diff --git a/appinfo/info.xml b/appinfo/info.xml
index a4c4bba7..f7a30a64 100644
--- a/appinfo/info.xml
+++ b/appinfo/info.xml
@@ -34,6 +34,12 @@ Core App of the full-text search framework for your Nextcloud.
 		<job>OCA\FullTextSearch\Cron\Index</job>
 	</background-jobs>
 
+	<repair-steps>
+		<install>
+			<step>OCA\FullTextSearch\RepairStep\AppEnabled</step>
+		</install>
+	</repair-steps>
+
 	<commands>
 		<command>OCA\FullTextSearch\Command\Check</command>
 		<command>OCA\FullTextSearch\Command\CollectionInit</command>
@@ -50,6 +56,7 @@ Core App of the full-text search framework for your Nextcloud.
 		<command>OCA\FullTextSearch\Command\Reset</command>
 		<command>OCA\FullTextSearch\Command\Search</command>
 		<command>OCA\FullTextSearch\Command\Stop</command>
+		<command>OCA\FullTextSearch\Command\Sync</command>
 		<command>OCA\FullTextSearch\Command\Test</command>
 	</commands>
 
diff --git a/lib/AppInfo/Application.php b/lib/AppInfo/Application.php
index b5994b91..23792fd6 100644
--- a/lib/AppInfo/Application.php
+++ b/lib/AppInfo/Application.php
@@ -11,10 +11,14 @@
 
 
 use Closure;
+use NCU\FullTextSearch\IManager;
 use OC;
+use OC\FullTextSearch\FullTextSearchManager;
 use OCA\FullTextSearch\Capabilities;
 use OCA\FullTextSearch\ConfigLexicon;
+use OCA\FullTextSearch\Provider\FilesContentProvider;
 use OCA\FullTextSearch\Search\UnifiedSearchProvider;
+use OCA\FullTextSearch\Service\FullTextSearchService;
 use OCA\FullTextSearch\Service\IndexService;
 use OCA\FullTextSearch\Service\ProviderService;
 use OCA\FullTextSearch\Service\SearchService;
@@ -41,6 +45,9 @@ public function register(IRegistrationContext $context): void {
 		$context->registerCapability(Capabilities::class);
 		$context->registerSearchProvider(UnifiedSearchProvider::class);
 		$context->registerConfigLexicon(ConfigLexicon::class);
+
+		$context->registerFullTextSearchService(FullTextSearchService::class);
+
 		$this->registerServices($this->getContainer());
 	}
 
@@ -53,11 +60,8 @@ public function boot(IBootContext $context): void {
 		$context->injectFn(Closure::fromCallable([$this, 'registerNavigation']));
 	}
 
-
 	/**
-	 * Register Navigation Tab
-	 *
-	 * @param ContainerInterface $container
+	 * @deprecated
 	 */
 	protected function registerServices(ContainerInterface $container) {
 		/** @var IFullTextSearchManager $fullTextSearchManager */
diff --git a/lib/Command/Stop.php b/lib/Command/Stop.php
index 6d9e545b..d016219f 100644
--- a/lib/Command/Stop.php
+++ b/lib/Command/Stop.php
@@ -41,7 +41,7 @@ protected function configure() {
 	protected function execute(InputInterface $input, OutputInterface $output) {
 		$output->writeln('stopping all running indexes');
 
-		$this->runningService->forceStop();
+		$this->runningService->stop();
 
 		return 0;
 	}
diff --git a/lib/Command/Sync.php b/lib/Command/Sync.php
new file mode 100644
index 00000000..d081c401
--- /dev/null
+++ b/lib/Command/Sync.php
@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2016 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Command;
+
+use OC\Core\Command\Base;
+use OCA\FullTextSearch\Exceptions\PlatformTemporaryException;
+use OCA\FullTextSearch\Service\FullTextSearchService;
+use OCA\FullTextSearch\Service\LockService;
+use OCA\FullTextSearch\Service\LoggerService;
+use OCA\FullTextSearch\Service\SyncService;
