From dd5e2acab30e4be9a76e48e93b12f36913d7e863 Mon Sep 17 00:00:00 2001
From: Turan Almammadov <16321061+turanalmammadov@users.noreply.github.com>
Date: Tue, 24 Feb 2026 17:14:30 +0400
Subject: [PATCH] fix(db): add time_sensitive to oc_jobs index for maintenance
 window performance

The background job scheduler uses this query to find eligible jobs:

  SELECT * FROM oc_jobs
  WHERE reserved_at <= ?
    AND last_checked <= ?
    AND time_sensitive = ?
  ORDER BY last_checked ASC
  LIMIT ?

The previous index 'job_lastcheck_reserved' only covered (last_checked,
reserved_at), forcing a partial index scan plus individual row reads to
evaluate the time_sensitive predicate. Under heavy load this causes
unnecessary I/O especially during a maintenance window where most rows
will be filtered out by the time_sensitive condition.

Changes:
1. New migration drops 'job_lastcheck_reserved' and creates a replacement
   index 'job_lastcheck_timesens' on (last_checked, reserved_at, time_sensitive).
   The new index is a covering index for the scheduler query, eliminating
   the row-level time_sensitive evaluation entirely.

2. AddMissingIndicesListener updated to expect the new index name and columns
   so that occ db:add-missing-indices picks it up on existing installations.

Fixes: nextcloud/server#46126
Co-authored-by: Cursor <cursoragent@cursor.com>
---
 core/Listener/AddMissingIndicesListener.php   |  4 +-
 .../Version33000Date20260224000000.php        | 57 +++++++++++++++++++
 2 files changed, 59 insertions(+), 2 deletions(-)
 create mode 100644 core/Migrations/Version33000Date20260224000000.php

diff --git a/core/Listener/AddMissingIndicesListener.php b/core/Listener/AddMissingIndicesListener.php
index 27880fabeac9a..d84399993952f 100644
--- a/core/Listener/AddMissingIndicesListener.php
+++ b/core/Listener/AddMissingIndicesListener.php
@@ -152,8 +152,8 @@ public function handle(Event $event): void {
 
 		$event->addMissingIndex(
 			'jobs',
-			'job_lastcheck_reserved',
-			['last_checked', 'reserved_at']
+			'job_lastcheck_timesens',
+			['last_checked', 'reserved_at', 'time_sensitive'],
 		);
 
 		$event->addMissingIndex(
diff --git a/core/Migrations/Version33000Date20260224000000.php b/core/Migrations/Version33000Date20260224000000.php
new file mode 100644
index 0000000000000..30a8f1d1796e7
--- /dev/null
+++ b/core/Migrations/Version33000Date20260224000000.php
@@ -0,0 +1,57 @@
+<?php
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\Core\Migrations;
+
+use OCP\DB\ISchemaWrapper;
+use OCP\Migration\IOutput;
+use OCP\Migration\SimpleMigrationStep;
+
+/**
+ * Add time_sensitive column to the job_lastcheck_reserved index on oc_jobs.
+ *
+ * The cron background job scheduler query filters on three columns:
+ *   reserved_at <= ?, last_checked <= ?, AND time_sensitive = ?
+ *
+ * The old index only covered last_checked and reserved_at, forcing the
+ * database to do a full table scan to evaluate the time_sensitive predicate.
+ * Adding time_sensitive to the index allows the database to evaluate all
+ * three conditions using the index alone (covering index scan), significantly
+ * improving performance when a maintenance window is configured.
+ *
+ * @see https://github.com/nextcloud/server/issues/46126
+ */
+class Version33000Date20260224000000 extends SimpleMigrationStep {
+	public function changeSchema(IOutput $output, \Closure $schemaClosure, array $options): ?ISchemaWrapper {
+		/** @var ISchemaWrapper $schema */
+		$schema = $schemaClosure();
+
+		if (!$schema->hasTable('jobs')) {
+			return null;
+		}
+
+		$table = $schema->getTable('jobs');
+
+		// Drop the old index that only covers last_checked and reserved_at
+		if ($table->hasIndex('job_lastcheck_reserved')) {
+			$table->dropIndex('job_lastcheck_reserved');
+		}
+
+		// Recreate the index with time_sensitive included.
+		// This allows the background job scheduler query to use a full index scan
+		// instead of a partial index + row lookup, improving performance when
+		// a maintenance window restricts which jobs are eligible to run.
+		if (!$table->hasIndex('job_lastcheck_timesens')) {
+			$table->addIndex(
+				['last_checked', 'reserved_at', 'time_sensitive'],
+				'job_lastcheck_timesens',
+			);
+		}
+
+		return $schema;
+	}
+}