CatDb is a high-performance ordered key-value database for .NET, built around the Waterfall Tree (WTree): https://ieeexplore.ieee.org/document/6857846.
CatDb started from STSdb4, but this project has evolved substantially and now differs significantly in architecture, behavior, and public API.
CatDb is server-first. Run it as a dedicated service via CatDb.Server (ASP.NET Core with HTTP/TCP APIs), or link it as a library directly into your .NET process. Both use the same high-performance engine.
| Package | Description | Version |
|---|---|---|
| CatDb | Database engine library |
- Server or in-process: run as a service or link directly into your process.
- Ordered key storage with efficient forward/backward/range scans.
- Write-optimized WTree internals for heavy mixed workloads.
- Secondary index support in the public API.
- Fluent query builders for key and index queries.
- Supports non-primitive keys/fields (including composite/object types with comparers).
Server-first: connect to a running CatDb.Server/TCP server (one connection string covers Network, File, or Memory — see Database engine):
using CatDb.Database;
using var engine = CatDb.Database.CatDb.FromConnectionString(
"Provider=Network;Host=localhost;Port=7182;Database=default;User Id=admin;Password=admin");
var users = engine.OpenXTable<long, User>("users");
users[1] = new User("ada@example.com", "Ada", "London");
users[2] = new User("grace@example.com", "Grace", "New York");
engine.Commit();
if (users.TryGet(1, out var user))
Console.WriteLine($"{user.Email} / {user.City}");
public sealed record User(string Email, string Name, string City);No server needed: swap the engine for a local file or in-memory store — same table API either way.
using var engine = CatDb.Database.CatDb.FromFile("app.catdb"); // or FromMemory() / FromStream(stream)using CatDb.Extensions;
// Primary key query
var page = users.Query().AtLeast(1).Take(100).ToList();
// Descending query
var last10 = users.Query().Backward().Take(10).ToList();using CatDb.Database.Indexing;
using CatDb.Extensions;
users.CreateIndex("Email", x => x.Email, IndexType.Unique);
users.CreateIndex("City", x => x.City, IndexType.NonUnique);
var byEmail = users.Query(x => x.Email).Equals("ada@example.com").FirstOrDefault();
var london = users.Query(x => x.City).Equals("London").Take(20).ToList();
var londonCount = users.Query(x => x.City).Equals("London").Count();dotnet build --no-incremental
dotnet test --no-build
dotnet run --project examples/CatDb.GettingStartedOptional stress run:
cd examples/CatDb.StressTest
dotnet run -c Release -- --duration 120Background paper on Waterfall Tree concepts: https://ieeexplore.ieee.org/document/6857846/references
MIT License — Copyright (c) 2024-2026 CatDb. See LICENSE for full text.
Free to use in personal, commercial, and proprietary projects.