+use OCA\FullTextSearch\Tools\Traits\TArrayTools;
+use Exception;
+use OC\Core\Command\InterruptedException;
+use OCA\FullTextSearch\ACommandBase;
+use OCA\FullTextSearch\Exceptions\TickDoesNotExistException;
+use OCA\FullTextSearch\Model\Index as ModelIndex;
+use OCA\FullTextSearch\Model\Runner;
+use OCA\FullTextSearch\Service\CliService;
+use OCA\FullTextSearch\Service\ConfigService;
+use OCA\FullTextSearch\Service\IndexService;
+use OCA\FullTextSearch\Service\PlatformService;
+use OCA\FullTextSearch\Service\ProviderService;
+use OCA\FullTextSearch\Service\RunningService;
+use OCP\IUserManager;
+use OutOfBoundsException;
+use Psr\Log\LoggerInterface;
+use Symfony\Component\Console\Formatter\OutputFormatterStyle;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Console\Terminal;
+use Throwable;
+
+class Sync extends Base {
+	public function __construct(
+		private readonly LockService $lockService,
+		private readonly SyncService $syncService,
+		private readonly FullTextSearchService $fullTextSearchService,
+		private readonly LoggerService $loggerService,
+	) {
+		parent::__construct();
+	}
+
+	protected function configure() {
+		parent::configure();
+		$this->setName('fulltextsearch:sync')
+			 ->setDescription('Index files')
+			->addOption('info', '', InputOption::VALUE_NONE, 'display info entries')
+			 ->addOption('no-output', '', InputOption::VALUE_NONE, 'no output, use nextcloud logs');
+	}
+
+	protected function execute(InputInterface $input, OutputInterface $output) {
+		if (!$input->getOption('no-output')) {
+			$this->loggerService->setOutputInterface($output, $input->getOption('info'));
+		}
+//		$this->fullTextSearchService->requestIndex('files', '123');
+		$this->lockService->lock();
+
+		while (true) {
+			try {
+				$this->lockService->update();
+				$this->syncProcess();
+			} catch (Exception $e) {
+				$this->loggerService->error('Exception while running fulltextsearch:sync', ['exception' => $e]);
+			}
+			sleep(10);
+		}
+
+		return 0;
+	}
+
+	private function syncProcess() {
+		$this->loggerService->info('initiating a new sync session');
+		$this->syncService->smartSync();
+		$this->loggerService->info('sync session closed');
+	}
+}
+
diff --git a/lib/ConfigLexicon.php b/lib/ConfigLexicon.php
index df348e06..ca119f7a 100644
--- a/lib/ConfigLexicon.php
+++ b/lib/ConfigLexicon.php
@@ -26,8 +26,10 @@ class ConfigLexicon implements ILexicon {
 	public const COLLECTION_INDEXING_LIST = 'collection_indexing_list';
 	public const COLLECTION_INTERNAL = 'collection_internal';
 	public const COLLECTION_LINKS = 'collection_links';
+	public const SYNC_REQUIREMENT_LEVEL = 'sync_requirement';
 	public const LOCK_ID = 'lock_id';
 	public const LOCK_PING = 'lock_ping';
+	public const ENABLED_SINCE = 'enabled_since';
 
 	public function getStrictness(): Strictness {
 		return Strictness::NOTICE;
@@ -42,9 +44,10 @@ public function getAppConfigs(): array {
 			new Entry(key: self::COLLECTION_INDEXING_LIST, type: ValueType::INT, defaultRaw: 50, definition: 'size of chunks of async documents on collection queue request'),
 			new Entry(key: self::COLLECTION_INTERNAL, type: ValueType::STRING, defaultRaw: 'local', definition: 'name of the local collection'),
 			new Entry(key: self::COLLECTION_LINKS, type: ValueType::ARRAY, defaultRaw: [], definition: '(internal) data relative to collections'),
