1 files changed, 66 insertions, 0 deletions
diff --git a/lib/private/DB/QueryBuilder/Sharded/ShardDefinition.php b/lib/private/DB/QueryBuilder/Sharded/ShardDefinition.php
new file mode 100644
index 00000000000..5661ca079e1
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+++ b/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);
+	}
+}