fix(db): Let dirty writes cool off

We can assume that after a few seconds a read will be clean again.
This is helpful for false warnings in long running processes.

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Author: ChristophWurst

all_about_the_base.php

@@ -0,0 +1,23 @@
+<?php
+/*
+ * @copyright 2024 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2024 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+

lib/private/DB/Connection.php

@@ -55,7 +55,9 @@
 use OCP\IRequestId;
 use OCP\PreConditionNotMetException;
 use OCP\Profiler\IProfiler;
+use Psr\Clock\ClockInterface;
 use Psr\Log\LoggerInterface;
+use function in_array;
 
 class Connection extends PrimaryReadReplicaConnection {
 	/** @var string */
@@ -67,6 +69,8 @@ class Connection extends PrimaryReadReplicaConnection {
 	/** @var SystemConfig */
 	private $systemConfig;
 
+	private ClockInterface $clock;
+
 	private LoggerInterface $logger;
 
 	protected $lockedTable = null;
@@ -83,6 +87,7 @@ class Connection extends PrimaryReadReplicaConnection {
 
 	protected ?float $transactionActiveSince = null;
 
+	/** @var array<string, int> */
 	protected $tableDirtyWrites = [];
 
 	/**
@@ -110,6 +115,7 @@ public function __construct(
 		$this->tablePrefix = $params['tablePrefix'];
 
 		$this->systemConfig = \OC::$server->getSystemConfig();
+		$this->clock = \OCP\Server::get(ClockInterface::class);
 		$this->logger = \OC::$server->get(LoggerInterface::class);
 
 		/** @var \OCP\Profiler\IProfiler */
@@ -265,10 +271,19 @@ public function prepare($sql, $limit = null, $offset = null): Statement {
 	 */
 	public function executeQuery(string $sql, array $params = [], $types = [], QueryCacheProfile $qcp = null): Result {
 		$tables = $this->getQueriedTables($sql);
+		$now = $this->clock->now()->getTimestamp();
+		$dirtyTableWrites = [];
+		foreach ($tables as $table) {
+			$lastAccess = $this->tableDirtyWrites[$table] ?? 0;
+			// Only very recent writes are considered dirty
+			if ($lastAccess >= ($now - 3)) {
+				$dirtyTableWrites[] = $table;
+			}
+		}
 		if ($this->isTransactionActive()) {
 			// Transacted queries go to the primary. The consistency of the primary guarantees that we can not run
 			// into a dirty read.
-		} elseif (count(array_intersect($this->tableDirtyWrites, $tables)) === 0) {
+		} elseif (count($dirtyTableWrites) === 0) {
 			// No tables read that could have been written already in the same request and no transaction active
 			// so we can switch back to the replica for reading as long as no writes happen that switch back to the primary
 			// We cannot log here as this would log too early in the server boot process
@@ -280,7 +295,7 @@ public function executeQuery(string $sql, array $params = [], $types = [], Query
 				(int) ($this->systemConfig->getValue('loglevel_dirty_database_queries', null) ?? 0),
 				'dirty table reads: ' . $sql,
 				[
-					'tables' => $this->tableDirtyWrites,
+					'tables' => array_keys($this->tableDirtyWrites),
 					'reads' => $tables,
 					'exception' => new \Exception(),
 				],
@@ -335,7 +350,9 @@ public function executeUpdate(string $sql, array $params = [], array $types = []
 	 */
 	public function executeStatement($sql, array $params = [], array $types = []): int {
 		$tables = $this->getQueriedTables($sql);
-		$this->tableDirtyWrites = array_unique(array_merge($this->tableDirtyWrites, $tables));
+		foreach ($tables as $table) {
+			$this->tableDirtyWrites[$table] = $this->clock->now()->getTimestamp();
+		}
 		$sql = $this->replaceTablePrefix($sql);
 		$sql = $this->adapter->fixupStatement($sql);
 		$this->queriesExecuted++;