feat: implement distributing partitioned queries over multiple shards

Signed-off-by: Robin Appelman <robin@icewind.nl>

lib/composer/composer/autoload_classmap.php

@@ -247,6 +247,7 @@ return array(
     'OCP\\DB\\QueryBuilder\\IParameter' => $baseDir . '/lib/public/DB/QueryBuilder/IParameter.php',
     'OCP\\DB\\QueryBuilder\\IQueryBuilder' => $baseDir . '/lib/public/DB/QueryBuilder/IQueryBuilder.php',
     'OCP\\DB\\QueryBuilder\\IQueryFunction' => $baseDir . '/lib/public/DB/QueryBuilder/IQueryFunction.php',
+    'OCP\\DB\\QueryBuilder\\Sharded\\IShardMapper' => $baseDir . '/lib/public/DB/QueryBuilder/Sharded/IShardMapper.php',
     'OCP\\DB\\Types' => $baseDir . '/lib/public/DB/Types.php',
     'OCP\\Dashboard\\IAPIWidget' => $baseDir . '/lib/public/Dashboard/IAPIWidget.php',
     'OCP\\Dashboard\\IAPIWidgetV2' => $baseDir . '/lib/public/Dashboard/IAPIWidgetV2.php',
@@ -1418,6 +1419,15 @@ return array(
     'OC\\DB\\QueryBuilder\\QueryBuilder' => $baseDir . '/lib/private/DB/QueryBuilder/QueryBuilder.php',
     'OC\\DB\\QueryBuilder\\QueryFunction' => $baseDir . '/lib/private/DB/QueryBuilder/QueryFunction.php',
     'OC\\DB\\QueryBuilder\\QuoteHelper' => $baseDir . '/lib/private/DB/QueryBuilder/QuoteHelper.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\AutoIncrementHandler' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/AutoIncrementHandler.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\CrossShardMoveHelper' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/CrossShardMoveHelper.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\HashShardMapper' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/HashShardMapper.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\InvalidShardedQueryException' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/InvalidShardedQueryException.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\RoundRobinShardMapper' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/RoundRobinShardMapper.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\ShardConnectionManager' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/ShardConnectionManager.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\ShardDefinition' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/ShardDefinition.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\ShardQueryRunner' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/ShardQueryRunner.php',
+    'OC\\DB\\QueryBuilder\\Sharded\\ShardedQueryBuilder' => $baseDir . '/lib/private/DB/QueryBuilder/Sharded/ShardedQueryBuilder.php',
     'OC\\DB\\ResultAdapter' => $baseDir . '/lib/private/DB/ResultAdapter.php',
     'OC\\DB\\SQLiteMigrator' => $baseDir . '/lib/private/DB/SQLiteMigrator.php',
     'OC\\DB\\SQLiteSessionInit' => $baseDir . '/lib/private/DB/SQLiteSessionInit.php',

lib/composer/composer/autoload_static.php

@@ -280,6 +280,7 @@ class ComposerStaticInit749170dad3f5e7f9ca158f5a9f04f6a2
         'OCP\\DB\\QueryBuilder\\IParameter' => __DIR__ . '/../../..' . '/lib/public/DB/QueryBuilder/IParameter.php',
         'OCP\\DB\\QueryBuilder\\IQueryBuilder' => __DIR__ . '/../../..' . '/lib/public/DB/QueryBuilder/IQueryBuilder.php',
         'OCP\\DB\\QueryBuilder\\IQueryFunction' => __DIR__ . '/../../..' . '/lib/public/DB/QueryBuilder/IQueryFunction.php',
+        'OCP\\DB\\QueryBuilder\\Sharded\\IShardMapper' => __DIR__ . '/../../..' . '/lib/public/DB/QueryBuilder/Sharded/IShardMapper.php',
         'OCP\\DB\\Types' => __DIR__ . '/../../..' . '/lib/public/DB/Types.php',
         'OCP\\Dashboard\\IAPIWidget' => __DIR__ . '/../../..' . '/lib/public/Dashboard/IAPIWidget.php',
         'OCP\\Dashboard\\IAPIWidgetV2' => __DIR__ . '/../../..' . '/lib/public/Dashboard/IAPIWidgetV2.php',
@@ -1451,6 +1452,15 @@ class ComposerStaticInit749170dad3f5e7f9ca158f5a9f04f6a2
         'OC\\DB\\QueryBuilder\\QueryBuilder' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/QueryBuilder.php',
         'OC\\DB\\QueryBuilder\\QueryFunction' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/QueryFunction.php',
         'OC\\DB\\QueryBuilder\\QuoteHelper' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/QuoteHelper.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\AutoIncrementHandler' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/AutoIncrementHandler.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\CrossShardMoveHelper' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/CrossShardMoveHelper.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\HashShardMapper' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/HashShardMapper.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\InvalidShardedQueryException' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/InvalidShardedQueryException.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\RoundRobinShardMapper' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/RoundRobinShardMapper.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\ShardConnectionManager' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/ShardConnectionManager.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\ShardDefinition' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/ShardDefinition.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\ShardQueryRunner' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/ShardQueryRunner.php',
+        'OC\\DB\\QueryBuilder\\Sharded\\ShardedQueryBuilder' => __DIR__ . '/../../..' . '/lib/private/DB/QueryBuilder/Sharded/ShardedQueryBuilder.php',
         'OC\\DB\\ResultAdapter' => __DIR__ . '/../../..' . '/lib/private/DB/ResultAdapter.php',
         'OC\\DB\\SQLiteMigrator' => __DIR__ . '/../../..' . '/lib/private/DB/SQLiteMigrator.php',
         'OC\\DB\\SQLiteSessionInit' => __DIR__ . '/../../..' . '/lib/private/DB/SQLiteSessionInit.php',

lib/private/DB/Connection.php

@@ -23,12 +23,19 @@ use Doctrine\DBAL\Platforms\SqlitePlatform;
 use Doctrine\DBAL\Result;
 use Doctrine\DBAL\Schema\Schema;
 use Doctrine\DBAL\Statement;
-use OC\DB\QueryBuilder\Partitioned\PartitionSplit;
 use OC\DB\QueryBuilder\Partitioned\PartitionedQueryBuilder;
+use OC\DB\QueryBuilder\Partitioned\PartitionSplit;
 use OC\DB\QueryBuilder\QueryBuilder;
+use OC\DB\QueryBuilder\Sharded\AutoIncrementHandler;
+use OC\DB\QueryBuilder\Sharded\CrossShardMoveHelper;
+use OC\DB\QueryBuilder\Sharded\RoundRobinShardMapper;
+use OC\DB\QueryBuilder\Sharded\ShardConnectionManager;
+use OC\DB\QueryBuilder\Sharded\ShardDefinition;
 use OC\SystemConfig;
 use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\DB\QueryBuilder\Sharded\IShardMapper;
 use OCP\Diagnostics\IEventLogger;
+use OCP\ICacheFactory;
 use OCP\IDBConnection;
 use OCP\IRequestId;
 use OCP\PreConditionNotMetException;
@@ -79,6 +86,10 @@ class Connection extends PrimaryReadReplicaConnection {
 
 	/** @var array<string, list<string>> */
 	protected array $partitions;
+	/** @var ShardDefinition[] */
+	protected array $shards = [];
+	protected ShardConnectionManager $shardConnectionManager;
+	protected AutoIncrementHandler $autoIncrementHandler;
 
 	/**
 	 * Initializes a new instance of the Connection class.
@@ -104,6 +115,13 @@ class Connection extends PrimaryReadReplicaConnection {
 		$this->adapter = new $params['adapter']($this);
 		$this->tablePrefix = $params['tablePrefix'];
 
+		/** @psalm-suppress InvalidArrayOffset */
+		$this->shardConnectionManager = $this->params['shard_connection_manager'] ?? Server::get(ShardConnectionManager::class);
+		/** @psalm-suppress InvalidArrayOffset */
+		$this->autoIncrementHandler = $this->params['auto_increment_handler'] ?? new AutoIncrementHandler(
+			Server::get(ICacheFactory::class),
+			$this->shardConnectionManager,
+		);
 		$this->systemConfig = \OC::$server->getSystemConfig();
 		$this->clock = Server::get(ClockInterface::class);
 		$this->logger = Server::get(LoggerInterface::class);
@@ -122,11 +140,44 @@ class Connection extends PrimaryReadReplicaConnection {
 			$this->_config->setSQLLogger($debugStack);
 		}
 
-		$this->partitions = $this->systemConfig->getValue('db.partitions', []);
+		// todo: only allow specific, pre-defined shard configurations, the current config exists for easy testing setup
+		$this->shards = array_map(function (array $config) {
+			$shardMapperClass = $config['mapper'] ?? RoundRobinShardMapper::class;
+			$shardMapper = Server::get($shardMapperClass);
+			if (!$shardMapper instanceof IShardMapper) {
+				throw new \Exception("Invalid shard mapper: $shardMapperClass");
+			}
+			return new ShardDefinition(
+				$config['table'],
+				$config['primary_key'],
+				$config['companion_keys'],
+				$config['shard_key'],
+				$shardMapper,
+				$config['companion_tables'],
+				$config['shards']
+			);
+		}, $this->params['sharding']);
+		$this->partitions = array_map(function (ShardDefinition $shard) {
+			return array_merge([$shard->table], $shard->companionTables);
+		}, $this->shards);
 
