diff --git a/src/db.zig b/src/db.zig
new file mode 100644
index 0000000..5e825a7
--- /dev/null
+++ b/src/db.zig
@@ -0,0 +1,139 @@
+const std = @import("std");
+const encode = @import("encode.zig");
+const memtable = @import("memtable.zig");
+const sstable = @import("sstable.zig");
+const cache = @import("cache.zig");
+const statsmod = @import("stats.zig");
+const Wal = @import("wal.zig").Wal;
+
+const Allocator = std.mem.Allocator;
+const Kind = encode.Kind;
+const Record = encode.Record;
+const Memtable = memtable.Memtable;
+const Reader = sstable.Reader;
+const Builder = sstable.Builder;
+const BlockCache = cache.BlockCache;
+
+pub const WriteBatch = @import("batch.zig").WriteBatch;
+pub const Stats = statsmod.Stats;
+
+fn order(a: []const u8, b: []const u8) std.math.Order {
+    return std.mem.order(u8, a, b);
+}
+
+const walName = "wal.log";
+const manifestName = "MANIFEST";
+
+pub const Options = struct {
+    flushThreshold: usize = 4 * 1024 * 1024,
+    blockCacheBytes: usize = 8 * 1024 * 1024,
+    l0CompactionTrigger: usize = 4,
+    l1BaseBytes: usize = 8 * 1024 * 1024,
+    levelMultiplier: usize = 10,
+    sstableTargetBytes: usize = 2 * 1024 * 1024,
+};
+
+pub const Entry = struct {
+    key: []const u8,
+    value: []const u8,
+};
+
+pub const Db = struct {
+    allocator: Allocator,
+    dir: std.fs.Dir,
+    dirPath: []u8,
+    memtable: Memtable,
+    wal: Wal,
+    sstables: std.ArrayList(*Reader),
+    blockCache: BlockCache,
+    nextFileId: u64,
+    nextSeq: u64,
+    flushThreshold: usize,
+    l0Trigger: usize,
+    l1BaseBytes: usize,
+    levelMultiplier: usize,
+    sstableTargetBytes: usize,
+
+    pub fn open(allocator: Allocator, dirPath: []const u8, options: Options) !Db {
+        try std.fs.cwd().makePath(dirPath);
+        var dir = try std.fs.cwd().openDir(dirPath, .{ .iterate = true });
+        errdefer dir.close();
+
+        var sstables = std.ArrayList(*Reader).init(allocator);
+        errdefer {
+            for (sstables.items) |reader| {
+                reader.deinit();
+                allocator.destroy(reader);
+            }
+            sstables.deinit();
+        }
+
+        var ids = std.ArrayList(u64).init(allocator);
+        defer ids.deinit();
+        var walker = dir.iterate();
+        while (try walker.next()) |item| {
+            if (item.kind != .file) continue;
+            if (parseSstId(item.name)) |id| try ids.append(id);
+        }
+        std.mem.sort(u64, ids.items, {}, std.sort.desc(u64));
+
+        var maxSeq: u64 = 0;
+        var maxId: u64 = 0;
+        for (ids.items) |id| {
+            var nameBuf: [64]u8 = undefined;
+            const name = try sstName(&nameBuf, id);
+            const reader = try allocator.create(Reader);
+            errdefer allocator.destroy(reader);
+            reader.* = try Reader.open(allocator, dir, name, id);
+            errdefer reader.deinit();
+            try sstables.append(reader);
+            if (reader.maxSeq > maxSeq) maxSeq = reader.maxSeq;
+            if (id > maxId) maxId = id;
+        }
+
+        var levelMap = try loadManifest(allocator, dir);
+        defer levelMap.deinit();
+        for (sstables.items) |reader| {
+            reader.level = levelMap.get(reader.fileId) orelse 0;
+        }
+
+        var table = try Memtable.init(allocator);
+        errdefer table.deinit();
+        var wal = try Wal.open(allocator, dir, walName);
+        errdefer wal.close();
+        const walMaxSeq = try wal.replay(&table);
+        if (walMaxSeq > maxSeq) maxSeq = walMaxSeq;
+
+        const dirPathCopy = try allocator.dupe(u8, dirPath);
+
+        return .{
+            .allocator = allocator,
+            .dir = dir,
+            .dirPath = dirPathCopy,
+            .memtable = table,
+            .wal = wal,
+            .sstables = sstables,
+            .blockCache = BlockCache.init(allocator, options.blockCacheBytes),
+            .nextFileId = maxId + 1,
+            .nextSeq = maxSeq + 1,
+            .flushThreshold = options.flushThreshold,
+            .l0Trigger = options.l0CompactionTrigger,
+            .l1BaseBytes = options.l1BaseBytes,
+            .levelMultiplier = options.levelMultiplier,
+            .sstableTargetBytes = options.sstableTargetBytes,
+        };
+    }
+
+    pub fn close(self: *Db) void {
+        self.wal.close();
+        for (self.sstables.items) |reader| {
+            reader.deinit();
+            self.allocator.destroy(reader);
+        }
+        self.sstables.deinit();
+        self.blockCache.deinit();
+        self.memtable.deinit();
+        self.dir.close();
+        self.allocator.free(self.dirPath);
+    }
+