so such callers get a queue that does not declare the guarantees they asked for.</p> <p>One ordering difference with core is already visible: <code>Queue::claimItem()</code> sorts only on <code>created</code>, which has a one-second resolution, while core's <code>DatabaseQueue</code> orders by <code>created</code> and then <code>item_id</code>. Items created within the same second can therefore be claimed out of creation order.</p> <h3 id="summary-steps-reproduce">Steps to reproduce</h3> <p>With the module installed and configured:</p> <ol> <li>Set <code>$settings['queue_default'] = 'queue.mongodb';</code>, </li> <li>Check <code>\Drupal::queue('example', TRUE) instanceof ReliableQueueInterface</code>: it is <code>FALSE</code>.</li> </ol> <h3 id="summary-proposed-resolution">Proposed resolution</h3> <p>First check whether the current implementation provides the reliable guarantees: items claimed in creation order, and no item lost when a claim expires. Then take one of two ways.</p> <p>Implement reliable queue support:</p> <ol> <li>Add a secondary sort on <code>_id</code> in <code>claimItem()</code>, matching core's ordering by <code>created</code> then <code>item_id</code>.</li> <li>Declare <code>ReliableQueueInterface</code> on the existing class, or add a separate reliable implementation if the existing one cannot provide the guarantees.</li> <li>Document the reliable queue settings (<code>queue_reliable_service_NAME</code>) next to the existing <code>queue_default</code> instructions.</li> </ol> <p>Or document the lack of reliable queue support:</p> <ol> <li>Correct the <code>Queue</code> docblock, which currently claims a ReliableQueue.</li> <li>Document that <code>queue_default</code> also serves callers asking for a reliable queue, and that such queues must be kept on a reliable implementation with <code>queue_reliable_service_NAME</code>, e.g. <code>queue.database</code>.</li> </ol> <p>The unordered, possibly sharded variant from <span class="drupalorg-gitlab-issue-link drupalorg-gitlab-link-wrapper"><a href="https://git.drupalcode.org/project/mongodb/-/work_items/3130220" class="drupalorg-gitlab-link">https://git.drupalcode.org/project/mongodb/-/work_items/3130220</a></span> is left for a separate issue, if still wanted.</p> <h3 id="summary-remaining-tasks">Remaining tasks</h3> <ul> <li>Decide between the two ways, after checking the guarantees.</li> <li>If implementing: tests for claim ordering, including items created within the same second, and for items whose claim expired becoming claimable again.</li> <li>MR.</li> <li>Documentation update, in either case.</li> </ul> <h3 id="summary-ui-changes">User interface changes</h3> <p>None.</p> <h3 id="summary-api-changes">API changes</h3> <p>If implementing on the existing class: <code>Queue</code> also implements <code>ReliableQueueInterface</code>, an addition that does not break callers. If documenting the lack: none.</p> <h3 id="summary-data-model-changes">Data model changes</h3> <p>None expected. If implementing, the ordering fix may warrant an index on <code>created</code> and <code>_id</code>, to be checked against the existing indexes.</p> <h3 id="summary-ai-disclosure">AI disclosure</h3> <p>Issue generated with AI assistance. Developers implementing the feature may use AI and will need to edit this section accordingly.</p>