-			// IAppConfig::FLAG_INTERNAL)
-			new Entry(key: self::LOCK_ID, type: ValueType::STRING, defaultRaw: '', definition: 'internal lock id', lazy: true),
-			new Entry(key: self::LOCK_PING, type: ValueType::INT, defaultRaw: 0, definition: 'internal lock time', lazy: true),
+			new Entry(key: self::SYNC_REQUIREMENT_LEVEL, type: ValueType::INT, defaultRaw: 0, definition: 'requirement level to confirm the need for sync'),
+			new Entry(key: self::LOCK_ID, type: ValueType::STRING, defaultRaw: '', definition: 'internal lock id', lazy: true, flags: IAppConfig::FLAG_INTERNAL),
+			new Entry(key: self::LOCK_PING, type: ValueType::INT, defaultRaw: 0, definition: 'internal lock time', lazy: true, flags: IAppConfig::FLAG_INTERNAL),
+			new Entry(key: self::ENABLED_SINCE, type: ValueType::INT, defaultRaw: 0, definition: 'the time since the fulltextsearch app is enabled', lazy: true, flags: IAppConfig::FLAG_INTERNAL),
 		];
 	}
 
diff --git a/lib/Db/SyncMapper.php b/lib/Db/SyncMapper.php
new file mode 100644
index 00000000..4ad25095
--- /dev/null
+++ b/lib/Db/SyncMapper.php
@@ -0,0 +1,64 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Db;
+
+use OCA\FullTextSearch\Model\DocumentSync;
+use OCP\AppFramework\Db\Entity;
+use OCP\AppFramework\Db\QBMapper;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+
+/**
+ * @template-extends QBMapper<DocumentSync>
+ */
+class SyncMapper extends QBMapper {
+	public const TABLE = 'fulltextsearch_sync';
+
+	public function __construct(
+		IDBConnection $db,
+	) {
+		parent::__construct($db, self::TABLE, DocumentSync::class);
+	}
+
+	/**
+	 * @return DocumentSync[]
+	 */
+	public function getForcedSyncs(int $limit = 100): array {
+		$qb = $this->db->getQueryBuilder();
+		$qb->select('*')
+		   ->from($this->getTableName())
+		   ->where($qb->expr()->eq('indexed', $qb->createNamedParameter(0, IQueryBuilder::PARAM_INT)))
+		   ->setMaxResults($limit);
+
+		return $this->findEntities($qb);
+	}
+
+	public function update(Entity $entity): Entity {
+		$qb = $this->db->getQueryBuilder();
+		$qb->update($this->getTableName())
+			->set('indexed', $qb->createNamedParameter($entity->getIndexed(), IQueryBuilder::PARAM_INT))
+			->where(
+				$qb->expr()->eq('provider_id', $qb->createNamedParameter($entity->getProviderId())),
+				$qb->expr()->eq('document_id', $qb->createNamedParameter($entity->getDocumentId())),
+			);
+		$qb->executeStatement();
+		return $entity;
+	}
+
+//	public function reset(string $providerId, string $documentId): void {
+//		$qb = $this->db->getQueryBuilder();
+//		$qb->update($this->getTableName())
+//		   ->set('indexed', $qb->createNamedParameter(0, IQueryBuilder::PARAM_INT))
+//		   ->where(
+//			   $qb->expr()->eq('provider_id', $qb->createNamedParameter($providerId())),
+//			   $qb->expr()->eq('document_id', $qb->createNamedParameter($documentId())),
+//		   );
+//		$qb->executeStatement();
+//	}
+}
diff --git a/lib/Enum/SessionType.php b/lib/Enum/SessionType.php
new file mode 100644
index 00000000..b43f7ec0
--- /dev/null
+++ b/lib/Enum/SessionType.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Enum;
+
+enum SessionType: string {
+	case UNKNOWN = '';
+	case FORCED = 'forced';
+	case SYNC = 'sync';
+	case RESYNC = 'sync_recent';
+}