 		$this->setNestTransactionsWithSavepoints(true);
 	}
 
+	/**
+	 * @return IDBConnection[]
+	 */
+	public function getShardConnections(): array {
+		$connections = [];
+		foreach ($this->shards as $shardDefinition) {
+			foreach ($shardDefinition->getAllShards() as $shard) {
+				/** @var ConnectionAdapter $connection */
+				$connections[] = $this->shardConnectionManager->getConnection($shardDefinition, $shard);
+			}
+		}
+		return $connections;
+	}
+
 	/**
 	 * @throws Exception
 	 */
@@ -175,13 +226,19 @@ class Connection extends PrimaryReadReplicaConnection {
 	 */
 	public function getQueryBuilder(): IQueryBuilder {
 		$this->queriesBuilt++;
+
 		$builder = new QueryBuilder(
 			new ConnectionAdapter($this),
 			$this->systemConfig,
 			$this->logger
 		);
 		if (count($this->partitions) > 0) {
-			$builder = new PartitionedQueryBuilder($builder);
+			$builder = new PartitionedQueryBuilder(
+				$builder,
+				$this->shards,
+				$this->shardConnectionManager,
+				$this->autoIncrementHandler,
+			);
 			foreach ($this->partitions as $name => $tables) {
 				$partition = new PartitionSplit($name, $tables);
 				$builder->addPartition($partition);
@@ -703,6 +760,9 @@ class Connection extends PrimaryReadReplicaConnection {
 			return $migrator->generateChangeScript($toSchema);
 		} else {
 			$migrator->migrate($toSchema);
+			foreach ($this->getShardConnections() as $shardConnection) {
+				$shardConnection->migrateToSchema($toSchema);
+			}
 		}
 	}
 
@@ -819,4 +879,12 @@ class Connection extends PrimaryReadReplicaConnection {
 			}
 		}
 	}
+
+	public function getShardDefinition(string $name): ?ShardDefinition {
+		return $this->shards[$name] ?? null;
+	}
+
+	public function getCrossShardMoveHelper(): CrossShardMoveHelper {
+		return new CrossShardMoveHelper($this->shardConnectionManager);
+	}
 }

lib/private/DB/ConnectionAdapter.php

@@ -12,6 +12,8 @@ use Doctrine\DBAL\Exception;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
 use Doctrine\DBAL\Schema\Schema;
 use OC\DB\Exceptions\DbalException;
+use OC\DB\QueryBuilder\Sharded\CrossShardMoveHelper;
+use OC\DB\QueryBuilder\Sharded\ShardDefinition;
 use OCP\DB\IPreparedStatement;
 use OCP\DB\IResult;
 use OCP\DB\QueryBuilder\IQueryBuilder;
@@ -244,4 +246,12 @@ class ConnectionAdapter implements IDBConnection {
 	public function logDatabaseException(\Exception $exception) {
 		$this->inner->logDatabaseException($exception);
 	}
+
+	public function getShardDefinition(string $name): ?ShardDefinition {
+		return $this->inner->getShardDefinition($name);
+	}
+
+	public function getCrossShardMoveHelper(): CrossShardMoveHelper {
+		return $this->inner->getCrossShardMoveHelper();
+	}
 }

lib/private/DB/ConnectionFactory.php

@@ -11,7 +11,11 @@ use Doctrine\Common\EventManager;
 use Doctrine\DBAL\Configuration;
 use Doctrine\DBAL\DriverManager;
 use Doctrine\DBAL\Event\Listeners\OracleSessionInit;
+use OC\DB\QueryBuilder\Sharded\AutoIncrementHandler;
+use OC\DB\QueryBuilder\Sharded\ShardConnectionManager;
 use OC\SystemConfig;
+use OCP\ICacheFactory;
+use OCP\Server;
 
 /**
  * Takes care of creating and configuring Doctrine connections.
@@ -54,9 +58,12 @@ class ConnectionFactory {
 		],
 	];
 
+	private ShardConnectionManager $shardConnectionManager;
+	private ICacheFactory $cacheFactory;
 
 	public function __construct(
-		private SystemConfig $config
+		private SystemConfig $config,
+		?ICacheFactory $cacheFactory = null,
 	) {
 		if ($this->config->getValue('mysql.utf8mb4', false)) {
 			$this->defaultConnectionParams['mysql']['charset'] = 'utf8mb4';
@@ -65,6 +72,8 @@ class ConnectionFactory {
 		if ($collationOverride) {
 			$this->defaultConnectionParams['mysql']['collation'] = $collationOverride;
 		}
+		$this->shardConnectionManager = new ShardConnectionManager($this->config, $this);
+		$this->cacheFactory = $cacheFactory ?? Server::get(ICacheFactory::class);
 	}
 
 	/**
@@ -214,6 +223,14 @@ class ConnectionFactory {
 		if ($this->config->getValue('dbpersistent', false)) {
 			$connectionParams['persistent'] = true;
 		}
+
+		$connectionParams['sharding'] = $this->config->getValue('dbsharding', []);
+		$connectionParams['shard_connection_manager'] = $this->shardConnectionManager;
+		$connectionParams['auto_increment_handler'] = new AutoIncrementHandler(
+			$this->cacheFactory,
+			$this->shardConnectionManager,
+		);
+
 		$connectionParams = array_merge($connectionParams, $additionalConnectionParams);
 
 		$replica = $this->config->getValue($configPrefix . 'dbreplica', $this->config->getValue('dbreplica', [])) ?: [$connectionParams];

lib/private/DB/QueryBuilder/ExtendedQueryBuilder.php

@@ -289,7 +289,21 @@ abstract class ExtendedQueryBuilder implements IQueryBuilder {
 		return $this->builder->executeStatement($connection);
 	}
 
+	public function hintShardKey(string $column, mixed $value) {
+		$this->builder->hintShardKey($column, $value);
+		return $this;
+	}
+
+	public function runAcrossAllShards() {
+		$this->builder->runAcrossAllShards();
+		return $this;
+	}
+
 	public function getOutputColumns(): array {
 		return $this->builder->getOutputColumns();
 	}
+
+	public function prefixTableName(string $table): string {
+		return $this->builder->prefixTableName($table);
+	}
 }

lib/private/DB/QueryBuilder/Partitioned/JoinCondition.php

@@ -44,7 +44,7 @@ class JoinCondition {
 		$fromConditions = [];
 		$toConditions = [];
 		foreach ($conditions as $condition) {
-			if (($condition->fromColumn && $fromColumn) ||($condition->toColumn && $toColumn)) {
+			if (($condition->fromColumn && $fromColumn) || ($condition->toColumn && $toColumn)) {
 				throw new InvalidPartitionedQueryException("Can't join from {$condition->fromColumn} to {$condition->toColumn} as it already join froms {$fromColumn} to {$toColumn}");
 			}
 			if ($condition->fromColumn) {

lib/private/DB/QueryBuilder/Partitioned/PartitionQuery.php

@@ -14,12 +14,12 @@ use OCP\DB\QueryBuilder\IQueryBuilder;
  * A sub-query from a partitioned join
  */
 class PartitionQuery {
-	const JOIN_MODE_INNER = 'inner';
-	const JOIN_MODE_LEFT = 'left';
+	public const JOIN_MODE_INNER = 'inner';
+	public const JOIN_MODE_LEFT = 'left';
 	// left-join where the left side IS NULL
-	const JOIN_MODE_LEFT_NULL = 'left_null';
+	public const JOIN_MODE_LEFT_NULL = 'left_null';
 
-	const JOIN_MODE_RIGHT = 'right';
+	public const JOIN_MODE_RIGHT = 'right';
 
 	public function __construct(
 		public IQueryBuilder $query,

lib/private/DB/QueryBuilder/Partitioned/PartitionedQueryBuilder.php

@@ -8,18 +8,15 @@ declare(strict_types=1);
 
 namespace OC\DB\QueryBuilder\Partitioned;
 
-use OC\DB\ConnectionAdapter;
 use OC\DB\QueryBuilder\CompositeExpression;
-use OC\DB\QueryBuilder\ExtendedQueryBuilder;
 use OC\DB\QueryBuilder\QuoteHelper;
+use OC\DB\QueryBuilder\Sharded\AutoIncrementHandler;
 use OC\DB\QueryBuilder\Sharded\ShardConnectionManager;
 use OC\DB\QueryBuilder\Sharded\ShardedQueryBuilder;
-use OC\SystemConfig;
 use OCP\DB\IResult;
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\DB\QueryBuilder\IQueryFunction;
 use OCP\IDBConnection;
-use Psr\Log\LoggerInterface;
 
 /**
  * A special query builder that automatically splits queries that span across multiple database partitions[1].
@@ -38,7 +35,7 @@ use Psr\Log\LoggerInterface;
  *
  * [1]: A set of tables which can't be queried together with the rest of the tables, such as when sharding is used.
  */
-class PartitionedQueryBuilder extends ExtendedQueryBuilder {
+class PartitionedQueryBuilder extends ShardedQueryBuilder {
 	/** @var array<string, PartitionQuery> $splitQueries */
 	private array $splitQueries = [];
 	/** @var list<PartitionSplit> */
@@ -53,14 +50,28 @@ class PartitionedQueryBuilder extends ExtendedQueryBuilder {
 	private ?int $offset = null;
 
 	public function __construct(
-		IQueryBuilder                  $builder,
+		IQueryBuilder          $builder,
+		array                  $shardDefinitions,
+		ShardConnectionManager $shardConnectionManager,
+		AutoIncrementHandler   $autoIncrementHandler,
 	) {
-		parent::__construct($builder);
+		parent::__construct($builder, $shardDefinitions, $shardConnectionManager, $autoIncrementHandler);
 		$this->quoteHelper = new QuoteHelper();
 	}
 
 	private function newQuery(): IQueryBuilder {
-		return $this->builder->getConnection()->getQueryBuilder();
+		// get a fresh, non-partitioning query builder
+		$builder = $this->builder->getConnection()->getQueryBuilder();
+		if ($builder instanceof PartitionedQueryBuilder) {
+			$builder = $builder->builder;
+		}
+
+		return new ShardedQueryBuilder(
+			$builder,
+			$this->shardDefinitions,
+			$this->shardConnectionManager,
+			$this->autoIncrementHandler,
+		);
 	}
 
 	// we need to save selects until we know all the table aliases
@@ -70,8 +81,8 @@ class PartitionedQueryBuilder extends ExtendedQueryBuilder {
 		return $this;
 	}
 
