enh: Implement PrimaryReadReplicaConnection

Signed-off-by: Julius Härtl <jus@bitgrid.net>

config/config.sample.php

@@ -151,6 +151,14 @@
  */
 'dbpersistent' => '',
 
+/**
+ * Specify read only replicas to be used by Nextcloud when querying the database
+ */
+'dbreplica' => [
+	['user' => 'replica1', 'password', 'host' => '', 'dbname' => ''],
+	['user' => 'replica1', 'password', 'host' => '', 'dbname' => ''],
+],
+
 /**
  * Indicates whether the Nextcloud instance was installed successfully; ``true``
  * indicates a successful installation, and ``false`` indicates an unsuccessful

lib/private/DB/Connection.php

@@ -38,6 +38,7 @@
 use Doctrine\Common\EventManager;
 use Doctrine\DBAL\Cache\QueryCacheProfile;
 use Doctrine\DBAL\Configuration;
+use Doctrine\DBAL\Connections\PrimaryReadReplicaConnection;
 use Doctrine\DBAL\Driver;
 use Doctrine\DBAL\Exception;
 use Doctrine\DBAL\Platforms\MySQLPlatform;
@@ -55,7 +56,7 @@
 use OCP\Profiler\IProfiler;
 use Psr\Log\LoggerInterface;
 
-class Connection extends \Doctrine\DBAL\Connection {
+class Connection extends PrimaryReadReplicaConnection {
 	/** @var string */
 	protected $tablePrefix;
 
@@ -119,7 +120,7 @@ public function __construct(
 	/**
 	 * @throws Exception
 	 */
-	public function connect() {
+	public function connect($connectionName = null) {
 		try {
 			if ($this->_conn) {
 				/** @psalm-suppress InternalMethod */
@@ -302,6 +303,10 @@ protected function logQueryToFile(string $sql): void {
 				$prefix .= \OC::$server->get(IRequestId::class)->getId() . "\t";
 			}
 
+			// FIXME:  Improve to log the actual target db host
+			$isPrimary = $this->connections['primary'] === $this->_conn;
+			$prefix .= ' ' . ($isPrimary === true ? 'primary' : 'replica') . ' ';
+
 			file_put_contents(
 				$this->systemConfig->getValue('query_log_file', ''),
 				$prefix . $sql . "\n",
@@ -603,4 +608,14 @@ private function getMigrator() {
 			return new Migrator($this, $config, $dispatcher);
 		}
 	}
+
+	protected function performConnect(?string $connectionName = null): bool {
+		$before = $this->isConnectedToPrimary();
+		$result = parent::performConnect($connectionName);
+		$after = $this->isConnectedToPrimary();
+		if (!$before && $after) {
+			$this->logger->debug('Switched to primary database', ['exception' => new \Exception()]);
+		}
+		return $result;
+	}
 }

lib/private/DB/ConnectionFactory.php

@@ -32,7 +32,6 @@
 use Doctrine\DBAL\Configuration;
 use Doctrine\DBAL\DriverManager;
 use Doctrine\DBAL\Event\Listeners\OracleSessionInit;
-use Doctrine\DBAL\Event\Listeners\SQLSessionInit;
 use OC\SystemConfig;
 
 /**
@@ -127,11 +126,8 @@ public function getConnection($type, $additionalConnectionParams) {
 		$normalizedType = $this->normalizeType($type);
 		$eventManager = new EventManager();
 		$eventManager->addEventSubscriber(new SetTransactionIsolationLevel());
+		$additionalConnectionParams = array_merge($this->createConnectionParams(), $additionalConnectionParams);
 		switch ($normalizedType) {
-			case 'mysql':
-				$eventManager->addEventSubscriber(
-					new SQLSessionInit("SET SESSION AUTOCOMMIT=1"));
-				break;
 			case 'oci':
 				$eventManager->addEventSubscriber(new OracleSessionInit);
 				// the driverOptions are unused in dbal and need to be mapped to the parameters
@@ -159,7 +155,7 @@ public function getConnection($type, $additionalConnectionParams) {
 		}
 		/** @var Connection $connection */
 		$connection = DriverManager::getConnection(
-			array_merge($this->getDefaultConnectionParams($type), $additionalConnectionParams),
+			$additionalConnectionParams,
 			new Configuration(),
 			$eventManager
 		);
@@ -195,10 +191,10 @@ public function isValidType($type) {
 	public function createConnectionParams(string $configPrefix = '') {
 		$type = $this->config->getValue('dbtype', 'sqlite');
 