diff --git a/lib/Migration/Version23001Date20220408140253.php b/lib/Migration/Version23001Date20220408140253.php
index 0df72c94..7099fb97 100644
--- a/lib/Migration/Version23001Date20220408140253.php
+++ b/lib/Migration/Version23001Date20220408140253.php
@@ -28,11 +28,11 @@ public function changeSchema(IOutput $output, Closure $schemaClosure, array $opt
 		/** @var ISchemaWrapper $schema */
 		$schema = $schemaClosure();
 
-		if (!$schema->hasTable('fulltextsearch_indexes')) {
+		if (!$schema->hasTable('fulltextsearch_sync')) {
 			return null;
 		}
 
-		$table = $schema->getTable('fulltextsearch_indexes');
+		$table = $schema->getTable('fulltextsearch_sync');
 		$column = $table->getColumn('message');
 
 		if ($column->getType()->getName() === Types::TEXT) {
diff --git a/lib/Migration/Version33001Date202511271645.php b/lib/Migration/Version33001Date202511271645.php
new file mode 100644
index 00000000..098eb7c5
--- /dev/null
+++ b/lib/Migration/Version33001Date202511271645.php
@@ -0,0 +1,55 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Migration;
+
+use Closure;
+use OCP\DB\ISchemaWrapper;
+use OCP\DB\Types;
+use OCP\Migration\Attributes\CreateTable;
+use OCP\Migration\IOutput;
+use OCP\Migration\SimpleMigrationStep;
+
+#[CreateTable('fulltextsearch_sync', ['provider_id', 'document_id', 'indexed'], description: 'table to manage indexed documents and new index request')]
+class Version33001Date202511271645 extends SimpleMigrationStep {
+	public function changeSchema(IOutput $output, Closure $schemaClosure, array $options): ?ISchemaWrapper {
+		/** @var ISchemaWrapper $schema */
+		$schema = $schemaClosure();
+		if ($schema->hasTable('fulltextsearch_sync')) {
+			return null;
+		}
+
+		$table = $schema->createTable('fulltextsearch_sync');
+		$table->addColumn('provider_id', Types::STRING, [
+			'length' => 31,
+			'notnull' => true,
+		]);
+		$table->addColumn('document_id', Types::STRING, [
+			'length' => 31,
+			'notnull' => true,
+		]);
+		$table->addColumn('flags', Types::INTEGER, [
+			'length' => 7,
+			'default' => 0,
+		]);
+		$table->addColumn('indexed', Types::BIGINT, [
+			'length' => 11,
+			'default' => 0,
+		]);
+		$table->addColumn('checksum', Types::STRING, [
+			'length' => 16,
+			'notnull' => true,
+		]);
+
+		$table->setPrimaryKey(['provider_id', 'document_id'], 'fts_i_pd');
+		$table->addIndex(['indexed'], 'fts_i_i');
+
+		return $schema;
+	}
+}
diff --git a/lib/Model/DocumentSync.php b/lib/Model/DocumentSync.php
new file mode 100644
index 00000000..67de7f5d
--- /dev/null
+++ b/lib/Model/DocumentSync.php
@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\FullTextSearch\Model;
+
+use OCP\AppFramework\Db\Entity;
+
+/**
+ * @method void setProviderId(string $providerId)
+ * @method string getProviderId()
+ * @method void setDocumentId(string $documentId)
+ * @method string getDocumentId()
+ * @method void setFlags(int $indexed)
+ * @method int getFlags()
+ * @method void setIndexed(int $indexed)
+ * @method int getIndexed()
+ * @method void setChecksum(string $checksum)
+ * @method string getChecksum()
+ * @psalm-suppress PropertyNotSetInConstructor
+ */
+class DocumentSync extends Entity {
+	protected string $providerId = '';
+	protected string $documentId = '';
+	protected int $flags = 0;
+	protected int $indexed = 0;
+	protected string $checksum = '';
+