-	public function addSelect(...$selects) {
-		$selects = array_map(function($select) {
+	public function addSelect(...$select) {
+		$select = array_map(function ($select) {
 			return ['select' => $select, 'alias' => null];
 		}, $select);
 		$this->selects = array_merge($this->selects, $select);
@@ -281,7 +292,7 @@ class PartitionedQueryBuilder extends ExtendedQueryBuilder {
 
 		$partitionPredicates = [];
 		foreach ($predicates as $predicate) {
-			$partition = $this->getPartitionForPredicate((string) $predicate);
+			$partition = $this->getPartitionForPredicate((string)$predicate);
 			if ($this->mainPartition === $partition) {
 				$partitionPredicates[''][] = $predicate;
 			} elseif ($partition) {

lib/private/DB/QueryBuilder/QueryBuilder.php

@@ -1329,7 +1329,7 @@ class QueryBuilder implements IQueryBuilder {
 	 * @param string $table
 	 * @return string
 	 */
-	public function prefixTableName($table) {
+	public function prefixTableName(string $table): string {
 		if ($this->automaticTablePrefix === false || str_starts_with($table, '*PREFIX*')) {
 			return $table;
 		}

lib/private/DB/QueryBuilder/Sharded/AutoIncrementHandler.php

@@ -0,0 +1,152 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+use OCP\ICacheFactory;
+use OCP\IMemcache;
+use OCP\IMemcacheTTL;
+
+/**
+ * A helper to atomically determine the next auto increment value for a sharded table
+ *
+ * Since we can't use the database's auto-increment (since each db doesn't know about the keys in the other shards)
+ * we need external logic for doing the auto increment
+ */
+class AutoIncrementHandler {
+	public const MIN_VALID_KEY = 1000;
+	public const TTL = 365 * 24 * 60 * 60;
+
+	private ?IMemcache $cache = null;
+
+	public function __construct(
+		private ICacheFactory                  $cacheFactory,
+		private ShardConnectionManager $shardConnectionManager,
+	) {
+		if (PHP_INT_SIZE < 8) {
+			throw new \Exception("sharding is only supported with 64bit php");
+		}
+	}
+
+	private function getCache(): IMemcache {
+		if(is_null($this->cache)) {
+			$cache = $this->cacheFactory->createDistributed("shared_autoincrement");
+			if ($cache instanceof IMemcache) {
+				$this->cache = $cache;
+			} else {
+				throw new \Exception('Distributed cache ' . get_class($cache) . ' is not suitable');
+			}
+		}
+		return $this->cache;
+	}
+
+	/**
+	 * Get the next value for the given shard definition
+	 *
+	 * The returned key is unique and incrementing, but not sequential.
+	 * The shard id is encoded in the first byte of the returned value
+	 *
+	 * @param ShardDefinition $shardDefinition
+	 * @return int
+	 * @throws \Exception
+	 */
+	public function getNextPrimaryKey(ShardDefinition $shardDefinition, int $shard): int {
+		$retries = 0;
+		while ($retries < 5) {
+			$next = $this->getNextInner($shardDefinition);
+			if ($next !== null) {
+				if ($next > ShardDefinition::MAX_PRIMARY_KEY) {
+					throw new \Exception("Max primary key of " . ShardDefinition::MAX_PRIMARY_KEY . " exceeded");
+				}
+				// we encode the shard the primary key was originally inserted into to allow guessing the shard by primary key later on
+				return ($next << 8) | $shard;
+			} else {
+				$retries++;
+			}
+		}
+		throw new \Exception("Failed to get next primary key");
+	}
+
+	/**
+	 * auto increment logic without retry
+	 *
+	 * @param ShardDefinition $shardDefinition
+	 * @return int|null either the next primary key or null if the call needs to be retried
+	 */
+	private function getNextInner(ShardDefinition $shardDefinition): ?int {
+		$cache = $this->getCache();
+		// because this function will likely be called concurrently from different requests
+		// the implementation needs to ensure that the cached value can be cleared, invalidated or re-calculated at any point between our cache calls
+		// care must be taken that the logic remains fully resilient against race conditions
+
+		// in the ideal case, the last primary key is stored in the cache and we can just do an `inc`
+		// if that is not the case we find the highest used id in the database increment it, and save it in the cache
+
+		// prevent inc from returning `1` if the key doesn't exist by setting it to a non-numeric value
+		$cache->add($shardDefinition->table, "empty-placeholder", self::TTL);
+		$next = $cache->inc($shardDefinition->table);
+
+		if ($cache instanceof IMemcacheTTL) {
+			$cache->setTTL($shardDefinition->table, self::TTL);
+		}
+
+		// the "add + inc" trick above isn't strictly atomic, so as a safety we reject any result that to small
+		// to handle the edge case of the stored value disappearing between the add and inc
+		if (is_int($next) && $next >= self::MIN_VALID_KEY) {
+			return $next;
+		} elseif (is_int($next)) {
+			// we hit the edge case, so invalidate the cached value
+			if (!$cache->cas($shardDefinition->table, $next, "empty-placeholder")) {
+				// someone else is changing the value concurrently, give up and retry
+				return null;
+			}
+		}
+
+		// discard the encoded initial shard
+		$current = $this->getMaxFromDb($shardDefinition) >> 8;
+		$next = max($current, self::MIN_VALID_KEY) + 1;
+		if ($cache->cas($shardDefinition->table, "empty-placeholder", $next)) {
+			return $next;
+		}
+
+		// another request set the cached value before us, so we should just be able to inc
+		$next = $cache->inc($shardDefinition->table);
+		if (is_int($next) && $next >= self::MIN_VALID_KEY) {
+			return $next;
+		} elseif(is_int($next)) {
+			// key got cleared, invalidate and retry
+			$cache->cas($shardDefinition->table, $next, "empty-placeholder");
+			return null;
+		} else {
+			// cleanup any non-numeric value other than the placeholder if that got stored somehow
+			$cache->ncad($shardDefinition->table, "empty-placeholder");
+			// retry
+			return null;
+		}
+	}
+
+	/**
+	 * Get the maximum primary key value from the shards
+	 */
+	private function getMaxFromDb(ShardDefinition $shardDefinition): int {
+		$max = 0;
+		foreach ($shardDefinition->getAllShards() as $shard) {
+			$connection = $this->shardConnectionManager->getConnection($shardDefinition, $shard);
+			$query = $connection->getQueryBuilder();
+			$query->select($shardDefinition->primaryKey)
+				->from($shardDefinition->table)
+				->orderBy($shardDefinition->primaryKey, "DESC")
+				->setMaxResults(1);
+			$result = $query->executeQuery()->fetchOne();
+			if ($result) {
+				$max = max($max, $result);
+			}
+		}
+		return $max;
+	}
+}

lib/private/DB/QueryBuilder/Sharded/CrossShardMoveHelper.php

@@ -0,0 +1,162 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+
+/**
+ * Utility methods for implementing logic that moves data across shards
+ */
+class CrossShardMoveHelper {
+	public function __construct(
+		private ShardConnectionManager $connectionManager
+	) {
+	}
+
+	public function getConnection(ShardDefinition $shardDefinition, int $shardKey): IDBConnection {
+		return $this->connectionManager->getConnection($shardDefinition, $shardDefinition->getShardForKey($shardKey));
+	}
+
+	/**
+	 * Update the shard key of a set of rows, moving them to a different shard if needed
+	 *
+	 * @param ShardDefinition $shardDefinition
+	 * @param string $table
+	 * @param string $shardColumn
+	 * @param int $sourceShardKey
+	 * @param int $targetShardKey
+	 * @param string $primaryColumn
+	 * @param int[] $primaryKeys
+	 * @return void
+	 */
+	public function moveCrossShards(ShardDefinition $shardDefinition, string $table, string $shardColumn, int $sourceShardKey, int $targetShardKey, string $primaryColumn, array $primaryKeys): void {
+		$sourceShard = $shardDefinition->getShardForKey($sourceShardKey);
+		$targetShard = $shardDefinition->getShardForKey($targetShardKey);
+		$sourceConnection = $this->connectionManager->getConnection($shardDefinition, $sourceShard);
+		if ($sourceShard === $targetShard) {
+			$this->updateItems($sourceConnection, $table, $shardColumn, $targetShardKey, $primaryColumn, $primaryKeys);
+
+			return;
+		}
+		$targetConnection = $this->connectionManager->getConnection($shardDefinition, $targetShard);
+
+		$sourceItems = $this->loadItems($sourceConnection, $table, $primaryColumn, $primaryKeys);
+		foreach ($sourceItems as &$sourceItem) {
+			$sourceItem[$shardColumn] = $targetShardKey;
+		}
+		if (!$sourceItems) {
+			return;
+		}
+
+		$sourceConnection->beginTransaction();
+		$targetConnection->beginTransaction();
+		try {
+			$this->saveItems($targetConnection, $table, $sourceItems);
+			$this->deleteItems($sourceConnection, $table, $primaryColumn, $primaryKeys);
+
+			$targetConnection->commit();
+			$sourceConnection->commit();
+		} catch (\Exception $e) {
+			$sourceConnection->rollback();
+			$targetConnection->rollback();
+			throw $e;
+		}
+	}
+
+	/**
+	 * Load rows from a table to move
+	 *
+	 * @param IDBConnection $connection
+	 * @param string $table
+	 * @param string $primaryColumn
+	 * @param int[] $primaryKeys
+	 * @return array[]
+	 */
+	public function loadItems(IDBConnection $connection, string $table, string $primaryColumn, array $primaryKeys): array {
+		$query = $connection->getQueryBuilder();
+		$query->select('*')
+			->from($table)
+			->where($query->expr()->in($primaryColumn, $query->createParameter("keys")));
+
+		$chunks = array_chunk($primaryKeys, 1000);
+
+		$results = [];
+		foreach ($chunks as $chunk) {
+			$query->setParameter("keys", $chunk, IQueryBuilder::PARAM_INT_ARRAY);
+			$results = array_merge($results, $query->execute()->fetchAll());
+		}
+
+		return $results;
+	}
+
+	/**
+	 * Save modified rows
+	 *
+	 * @param IDBConnection $connection
+	 * @param string $table
+	 * @param array[] $items
+	 * @return void
+	 */
+	public function saveItems(IDBConnection $connection, string $table, array $items): void {
+		if (count($items) === 0) {
+			return;
+		}
+		$query = $connection->getQueryBuilder();
+		$query->insert($table);
+		foreach ($items[0] as $column => $value) {
+			$query->setValue($column, $query->createParameter($column));
+		}
+
+		foreach ($items as $item) {
+			foreach ($item as $column => $value) {
+				if (is_int($column)) {
+					$query->setParameter($column, $value, IQueryBuilder::PARAM_INT);
+				} else {
+					$query->setParameter($column, $value);
+				}
+			}
+			$query->executeStatement();
+		}
+	}
+
+	/**
+	 * @param IDBConnection $connection
+	 * @param string $table
+	 * @param string $primaryColumn
+	 * @param int[] $primaryKeys
+	 * @return void
+	 */
+	public function updateItems(IDBConnection $connection, string $table, string $shardColumn, int $targetShardKey, string $primaryColumn, array $primaryKeys): void {
+		$query = $connection->getQueryBuilder();
+		$query->update($table)
+			->set($shardColumn, $query->createNamedParameter($targetShardKey, IQueryBuilder::PARAM_INT))
+			->where($query->expr()->in($primaryColumn, $query->createNamedParameter($primaryKeys, IQueryBuilder::PARAM_INT_ARRAY)));
+		$query->executeQuery()->fetchAll();
+	}
+
+	/**
+	 * @param IDBConnection $connection
+	 * @param string $table
+	 * @param string $primaryColumn
+	 * @param int[] $primaryKeys
+	 * @return void
+	 */
+	public function deleteItems(IDBConnection $connection, string $table, string $primaryColumn, array $primaryKeys): void {
+		$query = $connection->getQueryBuilder();
+		$query->delete($table)
+			->where($query->expr()->in($primaryColumn, $query->createParameter("keys")));
+		$chunks = array_chunk($primaryKeys, 1000);
+
+		foreach ($chunks as $chunk) {
+			$query->setParameter("keys", $chunk, IQueryBuilder::PARAM_INT_ARRAY);
+			$query->executeStatement();
+		}
+	}
+}

