[stable35] fix(database): skip the replica rule when no replication is configured

lib/Database/DatabaseProbe.php

@@ -209,9 +209,41 @@ private function snapshotMysql(Connection|IDBConnection $conn, string $flavour):
 			$derived['slow_query_ratio'] = $q > 0 ? $slow / $q : 0.0;
 		}
 
+		// `Slave_running` reads OFF both on a replica whose threads have
+		// stopped *and* on a server that was never pointed at a primary —
+		// the default for a standalone install.  Publish a marker that only
+		// exists in the latter's absence, so replication rules can list it
+		// in `requires` and be skipped rather than firing everywhere.
+		if ($this->hasReplicaConfigured($conn)) {
+			$derived['Replica_configured'] = 1.0;
+		}
+
 		return new Snapshot($flavour, $version, $status, $variables, $derived);
 	}
 
+	/**
+	 * Whether this server is configured as a replica.
+	 *
+	 * The status statement returns an empty result set on a server that was
+	 * never pointed at a primary.  It also needs the REPLICATION CLIENT
+	 * (BINLOG MONITOR on MariaDB) privilege; when the Nextcloud database user
+	 * lacks it we report "not a replica", so replication rules are skipped
+	 * instead of being evaluated against something we could not verify.
+	 */
+	private function hasReplicaConfigured(Connection|IDBConnection $conn): bool {
+		// `SHOW REPLICA STATUS` exists since MySQL 8.0.22 / MariaDB 10.5;
+		// older servers only know the pre-deprecation spelling.
+		foreach (['SHOW REPLICA STATUS', 'SHOW SLAVE STATUS'] as $sql) {
+			try {
+				return $this->all($conn, $sql) !== [];
+			} catch (\Throwable) {
+				// Unsupported syntax or missing privilege — try the next spelling.
+			}
+		}
+
+		return false;
+	}
+
 	// ── PostgreSQL ──────────────────────────────────────────────────
 
 	private function snapshotPostgres(Connection|IDBConnection $conn): Snapshot {

lib/Database/RuleSet/Mysql.php

@@ -384,7 +384,7 @@ private function build(): array {
 			recommendation: 'Check the replica with SHOW REPLICA STATUS; resolve any IO/SQL errors and restart replication.',
 			justification: 'Slave_running is reporting OFF.',
 			justificationFormula: '',
-			requires: ['Slave_running'],
+			requires: ['Slave_running', 'Replica_configured'],
 		);
 
 		// ── Security ────────────────────────────────────────────────

tests/lib/Database/AdvisorTest.php

@@ -0,0 +1,106 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\ServerInfo\Tests\Database;
+
+use OCA\ServerInfo\Database\Advisor;
+use OCA\ServerInfo\Database\ExpressionEvaluator;
+use OCA\ServerInfo\Database\RuleResult;
+use OCA\ServerInfo\Database\RuleSet\Mysql;
+use OCA\ServerInfo\Database\Snapshot;
+use PHPUnit\Framework\MockObject\MockObject;
+use Psr\Log\LoggerInterface;
+
+class AdvisorTest extends \Test\TestCase {
+	private LoggerInterface&MockObject $logger;
+	private Advisor $advisor;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->logger = $this->createMock(LoggerInterface::class);
+		$this->advisor = new Advisor(new ExpressionEvaluator(), $this->logger);
+	}
+
+	/**
+	 * @param array<string, scalar|null> $status
+	 * @param array<string, scalar|null> $derived
+	 */
+	private function resultFor(string $ruleId, array $status, array $derived = []): RuleResult {
+		// Well past Advisor::MIN_UPTIME_HOURS so the uptime gate never
+		// masks what a given test is actually asserting.
+		$status += ['Uptime' => 864000];
+		$derived += [
+			'value' => 0.0,
+			'Uptime_hours' => (float)$status['Uptime'] / 3600.0,
+			'Uptime_days' => (float)$status['Uptime'] / 86400.0,
+		];
+
+		$snapshot = new Snapshot(Snapshot::FLAVOUR_MARIADB, '11.8.8-MariaDB', $status, [], $derived);
+
+		foreach ($this->advisor->run(new Mysql(), $snapshot) as $result) {
+			if ($result->rule->id === $ruleId) {
+				return $result;
+			}
+		}
+
+		$this->fail("Rule '$ruleId' was not evaluated");
+	}
+
+	/**
+	 * A standalone server reports Slave_running = OFF simply because no
+	 * replication was ever set up.  Without a replica the rule has nothing
+	 * to say, so it must be skipped rather than raising an alert.
+	 */
+	public function testReplicaLagSkippedOnStandaloneServer(): void {
+		$result = $this->resultFor('Slave_lag', ['Slave_running' => 'OFF']);
+
+		$this->assertSame(RuleResult::STATUS_SKIPPED, $result->status);
+	}
+
+	/**
+	 * Enabling the binary log does not make a server a replica; the rule
+	 * must stay silent for a primary that simply writes binlogs.
+	 */
+	public function testReplicaLagSkippedOnPrimaryWithBinlogEnabled(): void {
+		$result = $this->resultFor('Slave_lag', [
+			'Slave_running' => 'OFF',
+			'Binlog_commits' => 4242,
+		]);
+
+		$this->assertSame(RuleResult::STATUS_SKIPPED, $result->status);
+	}
+
+	/**
+	 * On an actual replica whose threads have stopped, the alert is correct
+	 * and must still fire.
+	 */
+	public function testReplicaLagFailsOnStoppedReplica(): void {
+		$result = $this->resultFor(
+			'Slave_lag',
+			['Slave_running' => 'OFF'],
+			['Replica_configured' => 1.0],
+		);
+
+		$this->assertSame(RuleResult::STATUS_FAIL, $result->status);
+	}
+
+	/**
+	 * A healthy replica must not be flagged.
+	 */
+	public function testReplicaLagPassesOnRunningReplica(): void {
+		$result = $this->resultFor(
+			'Slave_lag',
+			['Slave_running' => 'ON'],
+			['Replica_configured' => 1.0],
+		);
+
+		$this->assertSame(RuleResult::STATUS_OK, $result->status);
+	}
+}