+	public function __construct(
+	) {
+		$this->addType('providerId', 'string');
+		$this->addType('documentId', 'string');
+		$this->addType('flags', 'integer');
+		$this->addType('indexed', 'integer');
+		$this->addType('checksum', 'string');
+	}
+
+	public function definition(): string {
+		return $this->getProviderId() . '/' . $this->getDocumentId();
+	}
+}
diff --git a/lib/Model/IndexQueryHelper.php b/lib/Model/IndexQueryHelper.php
new file mode 100644
index 00000000..f9f9e9df
--- /dev/null
+++ b/lib/Model/IndexQueryHelper.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2023 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Model;
+
+use NCU\FullTextSearch\IIndexQueryHelper;
+
+class IndexQueryHelper implements IIndexQueryHelper {
+	private bool $needed = true;
+
+	public function __construct() {
+	}
+
+	public function notNeeded(): void {
+		$this->needed = false;
+	}
+
+	public function isNeeded(): bool {
+		return $this->needed;
+	}
+}
diff --git a/lib/RepairStep/AppEnabled.php b/lib/RepairStep/AppEnabled.php
new file mode 100644
index 00000000..85f74c9e
--- /dev/null
+++ b/lib/RepairStep/AppEnabled.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\RepairStep;
+
+use OCA\FullTextSearch\AppInfo\Application;
+use OCA\FullTextSearch\ConfigLexicon;
+use OCP\IAppConfig;
+use OCP\Migration\IOutput;
+use OCP\Migration\IRepairStep;
+
+class AppEnabled implements IRepairStep {
+	public function __construct(
+		private readonly IAppConfig $appConfig,
+	) {
+	}
+
+	public function getName() {
+		return 'prep re-sync';
+	}
+
+	public function run(IOutput $output) {
+		$this->appConfig->setValueInt(Application::APP_ID, ConfigLexicon::ENABLED_SINCE, time());
+	}
+}
diff --git a/lib/Service/FullTextSearchService.php b/lib/Service/FullTextSearchService.php
new file mode 100644
index 00000000..eb49b169
--- /dev/null
+++ b/lib/Service/FullTextSearchService.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Service;
+
+use NCU\FullTextSearch\IService;
+use OCA\FullTextSearch\Db\SyncMapper;
+use OCA\FullTextSearch\Model\DocumentSync;
+use NCU\FullTextSearch\ILoggerService;
+use OCP\DB\Exception;
+use Psr\Log\LoggerInterface;
+
+class FullTextSearchService implements IService {
+	public function __construct(
+		private readonly SyncMapper $mapper,
+		private readonly LoggerInterface $logger,
+		private readonly LoggerService $loggerService,
+	) {
+	}
+
+	public function getLogger(): ILoggerService {
+		return $this->loggerService;
+	}
+
+	public function requestIndex(string $providerId, string $documentId): void {
+		$index = new DocumentSync();
+		$index->setProviderId($providerId);
+		$index->setDocumentId($documentId);
+		$index->setIndexed(0);
+		$index->setChecksum('');
+
+		try {
+			$this->mapper->insertOrUpdate($index);
+		} catch (Exception $e) {
+			$this->logger->warning('could not store index', ['exception' => $e]);
+		}
+	}
+
+	public function deleteIndex(string $providerId, string $documentId): void {
+	}
+}
diff --git a/lib/Service/LoggerService.php b/lib/Service/LoggerService.php
new file mode 100644
index 00000000..5a02d894
--- /dev/null
+++ b/lib/Service/LoggerService.php
@@ -0,0 +1,72 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2017 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Service;
+
+use NCU\FullTextSearch\ILoggerService;