lib/private/DB/QueryBuilder/Sharded/HashShardMapper.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+use OCP\DB\QueryBuilder\Sharded\IShardMapper;
+
+/**
+ * Map string key to an int-range by hashing the key
+ */
+class HashShardMapper implements IShardMapper {
+	public function getShardForKey(int $key, int $count): int {
+		$int = unpack('L', substr(md5((string)$key, true), 0, 4))[1];
+		return $int % $count;
+	}
+}

lib/private/DB/QueryBuilder/Sharded/InvalidShardedQueryException.php

@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+/**
+ * Queries on sharded table has the following limitations:
+ *
+ * 1. Either the shard key (e.g. "storage") or primary key (e.g. "fileid") must be mentioned in the query.
+ *    Or the query must be explicitly marked as running across all shards.
+ *
+ *    For queries where it isn't possible to set one of these keys in the query normally, you can set it using `hintShardKey`
+ *
+ * 2. Insert statements must always explicitly set the shard key
+ * 3. A query on a sharded table is not allowed to join on the same table
+ * 4. Right joins are not allowed on sharded tables
+ * 5. Updating the shard key where the new shard key maps to a different shard is not allowed
+ *
+ *    Moving rows to a different shard needs to be implemented manually. `CrossShardMoveHelper` provides
+ *    some tools to help make this easier.
+ */
+class InvalidShardedQueryException extends \Exception {
+
+}

lib/private/DB/QueryBuilder/Sharded/RoundRobinShardMapper.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+use OCP\DB\QueryBuilder\Sharded\IShardMapper;
+
+/**
+ * Map string key to an int-range by hashing the key
+ */
+class RoundRobinShardMapper implements IShardMapper {
+	public function getShardForKey(int $key, int $count): int {
+		return $key % $count;
+	}
+}

lib/private/DB/QueryBuilder/Sharded/ShardConnectionManager.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+use OC\DB\ConnectionAdapter;
+use OC\DB\ConnectionFactory;
+use OC\SystemConfig;
+use OCP\IDBConnection;
+
+/**
+ * Keeps track of the db connections to the various shards
+ */
+class ShardConnectionManager {
+	/** @var array<string, IDBConnection> */
+	private array $connections = [];
+
+	public function __construct(
+		private SystemConfig $config,
+		private ConnectionFactory $factory,
+	) {
+	}
+
+	public function getConnection(ShardDefinition $shardDefinition, int $shard): IDBConnection {
+		$connectionKey = $shardDefinition->table . '_' . $shard;
+		if (!isset($this->connections[$connectionKey])) {
+			$this->connections[$connectionKey] = $this->createConnection($shardDefinition->shards[$shard]);
+		}
+
+		return $this->connections[$connectionKey];
+	}
+
+	private function createConnection(array $shardConfig): IDBConnection {
+		$shardConfig['sharding'] = [];
+		$type = $this->config->getValue('dbtype', 'sqlite');
+		return new ConnectionAdapter($this->factory->getConnection($type, $shardConfig));
+	}
+}

lib/private/DB/QueryBuilder/Sharded/ShardDefinition.php

@@ -0,0 +1,66 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+use OCP\DB\QueryBuilder\Sharded\IShardMapper;
+
+/**
+ * Configuration for a shard setup
+ */
+class ShardDefinition {
+	// we reserve the bottom byte of the primary key for the initial shard, so the total shard count is limited to what we can fit there
+	public const MAX_SHARDS = 256;
+
+	public const PRIMARY_KEY_MASK = 0x7F_FF_FF_FF_FF_FF_FF_00;
+	public const PRIMARY_KEY_SHARD_MASK = 0x00_00_00_00_00_00_00_FF;
+	// since we reserve 1 byte for the shard index, we only have 56 bits of primary key space
+	public const MAX_PRIMARY_KEY = PHP_INT_MAX >> 8;
+
+	/**
+	 * @param string $table
+	 * @param string $primaryKey
+	 * @param string $shardKey
+	 * @param string[] $companionKeys
+	 * @param IShardMapper $shardMapper
+	 * @param string[] $companionTables
+	 * @param array $shards
+	 */
+	public function __construct(
+		public string $table,
+		public string $primaryKey,
+		public array $companionKeys,
+		public string $shardKey,
+		public IShardMapper $shardMapper,
+		public array $companionTables = [],
+		public array $shards = [],
+	) {
+		if (count($this->shards) >= self::MAX_SHARDS) {
+			throw new \Exception("Only allowed maximum of " . self::MAX_SHARDS . " shards allowed");
+		}
+	}
+
+	public function hasTable(string $table): bool {
+		if ($this->table === $table) {
+			return true;
+		}
+		return in_array($table, $this->companionTables);
+	}
+
+	public function getShardForKey(int $key): int {
+		return $this->shardMapper->getShardForKey($key, count($this->shards));
+	}
+
+	public function getAllShards(): array {
+		return array_keys($this->shards);
+	}
+
+	public function isKey(string $column): bool {
+		return $column === $this->primaryKey || in_array($column, $this->companionKeys);
+	}
+}