-		$connectionParams = [
+		$connectionParams = array_merge($this->getDefaultConnectionParams($type), [
 			'user' => $this->config->getValue($configPrefix . 'dbuser', $this->config->getValue('dbuser', '')),
 			'password' => $this->config->getValue($configPrefix . 'dbpassword', $this->config->getValue('dbpassword', '')),
-		];
+		]);
 		$name = $this->config->getValue($configPrefix . 'dbname', $this->config->getValue('dbname', self::DEFAULT_DBNAME));
 
 		if ($this->normalizeType($type) === 'sqlite3') {
@@ -237,7 +233,11 @@ public function createConnectionParams(string $configPrefix = '') {
 			$connectionParams['persistent'] = true;
 		}
 
-		return $connectionParams;
+		$replica = $this->config->getValue('dbreplica', []) ?: [$connectionParams];
+		return array_merge($connectionParams, [
+			'primary' => $connectionParams,
+			'replica' => $replica,
+		]);
 	}
 
 	/**

lib/private/DB/SetTransactionIsolationLevel.php

@@ -26,8 +26,10 @@
 namespace OC\DB;
 
 use Doctrine\Common\EventSubscriber;
+use Doctrine\DBAL\Connections\PrimaryReadReplicaConnection;
 use Doctrine\DBAL\Event\ConnectionEventArgs;
 use Doctrine\DBAL\Events;
+use Doctrine\DBAL\Platforms\MySQLPlatform;
 use Doctrine\DBAL\TransactionIsolationLevel;
 
 class SetTransactionIsolationLevel implements EventSubscriber {
@@ -36,7 +38,13 @@ class SetTransactionIsolationLevel implements EventSubscriber {
 	 * @return void
 	 */
 	public function postConnect(ConnectionEventArgs $args) {
-		$args->getConnection()->setTransactionIsolation(TransactionIsolationLevel::READ_COMMITTED);
+		$connection = $args->getConnection();
+		if ($connection instanceof PrimaryReadReplicaConnection && $connection->isConnectedToPrimary()) {
+			$connection->setTransactionIsolation(TransactionIsolationLevel::READ_COMMITTED);
+			if ($connection->getDatabasePlatform() instanceof MySQLPlatform) {
+				$connection->executeStatement('SET SESSION AUTOCOMMIT=1');
+			}
+		}
 	}
 
 	public function getSubscribedEvents() {

lib/private/Server.php

@@ -842,8 +842,7 @@ public function __construct($webRoot, \OC\Config $config) {
 			if (!$factory->isValidType($type)) {
 				throw new \OC\DatabaseException('Invalid database type');
 			}
-			$connectionParams = $factory->createConnectionParams();
-			$connection = $factory->getConnection($type, $connectionParams);
+			$connection = $factory->getConnection($type, []);
 			return $connection;
 		});
 		/** @deprecated 19.0.0 */

lib/private/Setup/AbstractDatabase.php

@@ -141,7 +141,7 @@ protected function connect(array $configOverwrite = []): Connection {
 			$connectionParams['host'] = $host;
 		}
 
-		$connectionParams = array_merge($connectionParams, $configOverwrite);
+		$connectionParams = array_merge($connectionParams, ['primary' => $connectionParams, 'replica' => [$connectionParams]], $configOverwrite);
 		$cf = new ConnectionFactory($this->config);
 		return $cf->getConnection($this->config->getValue('dbtype', 'sqlite'), $connectionParams);
 	}