+use OCA\FullTextSearch\Enum\SessionType;
+use Psr\Log\LoggerInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+class LoggerService implements ILoggerService {
+	private ?OutputInterface $output = null;
+	private bool $verbose = false;
+	private SessionType $currentSessionType = SessionType::UNKNOWN;
+
+	public function __construct(
+		private ?LoggerInterface $logger,
+		private readonly LoggerInterface $loggerError,
+	) {
+	}
+
+	/**
+	 * override debug in nextcloud log with an output interface
+	 */
+	public function setOutputInterface(OutputInterface $output, bool $verbose = false): void {
+		$this->verbose = $verbose;
+		$this->output = $output;
+		$this->logger = null;
+	}
+
+	public function info(string $entry): void {
+		if ($this->verbose) {
+			$this->output?->writeln($this->prepOutput() . ' ' . $this->prepEntry($entry, 'comment'));
+		}
+		$this->logger?->debug('[' . $this->currentSessionType->value . '] ' . 'info: ' . $entry);
+	}
+
+	public function action(string $entry): void {
+		$this->output?->writeln($this->prepOutput() . ' ' . $this->prepEntry($entry));
+		$this->logger?->debug('[' . $this->currentSessionType->value . '] ' . 'action: ' . $entry);
+	}
+
+	public function warning(string $entry, array $data = []): void {
+		$this->output?->writeln($this->prepOutput() . ' ' . $this->prepEntry($entry, 'error'));
+		$this->logger?->warning('[' . $this->currentSessionType->value . '] ' . $entry, $data);
+	}
+
+	public function error(string $entry, array $data = []): void {
+		$this->output?->writeln($this->prepOutput() . ' ' . $this->prepEntry($entry, 'error'));
+		$this->loggerError->warning('[' . $this->currentSessionType->value . '] ' . $entry, $data);
+	}
+
+	public function session(SessionType $sessionType = SessionType::UNKNOWN): void {
+		$this->currentSessionType = $sessionType;
+	}
+
+	private function prepOutput(): string {
+		return '<fg=gray>' . date('[H:i:s]') . '</> ';
+	}
+
+	private function prepEntry(string $entry, string $tag = ''): string {
+		$entry = ($tag !== '') ? '<' . $tag . '>' . $entry . '</>' : $entry;
+		$prefix = '<fg=gray>(' . str_pad($this->currentSessionType->value . ')', 14, ' ') . '</>';
+		return $prefix . $entry;
+	}
+}
diff --git a/lib/Service/ProcessService.php b/lib/Service/ProcessService.php
new file mode 100644
index 00000000..5d2cc5cc
--- /dev/null
+++ b/lib/Service/ProcessService.php
@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Service;
+
+use OCA\FullTextSearch\Model\DocumentSync;
+use OCP\IDBConnection;
+
+class ProcessService {
+	private int $forkCount = 0;
+	private const FORK_LIMIT = 8; // maximum number of child process
+	private const FORK_SLEEP = 500000; // wait for msec when too many fork have been created
+	public function __construct(
+		private readonly IDBConnection $connection,
+	) {
+	}
+
+	public function forkIndexDocument(DocumentSync $sync, callable $indexDocument): void {
+		if (!extension_loaded('posix')) {
+			$indexDocument($sync);
+			return;
+		}
+
+		$pid = pcntl_fork();
+
+		// work around as the parent database connection is inherited by the child.
+		// when child process is over, parent process database connection will drop.
+		// The drop can happen anytime, even in the middle of a running request.
+		// work around is to close the connection as soon as possible after forking.