lib/private/DB/QueryBuilder/Sharded/ShardQueryRunner.php

@@ -0,0 +1,197 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+use OC\DB\ArrayResult;
+use OCP\DB\IResult;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+
+/**
+ * Logic for running a query across a number of shards, combining the results
+ */
+class ShardQueryRunner {
+	public function __construct(
+		private ShardConnectionManager $shardConnectionManager,
+		private ShardDefinition $shardDefinition,
+	) {
+	}
+
+	/**
+	 * Get the shards for a specific query or null if the shards aren't known in advance
+	 *
+	 * @param bool $allShards
+	 * @param int[] $shardKeys
+	 * @return null|int[]
+	 */
+	public function getShards(bool $allShards, array $shardKeys): ?array {
+		if ($allShards) {
+			return $this->shardDefinition->getAllShards();
+		}
+		$allConfiguredShards = $this->shardDefinition->getAllShards();
+		if (count($allConfiguredShards) === 1) {
+			return $allConfiguredShards;
+		}
+		if (empty($shardKeys)) {
+			return null;
+		}
+		$shards = array_map(function ($shardKey) {
+			return $this->shardDefinition->getShardForKey((int)$shardKey);
+		}, $shardKeys);
+		return array_values(array_unique($shards));
+	}
+
+	/**
+	 * Try to get the shards that the keys are likely to be in, based on the shard the row was created
+	 *
+	 * @param int[] $primaryKeys
+	 * @return int[]
+	 */
+	private function getLikelyShards(array $primaryKeys): array {
+		$shards = [];
+		foreach ($primaryKeys as $primaryKey) {
+			$encodedShard = $primaryKey & ShardDefinition::PRIMARY_KEY_SHARD_MASK;
+			if ($encodedShard < count($this->shardDefinition->shards) && !in_array($encodedShard, $shards)) {
+				$shards[] = $encodedShard;
+			}
+		}
+		return $shards;
+	}
+
+	/**
+	 * Execute a SELECT statement across the configured shards
+	 *
+	 * @param IQueryBuilder $query
+	 * @param bool $allShards
+	 * @param int[] $shardKeys
+	 * @param int[] $primaryKeys
+	 * @param array{column: string, order: string}[] $sortList
+	 * @param int|null $limit
+	 * @param int|null $offset
+	 * @return IResult
+	 */
+	public function executeQuery(
+		IQueryBuilder $query,
+		bool          $allShards,
+		array         $shardKeys,
+		array         $primaryKeys,
+		?array        $sortList = null,
+		?int          $limit = null,
+		?int          $offset = null,
+	): IResult {
+		$shards = $this->getShards($allShards, $shardKeys);
+		$results = [];
+		if ($shards && count($shards) === 1) {
+			// trivial case
+			return $query->executeQuery($this->shardConnectionManager->getConnection($this->shardDefinition, $shards[0]));
+		}
+		// we have to emulate limit and offset, so we select offset+limit from all shards to ensure we have enough rows
+		// and then filter them down after we merged the results
+		if ($limit !== null && $offset !== null) {
+			$query->setMaxResults($limit + $offset);
+		}
+
+		if ($shards) {
+			// we know exactly what shards we need to query
+			foreach ($shards as $shard) {
+				$shardConnection = $this->shardConnectionManager->getConnection($this->shardDefinition, $shard);
+				$subResult = $query->executeQuery($shardConnection);
+				$results = array_merge($results, $subResult->fetchAll());
+				$subResult->closeCursor();
+			}
+		} else {
+			// we don't know for sure what shards we need to query,
+			// we first try the shards that are "likely" to have the rows we want, based on the shard that the row was
+			// originally created in. If we then still haven't found all rows we try the rest of the shards
+			$likelyShards = $this->getLikelyShards($primaryKeys);
+			$unlikelyShards = array_diff($this->shardDefinition->getAllShards(), $likelyShards);
+			$shards = array_merge($likelyShards, $unlikelyShards);
+
+			foreach ($shards as $shard) {
+				$shardConnection = $this->shardConnectionManager->getConnection($this->shardDefinition, $shard);
+				$subResult = $query->executeQuery($shardConnection);
+				$rows = $subResult->fetchAll();
+				$results = array_merge($results, $rows);
+				$subResult->closeCursor();
+
+				if (count($rows) >= count($primaryKeys)) {
+					// we have all the rows we're looking for
+					break;
+				}
+			}
+		}
+
+		if ($sortList) {
+			usort($results, function ($a, $b) use ($sortList) {
+				foreach ($sortList as $sort) {
+					$valueA = $a[$sort['column']] ?? null;
+					$valueB = $b[$sort['column']] ?? null;
+					$cmp = $valueA <=> $valueB;
+					if ($cmp === 0) {
+						continue;
+					}
+					if ($sort['order'] === "DESC") {
+						$cmp = -$cmp;
+					}
+					return $cmp;
+				}
+			});
+		}
+
+		if ($limit !== null && $offset !== null) {
+			$results = array_slice($results, $offset, $limit);
+		} elseif ($limit !== null) {
+			$results = array_slice($results, 0, $limit);
+		} elseif ($offset !== null) {
+			$results = array_slice($results, $offset);
+		}
+
+		return new ArrayResult($results);
+	}
+
+	/**
+	 * Execute an UPDATE or DELETE statement
+	 *
+	 * @param IQueryBuilder $query
+	 * @param bool $allShards
+	 * @param int[] $shardKeys
+	 * @param int[] $primaryKeys
+	 * @return int
+	 * @throws \OCP\DB\Exception
+	 */
+	public function executeStatement(IQueryBuilder $query, bool $allShards, array $shardKeys, array $primaryKeys): int {
+		if ($query->getType() === \Doctrine\DBAL\Query\QueryBuilder::INSERT) {
+			throw new \Exception("insert queries need special handling");
+		}
+
+		$shards = $this->getShards($allShards, $shardKeys);
+		$maxCount = count($primaryKeys);
+		if ($shards && count($shards) === 1) {
+			return $query->executeStatement($this->shardConnectionManager->getConnection($this->shardDefinition, $shards[0]));
+		} elseif ($shards) {
+			$maxCount = PHP_INT_MAX;
+		} else {
+			// sort the likely shards before the rest, similar logic to `self::executeQuery`
+			$likelyShards = $this->getLikelyShards($primaryKeys);
+			$unlikelyShards = array_diff($this->shardDefinition->getAllShards(), $likelyShards);
+			$shards = array_merge($likelyShards, $unlikelyShards);
+		}
+
+		$count = 0;
+
+		foreach ($shards as $shard) {
+			$shardConnection = $this->shardConnectionManager->getConnection($this->shardDefinition, $shard);
+			$count += $query->executeStatement($shardConnection);
+
+			if ($count >= $maxCount) {
+				break;
+			}
+		}
+		return $count;
+	}
+}