+		$this->connection->close();
+
+		if ($pid === -1) {
+			// TODO: manage issue while forking
+		} else if ($pid === 0) {
+			// forked process
+			$indexDocument($sync);
+			exit();
+		} else {
+			// main process, counting forks
+			$this->forkCount++;
+			while (true) {
+				if (pcntl_waitpid(0, $status, WNOHANG) !== 0) {
+					$this->forkCount--;
+				}
+				if ($this->forkCount < self::FORK_LIMIT) {
+					return;
+				}
+				usleep(self::FORK_SLEEP);
+			}
+		}
+	}
+
+	public function waitForChild(): void {
+		if (!extension_loaded('posix')) {
+			return;
+		}
+
+		while (pcntl_waitpid(0, $status) !== -1) {
+		}
+	}
+}
diff --git a/lib/Service/ProviderService.php b/lib/Service/ProviderService.php
index 6e2251e2..6142736b 100644
--- a/lib/Service/ProviderService.php
+++ b/lib/Service/ProviderService.php
@@ -269,5 +269,4 @@ public function addJavascriptAPI() {
 		Util::addScript(Application::APP_ID, 'fulltextsearch.v1');
 	}
 
-
 }
diff --git a/lib/Service/RunningService.php b/lib/Service/RunningService.php
index 8337d657..bacb0baa 100644
--- a/lib/Service/RunningService.php
+++ b/lib/Service/RunningService.php
@@ -25,7 +25,7 @@ public function __construct(
 	/**
 	 * @deprecated
 	 */
-	public function start(string $source): int {
+	public function start(string $source = ''): int {
 		try {
 			$this->lockService->lock();
 		} catch (LockException $e) {
@@ -37,7 +37,7 @@ public function start(string $source): int {
 	/**
 	 * @deprecated
 	 */
-	public function update(int $runId, string $action = '') {
+	public function update(int $runId = 0, string $action = '') {
 		try {
 			$this->lockService->update();
 		} catch (LockException $e) {
@@ -48,7 +48,7 @@ public function update(int $runId, string $action = '') {
 	/**
 	 * @deprecated
 	 */
-	public function stop(int $runId, string $reason = '') {
+	public function stop(int $runId = 0, string $reason = '') {
 		$this->lockService->unlock();
 	}
 }
diff --git a/lib/Service/SyncService.php b/lib/Service/SyncService.php
new file mode 100644
index 00000000..41dd5375
--- /dev/null
+++ b/lib/Service/SyncService.php
@@ -0,0 +1,170 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\FullTextSearch\Service;
+
+use NCU\FullTextSearch\IManager as IFullTextSearchManager;
+use OCA\FullTextSearch\ConfigLexicon;
+use OCA\FullTextSearch\Db\SyncMapper;
+use OCA\FullTextSearch\Enum\SessionType;
+use OCA\FullTextSearch\Model\DocumentSync;
+use NCU\FullTextSearch\IContentProvider;
+use OCP\AppFramework\Services\IAppConfig;
+use OCP\Server;
+use Psr\Container\ContainerExceptionInterface;
+use Psr\Container\NotFoundExceptionInterface;
+use Psr\Log\LoggerInterface;
+
+class SyncService {
+	public const SYNC_LEVEL_NONE = 0;
+	public const SYNC_LEVEL_CHECKSUM = 3;
+
+
+	public function __construct(
+		private readonly IAppConfig $appConfig,
+		private readonly IFullTextSearchManager $manager,
+		private readonly SyncMapper $mapper,
+		private readonly ProcessService $processService,
+		private readonly ProviderService $providerService,
+		private readonly LoggerService $logger,
+		private readonly LoggerInterface $coreLogger,
+	) {
+	}
+
+	/**
+	 * initiate one sync session from the list below and returns TRUE
+	 * if a sync session did not index any document, the next entry from the list is initiated
+	 * once all entries are done, method returns FALSE
+	 *
+	 * - sync forced index (indexed=0),
+	 * - sync provider using IFTSSyncIndex,
+	 * - sync document indexed previously to enabled_since and less than 10 times the time between NOW and ENABLED_SINCE
+	 * - sync document indexed previously to enabled_since and more than 6 months ago,
+	 * - sync document indexed previously to enabled_since and more than 3 months ago,
+	 * - sync document indexed previously to enabled_since and more than 4 weeks ago,
+	 * - sync document indexed previously to enabled_since and more than 2 weeks ago,
+	 * - sync document indexed previously to enabled_since and more than 1 weeks ago,
+	 * - sync document indexed previously to enabled_since.