lib/private/DB/QueryBuilder/Sharded/ShardedQueryBuilder.php

@@ -0,0 +1,403 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\DB\QueryBuilder\Sharded;
+
+use OC\DB\QueryBuilder\CompositeExpression;
+use OC\DB\QueryBuilder\ExtendedQueryBuilder;
+use OC\DB\QueryBuilder\Parameter;
+use OCP\DB\IResult;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+
+/**
+ * A special query builder that automatically distributes queries over multiple database shards.
+ *
+ * This relies on `PartitionedQueryBuilder` to handle splitting of parts of the query that touch the sharded tables
+ * from the non-sharded tables. So the query build here should only either touch only sharded table or only non-sharded tables.
+ *
+ * Most of the logic in this class is concerned with extracting either the shard key (e.g. "storage") or primary key (e.g. "fileid")
+ * from the query. The logic for actually running the query across the shards is mostly delegated to `ShardQueryRunner`.
+ */
+class ShardedQueryBuilder extends ExtendedQueryBuilder {
+	private array $shardKeys = [];
+	private array $primaryKeys = [];
+	private ?ShardDefinition $shardDefinition = null;
+	/** @var bool Run the query across all shards */
+	private bool $allShards = false;
+	private ?string $insertTable = null;
+	private mixed $lastInsertId = null;
+	private ?IDBConnection $lastInsertConnection = null;
+	private ?int $updateShardKey = null;
+	private ?int $limit = null;
+	private ?int $offset = null;
+	/** @var array{column: string, order: string}[]  */
+	private array $sortList = [];
+	private string $mainTable = '';
+
+	public function __construct(
+		IQueryBuilder                  $builder,
+		protected array                  $shardDefinitions,
+		protected ShardConnectionManager $shardConnectionManager,
+		protected AutoIncrementHandler $autoIncrementHandler,
+	) {
+		parent::__construct($builder);
+	}
+
+	public function getShardKeys(): array {
+		return $this->getKeyValues($this->shardKeys);
+	}
+
+	public function getPrimaryKeys(): array {
+		return $this->getKeyValues($this->primaryKeys);
+	}
+
+	private function getKeyValues(array $keys): array {
+		$values = [];
+		foreach ($keys as $key) {
+			$values = array_merge($values, $this->getKeyValue($key));
+		}
+		return array_values(array_unique($values));
+	}
+
+	private function getKeyValue($value): array {
+		if ($value instanceof Parameter) {
+			$value = (string)$value;
+		}
+		if (is_string($value) && str_starts_with($value, ':')) {
+			$param = $this->getParameter(substr($value, 1));
+			if (is_array($param)) {
+				return $param;
+			} else {
+				return [$param];
+			}
+		} elseif ($value !== null) {
+			return [$value];
+		} else {
+			return [];
+		}
+	}
+
+	public function where(...$predicates) {
+		return $this->andWhere(...$predicates);
+	}
+
+	public function andWhere(...$where) {
+		if ($where) {
+			foreach ($where as $predicate) {
+				$this->tryLoadShardKey($predicate);
+			}
+			parent::andWhere(...$where);
+		}
+		return $this;
+	}
+
+	private function tryLoadShardKey($predicate): void {
+		if (!$this->shardDefinition) {
+			return;
+		}
+		if ($keys = $this->tryExtractShardKeys($predicate, $this->shardDefinition->shardKey)) {
+			$this->shardKeys += $keys;
+		}
+		if ($keys = $this->tryExtractShardKeys($predicate, $this->shardDefinition->primaryKey)) {
+			$this->primaryKeys += $keys;
+		}
+		foreach ($this->shardDefinition->companionKeys as $companionKey) {
+			if ($keys = $this->tryExtractShardKeys($predicate, $companionKey)) {
+				$this->primaryKeys += $keys;
+			}
+		}
+	}
+
+	/**
+	 * @param $predicate
+	 * @param string $column
+	 * @return string[]
+	 */
+	private function tryExtractShardKeys($predicate, string $column): array {
+		if ($predicate instanceof CompositeExpression) {
+			$values = [];
+			foreach ($predicate->getParts() as $part) {
+				$partValues = $this->tryExtractShardKeys($part, $column);
+				// for OR expressions, we can only rely on the predicate if all parts contain the comparison
+				if ($predicate->getType() === CompositeExpression::TYPE_OR && !$partValues) {
+					return [];
+				}
+				$values = array_merge($values, $partValues);
+			}
+			return $values;
+		}
+		$predicate = (string)$predicate;
+		// expect a condition in the form of 'alias1.column1 = placeholder' or 'alias1.column1 in placeholder'
+		if (substr_count($predicate, ' ') > 2) {
+			return [];
+		}
+		if (str_contains($predicate, ' = ')) {
+			$parts = explode(' = ', $predicate);
+			if ($parts[0] === "`{$column}`" || str_ends_with($parts[0], "`.`{$column}`")) {
+				return [$parts[1]];
+			} else {
+				return [];
+			}
+		}
+
+		if (str_contains($predicate, ' IN ')) {
+			$parts = explode(' IN ', $predicate);
+			if ($parts[0] === "`{$column}`" || str_ends_with($parts[0], "`.`{$column}`")) {
+				return [trim(trim($parts[1], '('), ')')];
+			} else {
+				return [];
+			}
+		}
+
+		return [];
+	}
+
+	public function set($key, $value) {
+		if ($this->shardDefinition && $key === $this->shardDefinition->shardKey) {
+			$updateShardKey = $value;
+		}
+		return parent::set($key, $value);
+	}
+
+	public function setValue($column, $value) {
+		if ($this->shardDefinition) {
+			if ($this->shardDefinition->isKey($column)) {
+				$this->primaryKeys[] = $value;
+			}
+			if ($column === $this->shardDefinition->shardKey) {
+				$this->shardKeys[] = $value;
+			}
+		}
+		return parent::setValue($column, $value);
+	}
+
+	public function values(array $values) {
+		foreach ($values as $column => $value) {
+			$this->setValue($column, $value);
+		}
+		return $this;
+	}
+
+	private function actOnTable(string $table): void {
+		$this->mainTable = $table;
+		foreach ($this->shardDefinitions as $shardDefinition) {
+			if ($shardDefinition->hasTable($table)) {
+				$this->shardDefinition = $shardDefinition;
+			}
+		}
+	}
+
+	public function from($from, $alias = null) {
+		if (is_string($from) && $from) {
+			$this->actOnTable($from);
+		}
+		return parent::from($from, $alias);
+	}
+
+	public function update($update = null, $alias = null) {
+		if (is_string($update) && $update) {
+			$this->actOnTable($update);
+		}
+		return parent::update($update, $alias);
+	}
+
+	public function insert($insert = null) {
+		if (is_string($insert) && $insert) {
+			$this->insertTable = $insert;
+			$this->actOnTable($insert);
+		}
+		return parent::insert($insert);
+	}
+
+	public function delete($delete = null, $alias = null) {
+		if (is_string($delete) && $delete) {
+			$this->actOnTable($delete);
+		}
+		return parent::delete($delete, $alias);
+	}
+
+	private function checkJoin(string $table): void {
+		if ($this->shardDefinition) {
+			if ($table === $this->mainTable) {
+				throw new InvalidShardedQueryException("Sharded query on {$this->mainTable} isn't allowed to join on itself");
+			}
+			if (!$this->shardDefinition->hasTable($table)) {
+				// this generally shouldn't happen as the partitioning logic should prevent this
+				// but the check is here just in case
+				throw new InvalidShardedQueryException("Sharded query on {$this->shardDefinition->table} isn't allowed to join on $table");
+			}
+		}
+	}
+
+	public function innerJoin($fromAlias, $join, $alias, $condition = null) {
+		$this->checkJoin($join);
+		return parent::innerJoin($fromAlias, $join, $alias, $condition);
+	}
+
+	public function leftJoin($fromAlias, $join, $alias, $condition = null) {
+		$this->checkJoin($join);
+		return parent::leftJoin($fromAlias, $join, $alias, $condition);
+	}
+
+	public function rightJoin($fromAlias, $join, $alias, $condition = null) {
+		if ($this->shardDefinition) {
+			throw new InvalidShardedQueryException("Sharded query on {$this->shardDefinition->table} isn't allowed to right join");
+		}
+		return parent::rightJoin($fromAlias, $join, $alias, $condition);
+	}
+
+	public function join($fromAlias, $join, $alias, $condition = null) {
+		return $this->innerJoin($fromAlias, $join, $alias, $condition);
+	}
+
+	public function setMaxResults($maxResults) {
+		if ($maxResults > 0) {
+			$this->limit = (int)$maxResults;
+		}
+		return parent::setMaxResults($maxResults);
+	}
+
+	public function setFirstResult($firstResult) {
+		if ($firstResult > 0) {
+			$this->offset = (int)$firstResult;
+		}
+		if ($this->shardDefinition && count($this->shardDefinition->shards) > 1) {
+			// we have to emulate offset
+			return $this;
+		} else {
+			return parent::setFirstResult($firstResult);
+		}
+	}
+
+	public function addOrderBy($sort, $order = null) {
+		$this->registerOrder((string) $sort, (string)$order ?? "ASC");
+		return parent::orderBy($sort, $order);
+	}
+
+	public function orderBy($sort, $order = null) {
+		$this->sortList = [];
+		$this->registerOrder((string) $sort, (string)$order ?? "ASC");
+		return parent::orderBy($sort, $order);
+	}
+
+	private function registerOrder(string $column, string $order): void {
+		// handle `mime + 0` and similar by just sorting on the first part of the expression
+		[$column] = explode(' ', $column);
+		$column = trim($column, '`');
+		$this->sortList[] = [
+			'column' => $column,
+			'order' => strtoupper($order),
+		];
+	}
+
+	public function hintShardKey(string $column, mixed $value) {
+		if ($this->shardDefinition?->isKey($column)) {
+			$this->primaryKeys[] = $value;
+		}
+		if ($column === $this->shardDefinition?->shardKey) {
+			$this->shardKeys[] = $value;
+		}
+		return $this;
+	}
+
+	public function runAcrossAllShards() {
+		$this->allShards = true;
+		return $this;
+	}
+
+	/**
+	 * @throws InvalidShardedQueryException
+	 */
+	public function validate(): void {
+		if ($this->shardDefinition && $this->insertTable) {
+			if ($this->allShards) {
+				throw new InvalidShardedQueryException("Can't insert across all shards");
+			}
+			if (empty($this->getShardKeys())) {
+				throw new InvalidShardedQueryException("Can't insert without shard key");
+			}
+		}
+		if ($this->shardDefinition && !$this->allShards) {
+			if (empty($this->getShardKeys()) && empty($this->getPrimaryKeys())) {
+				throw new InvalidShardedQueryException("No shard key or primary key set for query");
+			}
+		}
+		if ($this->shardDefinition && $this->updateShardKey) {
+			$newShardKey = $this->getKeyValue($this->updateShardKey);
+			$oldShardKeys = $this->getShardKeys();
+			if (count($newShardKey) !== 1) {
+				throw new InvalidShardedQueryException("Can't set shard key to an array");
+			}
+			$newShardKey = current($newShardKey);
+			if (empty($oldShardKeys)) {
+				throw new InvalidShardedQueryException("Can't update without shard key");
+			}
+			$oldShards = array_values(array_unique(array_map(function ($shardKey) {
+				return $this->shardDefinition->getShardForKey((int)$shardKey);
+			}, $oldShardKeys)));
+			$newShard = $this->shardDefinition->getShardForKey((int)$newShardKey);
+			if ($oldShards === [$newShard]) {
+				throw new InvalidShardedQueryException("Update statement would move rows to a different shard");
+			}
+		}
+	}
+
+	public function executeQuery(?IDBConnection $connection = null): IResult {
+		$this->validate();
+		if ($this->shardDefinition) {
+			$runner = new ShardQueryRunner($this->shardConnectionManager, $this->shardDefinition);
+			return $runner->executeQuery($this->builder, $this->allShards, $this->getShardKeys(), $this->getPrimaryKeys(), $this->sortList, $this->limit, $this->offset);
+		}
+		return parent::executeQuery($connection);
+	}
+
+	public function executeStatement(?IDBConnection $connection = null): int {
+		$this->validate();
+		if ($this->shardDefinition) {
+			$runner = new ShardQueryRunner($this->shardConnectionManager, $this->shardDefinition);
+			if ($this->insertTable) {
+				$shards = $runner->getShards($this->allShards, $this->getShardKeys());
+				if (!$shards) {
+					throw new InvalidShardedQueryException("Can't insert without shard key");
+				}
+				$count = 0;
+				foreach ($shards as $shard) {
+					$shardConnection = $this->shardConnectionManager->getConnection($this->shardDefinition, $shard);
+					if (!$this->primaryKeys && $this->shardDefinition->table === $this->insertTable) {
+						$id = $this->autoIncrementHandler->getNextPrimaryKey($this->shardDefinition, $shard);
+						parent::setValue($this->shardDefinition->primaryKey, $this->createParameter('__generated_primary_key'));
+						$this->setParameter('__generated_primary_key', $id, self::PARAM_INT);
+						$this->lastInsertId = $id;
+					}
+					$count += parent::executeStatement($shardConnection);
+
+					$this->lastInsertConnection = $shardConnection;
+				}
+				return $count;
+			} else {
+				return $runner->executeStatement($this->builder, $this->allShards, $this->getShardKeys(), $this->getPrimaryKeys());
+			}
+		}
+		return parent::executeStatement($connection);
+	}
+
+	public function getLastInsertId(): int {
+		if ($this->lastInsertId) {
+			return $this->lastInsertId;
+		}
+		if ($this->lastInsertConnection) {
+			$table = $this->builder->prefixTableName($this->insertTable);
+			return $this->lastInsertConnection->lastInsertId($table);
+		} else {
+			return parent::getLastInsertId();
+		}
+	}
+
+
+}

lib/private/DB/SchemaWrapper.php

@@ -36,6 +36,9 @@ class SchemaWrapper implements ISchemaWrapper {
 	public function performDropTableCalls() {
 		foreach ($this->tablesToDelete as $tableName => $true) {
 			$this->connection->dropTable($tableName);
+			foreach ($this->connection->getShardConnections() as $shardConnection) {
+				$shardConnection->dropTable($tableName);
+			}
 			unset($this->tablesToDelete[$tableName]);
 		}
 	}

lib/private/Files/Cache/Cache.php

@@ -9,6 +9,7 @@ namespace OC\Files\Cache;
 
 use Doctrine\DBAL\Exception\UniqueConstraintViolationException;
 use OC\DB\Exceptions\DbalException;
+use OC\DB\QueryBuilder\Sharded\ShardDefinition;
 use OC\Files\Search\SearchComparison;
 use OC\Files\Search\SearchQuery;
 use OC\Files\Storage\Wrapper\Encryption;
@@ -284,6 +285,7 @@ class Cache implements ICache {
 				if (count($extensionValues)) {
 					$query = $this->getQueryBuilder();
 					$query->insert('filecache_extended');
+					$query->hintShardKey('storage', $storageId);
 
 					$query->setValue('fileid', $query->createNamedParameter($fileId, IQueryBuilder::PARAM_INT));
 					foreach ($extensionValues as $column => $value) {
@@ -357,6 +359,7 @@ class Cache implements ICache {
 			try {
 				$query = $this->getQueryBuilder();
 				$query->insert('filecache_extended');
+				$query->hintShardKey('storage', $this->getNumericStorageId());
 
 				$query->setValue('fileid', $query->createNamedParameter($id, IQueryBuilder::PARAM_INT));
 				foreach ($extensionValues as $column => $value) {
@@ -652,6 +655,15 @@ class Cache implements ICache {
 				throw new \Exception('Invalid source storage path: ' . $sourcePath);
 			}
 
+			$shardDefinition = $this->connection->getShardDefinition('filecache');
+			if (
+				$shardDefinition &&
+				$shardDefinition->getShardForKey($sourceCache->getNumericStorageId()) !== $shardDefinition->getShardForKey($this->getNumericStorageId())
+			) {
+				$this->moveFromStorageSharded($shardDefinition, $sourceCache, $sourceData, $targetPath);
+				return;
+			}
+
 			$sourceId = $sourceData['fileid'];
 			$newParentId = $this->getParentId($targetPath);
 
@@ -673,7 +685,7 @@ class Cache implements ICache {
 
 				$childChunks = array_chunk($childIds, 1000);
 
-				$query = $this->connection->getQueryBuilder();
+				$query = $this->getQueryBuilder();
 
 				$fun = $query->func();
 				$newPathFunction = $fun->concat(
@@ -681,12 +693,15 @@ class Cache implements ICache {
 					$fun->substring('path', $query->createNamedParameter($sourceLength + 1, IQueryBuilder::PARAM_INT))// +1 for the leading slash
 				);
 				$query->update('filecache')
-					->set('storage', $query->createNamedParameter($targetStorageId, IQueryBuilder::PARAM_INT))
 					->set('path_hash', $fun->md5($newPathFunction))
 					->set('path', $newPathFunction)
-					->where($query->expr()->eq('storage', $query->createNamedParameter($sourceStorageId, IQueryBuilder::PARAM_INT)))
+					->whereStorageId($sourceStorageId)
 					->andWhere($query->expr()->in('fileid', $query->createParameter('files')));
 
+				if ($sourceStorageId !== $targetStorageId) {
+					$query->set('storage', $query->createNamedParameter($targetStorageId), IQueryBuilder::PARAM_INT);
+				}
+
 				// when moving from an encrypted storage to a non-encrypted storage remove the `encrypted` mark
 				if ($sourceCache->hasEncryptionWrapper() && !$this->hasEncryptionWrapper()) {
 					$query->set('encrypted', $query->createNamedParameter(0, IQueryBuilder::PARAM_INT));
@@ -728,13 +743,17 @@ class Cache implements ICache {
 
 			$query = $this->getQueryBuilder();
 			$query->update('filecache')
-				->set('storage', $query->createNamedParameter($targetStorageId))
 				->set('path', $query->createNamedParameter($targetPath))
 				->set('path_hash', $query->createNamedParameter(md5($targetPath)))
 				->set('name', $query->createNamedParameter(basename($targetPath)))
 				->set('parent', $query->createNamedParameter($newParentId, IQueryBuilder::PARAM_INT))
+				->whereStorageId($sourceStorageId)
 				->whereFileId($sourceId);
 
+			if ($sourceStorageId !== $targetStorageId) {
+				$query->set('storage', $query->createNamedParameter($targetStorageId), IQueryBuilder::PARAM_INT);
+			}
+
 			// when moving from an encrypted storage to a non-encrypted storage remove the `encrypted` mark
 			if ($sourceCache->hasEncryptionWrapper() && !$this->hasEncryptionWrapper()) {
 				$query->set('encrypted', $query->createNamedParameter(0, IQueryBuilder::PARAM_INT));
@@ -891,6 +910,7 @@ class Cache implements ICache {
 			$query->select($query->func()->count())
 				->from('filecache')
 				->whereParent($fileId)
+				->whereStorageId($this->getNumericStorageId())
 				->andWhere($query->expr()->lt('size', $query->createNamedParameter(0, IQueryBuilder::PARAM_INT)));
 
 			$result = $query->execute();
@@ -1183,4 +1203,72 @@ class Cache implements ICache {
 			return null;
 		}
 	}
+
+	private function moveFromStorageSharded(ShardDefinition $shardDefinition, ICache $sourceCache, ICacheEntry $sourceEntry, $targetPath) {
+		if ($sourceEntry->getMimeType() === ICacheEntry::DIRECTORY_MIMETYPE) {
+			$fileIds = $this->getChildIds($sourceCache->getNumericStorageId(), $sourceEntry->getPath());
+		} else {
+			$fileIds = [];
+		}
+		$fileIds[] = $sourceEntry->getId();
+
+		$helper = $this->connection->getCrossShardMoveHelper();
+
+		$sourceConnection = $helper->getConnection($shardDefinition, $sourceCache->getNumericStorageId());
+		$targetConnection = $helper->getConnection($shardDefinition, $this->getNumericStorageId());
+
+		$cacheItems = $helper->loadItems($sourceConnection, "filecache", "fileid", $fileIds);
+		$extendedItems = $helper->loadItems($sourceConnection, "filecache_extended", "fileid", $fileIds);
+		$metadataItems = $helper->loadItems($sourceConnection, "files_metadata", "file_id", $fileIds);
+
+		// when moving from an encrypted storage to a non-encrypted storage remove the `encrypted` mark
+		$removeEncryptedFlag = ($sourceCache instanceof Cache && $sourceCache->hasEncryptionWrapper()) && !$this->hasEncryptionWrapper();
+
+		$sourcePathLength = strlen($sourceEntry->getPath());
+		foreach ($cacheItems as &$cacheItem) {
+			if ($cacheItem['path'] === $sourceEntry->getPath()) {
+				$cacheItem['path'] = $targetPath;
+				$cacheItem['parent'] = $this->getParentId($targetPath);
+				$cacheItem['name'] = basename($cacheItem['path']);
+			} else {
+				$cacheItem['path'] = $targetPath . '/' . substr($cacheItem['path'], $sourcePathLength + 1); // +1 for the leading slash
+			}
+			$cacheItem['path_hash'] = md5($cacheItem['path']);
+			$cacheItem['storage'] = $this->getNumericStorageId();
+			if ($removeEncryptedFlag) {
+				$cacheItem['encrypted'] = 0;
+			}
+		}
+
+		$targetConnection->beginTransaction();
+
+		try {
+			$helper->saveItems($targetConnection, "filecache", $cacheItems);
+			$helper->saveItems($targetConnection, "filecache_extended", $extendedItems);
+			$helper->saveItems($targetConnection, "files_metadata", $metadataItems);
+		} catch (\Exception $e) {
+			$targetConnection->rollback();
+			throw $e;
+		}
+
+		$sourceConnection->beginTransaction();
+
+		try {
+			$helper->deleteItems($sourceConnection, "filecache", "fileid", $fileIds);
+			$helper->deleteItems($sourceConnection, "filecache_extended", "fileid", $fileIds);
+			$helper->deleteItems($sourceConnection, "files_metadata", "file_id", $fileIds);
+		} catch (\Exception $e) {
+			$targetConnection->rollback();
+			$sourceConnection->rollBack();
+			throw $e;
+		}
+
+		try {
+			$sourceConnection->commit();
+		} catch (\Exception $e) {
+			$targetConnection->rollback();
+			throw $e;
+		}
+		$targetConnection->commit();
+	}
 }

lib/private/Server.php

@@ -811,7 +811,7 @@ class Server extends ServerContainer implements IServerContainer {
 		$this->registerAlias(IDBConnection::class, ConnectionAdapter::class);
 		$this->registerService(Connection::class, function (Server $c) {
 			$systemConfig = $c->get(SystemConfig::class);
-			$factory = new \OC\DB\ConnectionFactory($systemConfig);
+			$factory = new \OC\DB\ConnectionFactory($systemConfig, $c->get(ICacheFactory::class));
 			$type = $systemConfig->getValue('dbtype', 'sqlite');
 			if (!$factory->isValidType($type)) {
 				throw new \OC\DatabaseException('Invalid database type');

lib/public/DB/QueryBuilder/IQueryBuilder.php

@@ -1009,6 +1009,15 @@ interface IQueryBuilder {
 	 */
 	public function getTableName($table);
 
+	/**
+	 * Returns the table name with database prefix as needed by the implementation
+	 *
+	 * @param string $table
+	 * @return string
+	 * @since 30.0.0
+	 */
+	public function prefixTableName(string $table): string;
+
 	/**
 	 * Returns the column name quoted and with table alias prefix as needed by the implementation
 	 *
@@ -1019,6 +1028,24 @@ interface IQueryBuilder {
 	 */
 	public function getColumnName($column, $tableAlias = '');
 