+	 */
+	public function smartSync(): bool {
+		// TODO: test link with ES
+		return ($this->syncForcedIndexes()
+				|| $this->syncContentProviders()
+				|| $this->resyncRecentDocuments()
+				|| $this->syncOlderDocuments(6 * 30 * 24 * 3600)
+				|| $this->syncOlderDocuments(3 * 30 * 24 * 3600)
+				|| $this->syncOlderDocuments(4 * 7 * 24 * 3600)
+				|| $this->syncOlderDocuments(2 * 7 * 24 * 3600)
+				|| $this->syncOlderDocuments(7 * 24 * 3600)
+				|| $this->syncOlderDocuments()
+		);
+	}
+
+	/**
+	 * index documents that have been set as out-of-sync
+	 *
+	 * @return bool FALSE if no out-of-sync documents were found
+	 */
+	public function syncForcedIndexes(int $limit = 100): bool {
+		$this->logger->session(SessionType::FORCED);
+		$syncDocuments = $this->mapper->getForcedSyncs($limit);
+		if (empty($syncDocuments)) {
+			return false;
+		}
+		$this->syncDocuments($syncDocuments);
+		return true;
+	}
+
+	/**
+	 * request provider for possible unknown documents to be indexed
+	 *
+	 * @return bool FALSE if none were found
+	 */
+	public function syncContentProviders(): bool {
+		$this->logger->session(SessionType::SYNC);
+		foreach ($this->manager->getContentProviders() as $provider) {
+			$this->syncContentProvider($provider);
+		}
+
+		return false;
+	}
+
+	public function syncContentProvider(string $providerId): void {
+		//$this->logger->action('providerId: ' . $providerId);
+	}
+
+	private function resyncRecentDocuments(): bool {
+		$this->logger->session(SessionType::FORCED);
+		return false;
+	}
+
+	private function syncOlderDocuments($olderThan = 0): bool {
+		return false;
+	}
+
+	public function syncDocuments(array $syncDocuments): void {
+		foreach ($syncDocuments as $sync) {
+			$this->processService->forkIndexDocument($sync, [$this, 'syncDocument']);
+		}
+		$this->processService->waitForChild();
+	}
+
+	public function syncDocument(DocumentSync $sync): void {
+		$time = time();
+		$this->logger->action('indexing document ' . $sync->definition());
+		$this->indexDocument($sync);
+		$sync->setIndexed($time);
+
+//		$this->mapper->insertOrUpdate($sync);
+	}
+
+	private function indexDocument(DocumentSync $sync): void {
+		$provider = $this->getContentProvider($sync->getProviderId());
+		if ($provider === null) {
+			$this->logger->error('provider ' . $sync->getProviderId() . ' not found');
+			return;
+		}
+
+		$document = $provider->getDocument($sync->getDocumentId());
+		if ($document === null) {
+			$this->logger->info('document ' . $sync->definition() . ' not found');
+			return;
+		}
+
+		$checksum = $document->getChecksum();
+		if (($sync->getChecksum() === $checksum) && ($this->appConfig->getAppValueString(ConfigLexicon::SYNC_REQUIREMENT_LEVEL) >= self::SYNC_LEVEL_CHECKSUM)) {
+			$this->logger->logger('document ' . $sync->definition() . ' seems to be identical to the indexed version');
+			return;
+		}
+
+		$sync->setChecksum($checksum);
+
+		echo json_encode($document->getFlags()) . '  ' . json_encode($document->getContent()) . "\n";
+		// get document
+		// send document to ES
+		// confirm it is done
+		sleep(rand(1, 15));
+	}
+
+	private function getContentProvider(string $providerId): ?IContentProvider {
+		foreach ($this->manager->getContentProviders() as $providerClass) {
+			try {
+				$provider = Server::get($providerClass);
+				if ($provider->getId() === $providerId) {
+					return $provider;
+				}
+			} catch (NotFoundExceptionInterface|ContainerExceptionInterface $e) {
+				$this->coreLogger->warning('could not load ' . $providerClass, ['exception' => $e]);
+			}
+		}
+
+		return null;
+	}
+
+}