+	/**
+	 * Provide a hint for the shard key for queries where this can't be detected otherwise
+	 *
+	 * @param string $column
+	 * @param mixed $value
+	 * @return $this
+	 * @since 30.0.0
+	 */
+	public function hintShardKey(string $column, mixed $value);
+
+	/**
+	 * Set the query to run across all shards if sharding is enabled.
+	 *
+	 * @return $this
+	 * @since 30.0.0
+	 */
+	public function runAcrossAllShards();
+
 	/**
 	 * Get a list of column names that are expected in the query output
 	 *

lib/public/DB/QueryBuilder/Sharded/IShardMapper.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCP\DB\QueryBuilder\Sharded;
+
+/**
+ * Implementation of logic of mapping shard keys to shards.
+ * @since 30.0.0
+ */
+interface IShardMapper {
+	/**
+	 * Get the shard number for a given shard key and total shard count
+	 *
+	 * @param int $key
+	 * @param int $count
+	 * @return int
+	 * @since 30.0.0
+	 */
+	public function getShardForKey(int $key, int $count): int;
+}

lib/public/IDBConnection.php

@@ -11,6 +11,8 @@
 namespace OCP;
 
 use Doctrine\DBAL\Schema\Schema;
+use OC\DB\QueryBuilder\Sharded\CrossShardMoveHelper;
+use OC\DB\QueryBuilder\Sharded\ShardDefinition;
 use OCP\DB\Exception;
 use OCP\DB\IPreparedStatement;
 use OCP\DB\IResult;
@@ -345,4 +347,21 @@ interface IDBConnection {
 	 * @return self::PLATFORM_MYSQL|self::PLATFORM_ORACLE|self::PLATFORM_POSTGRES|self::PLATFORM_SQLITE
 	 */
 	public function getDatabaseProvider(): string;
+
+	/**
+	 * Get the shard definition by name, if configured
+	 *
+	 * @param string $name
+	 * @return ShardDefinition|null
+	 * @since 30.0.0
+	 */
+	public function getShardDefinition(string $name): ?ShardDefinition;
+
+	/**
+	 * Get a helper class for implementing cross-shard moves
+	 *
+	 * @return CrossShardMoveHelper
+	 * @since 30.0.0
+	 */
+	public function getCrossShardMoveHelper(): CrossShardMoveHelper;
 }

tests/lib/DB/ConnectionFactoryTest.php

@@ -8,6 +8,7 @@ namespace Test\DB;
 
 use OC\DB\ConnectionFactory;
 use OC\SystemConfig;
+use OCP\ICacheFactory;
 use Test\TestCase;
 
 class ConnectionFactoryTest extends TestCase {
@@ -33,7 +34,8 @@ class ConnectionFactoryTest extends TestCase {
 	public function testSplitHostFromPortAndSocket($host, array $expected) {
 		/** @var SystemConfig $config */
 		$config = $this->createMock(SystemConfig::class);
-		$factory = new ConnectionFactory($config);
+		$cacheFactory = $this->createMock(ICacheFactory::class);
+		$factory = new ConnectionFactory($config, $cacheFactory);
 
 		$this->assertEquals($expected, self::invokePrivate($factory, 'splitHostFromPortAndSocket', [$host]));
 	}

tests/lib/DB/QueryBuilder/Partitioned/PartitionedQueryBuilderTest.php

@@ -9,6 +9,9 @@ declare(strict_types=1);
 namespace Test\DB\QueryBuilder\Partitioned;
 
 use OC\DB\QueryBuilder\Partitioned\PartitionedQueryBuilder;
+use OC\DB\QueryBuilder\Partitioned\PartitionSplit;
+use OC\DB\QueryBuilder\Sharded\AutoIncrementHandler;
+use OC\DB\QueryBuilder\Sharded\ShardConnectionManager;
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\IDBConnection;
 use OCP\Server;
@@ -19,9 +22,13 @@ use Test\TestCase;
  */
 class PartitionedQueryBuilderTest extends TestCase {
 	private IDBConnection $connection;
+	private ShardConnectionManager $shardConnectionManager;
+	private AutoIncrementHandler $autoIncrementHandler;
 
 	protected function setUp(): void {
 		$this->connection = Server::get(IDBConnection::class);
+		$this->shardConnectionManager = Server::get(ShardConnectionManager::class);
+		$this->autoIncrementHandler = Server::get(AutoIncrementHandler::class);
 
 		$this->setupFileCache();
 	}
@@ -37,7 +44,7 @@ class PartitionedQueryBuilderTest extends TestCase {
 		if ($builder instanceof PartitionedQueryBuilder) {
 			return $builder;
 		} else {
-			return new PartitionedQueryBuilder($builder);
+			return new PartitionedQueryBuilder($builder, [], $this->shardConnectionManager, $this->autoIncrementHandler);
 		}
 	}
 

tests/lib/DB/QueryBuilder/Sharded/SharedQueryBuilderTest.php

@@ -0,0 +1,125 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2024 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Test\DB\QueryBuilder\Sharded;
+
+use OC\DB\QueryBuilder\Sharded\AutoIncrementHandler;
+use OC\DB\QueryBuilder\Sharded\InvalidShardedQueryException;
+use OC\DB\QueryBuilder\Sharded\RoundRobinShardMapper;
+use OC\DB\QueryBuilder\Sharded\ShardConnectionManager;
+use OC\DB\QueryBuilder\Sharded\ShardDefinition;
+use OC\DB\QueryBuilder\Sharded\ShardedQueryBuilder;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+use OCP\Server;
+use Test\TestCase;
+
+/**
+ * @group DB
+ */
+class SharedQueryBuilderTest extends TestCase {
+	private IDBConnection $connection;
+	private AutoIncrementHandler $autoIncrementHandler;
+
+	protected function setUp(): void {
+		$this->connection = Server::get(IDBConnection::class);
+		$this->autoIncrementHandler = Server::get(AutoIncrementHandler::class);
+	}
+
+
+	private function getQueryBuilder(string $table, string $shardColumn, string $primaryColumn, array $companionTables = []): ShardedQueryBuilder {
+		return new ShardedQueryBuilder(
+			$this->connection->getQueryBuilder(),
+			[
+				new ShardDefinition($table, $primaryColumn, [], $shardColumn, new RoundRobinShardMapper(), $companionTables, []),
+			],
+			$this->createMock(ShardConnectionManager::class),
+			$this->autoIncrementHandler,
+		);
+	}
+
+	public function testGetShardKeySingleParam() {
+		$query = $this->getQueryBuilder('filecache', 'storage', 'fileid');
+		$query->select('fileid', 'path')
+			->from('filecache')
+			->where($query->expr()->eq('storage', $query->createNamedParameter(10, IQueryBuilder::PARAM_INT)));
+
+		$this->assertEquals([], $query->getPrimaryKeys());
+		$this->assertEquals([10], $query->getShardKeys());
+	}
+
+	public function testGetPrimaryKeyParam() {
+		$query = $this->getQueryBuilder('filecache', 'storage', 'fileid');
+		$query->select('fileid', 'path')
+			->from('filecache')
+			->where($query->expr()->in('fileid', $query->createNamedParameter([10, 11], IQueryBuilder::PARAM_INT)));
+
+		$this->assertEquals([10, 11], $query->getPrimaryKeys());
+		$this->assertEquals([], $query->getShardKeys());
+	}
+
+	public function testValidateWithShardKey() {
+		$query = $this->getQueryBuilder('filecache', 'storage', 'fileid');
+		$query->select('fileid', 'path')
+			->from('filecache')
+			->where($query->expr()->eq('storage', $query->createNamedParameter(10)));
+
+		$query->validate();
+		$this->assertTrue(true);
+	}
+
+	public function testValidateWithPrimaryKey() {
+		$query = $this->getQueryBuilder('filecache', 'storage', 'fileid');
+		$query->select('fileid', 'path')
+			->from('filecache')
+			->where($query->expr()->in('fileid', $query->createNamedParameter([10, 11], IQueryBuilder::PARAM_INT)));
+
+		$query->validate();
+		$this->assertTrue(true);
+	}
+
+	public function testValidateWithNoKey() {
+		$query = $this->getQueryBuilder('filecache', 'storage', 'fileid');
+		$query->select('fileid', 'path')
+			->from('filecache')
+			->where($query->expr()->lt('size', $query->createNamedParameter(0)));
+
+		$this->expectException(InvalidShardedQueryException::class);
+		$query->validate();
+		$this->fail("exception expected");
+	}
+
+	public function testValidateNonSharedTable() {
+		$query = $this->getQueryBuilder('filecache', 'storage', 'fileid');
+		$query->select('configvalue')
+			->from('appconfig')
+			->where($query->expr()->eq('configkey', $query->createNamedParameter('test')));
+
+		$query->validate();
+		$this->assertTrue(true);
+	}
+
+	public function testGetShardKeyMultipleSingleParam() {
+		$query = $this->getQueryBuilder('filecache', 'storage', 'fileid');
+		$query->select('fileid', 'path')
+			->from('filecache')
+			->where($query->expr()->andX(
+				$query->expr()->gt('mtime', $query->createNamedParameter(0), IQueryBuilder::PARAM_INT),
+				$query->expr()->orX(
+					$query->expr()->eq('storage', $query->createNamedParameter(10, IQueryBuilder::PARAM_INT)),
+					$query->expr()->andX(
+						$query->expr()->eq('storage', $query->createNamedParameter(11, IQueryBuilder::PARAM_INT)),
+						$query->expr()->like('path', $query->createNamedParameter("foo/%"))
+					)
+				)
+			));
+
+		$this->assertEquals([], $query->getPrimaryKeys());
+		$this->assertEquals([10, 11], $query->getShardKeys());
+	}
+}

tests/lib/Files/Cache/CacheTest.php

@@ -483,6 +483,23 @@ class CacheTest extends \Test\TestCase {
 		}
 	}
 
+	public function testMoveFromCache() {
+		$data = ['size' => 100, 'mtime' => 50, 'mimetype' => 'foo/bar'];
+		$folderData = ['size' => 100, 'mtime' => 50, 'mimetype' => 'httpd/unix-directory'];
+
+		$this->cache2->put("folder", $folderData);
+		$this->cache2->put("folder/sub", $data);
+
+
+		$this->cache->moveFromCache($this->cache2, "folder", "targetfolder");
+
+		$this->assertFalse($this->cache2->inCache("folder"));
+		$this->assertFalse($this->cache2->inCache("folder/sub"));
+
+		$this->assertTrue($this->cache->inCache("targetfolder"));
+		$this->assertTrue($this->cache->inCache("targetfolder/sub"));
+	}
+
 	public function testGetIncomplete() {
 		$file1 = 'folder1';
 		$file2 = 'folder2';

tests/lib/TestCase.php

@@ -342,6 +342,7 @@ abstract class TestCase extends \PHPUnit\Framework\TestCase {
 	 */
 	protected static function tearDownAfterClassCleanFileCache(IQueryBuilder $queryBuilder) {
 		$queryBuilder->delete('filecache')
+			->runAcrossAllShards()
 			->execute();
 	}