c1c0c96643
service_levels: self-heal stale v1 marker after raft topology upgrade This PR handles an upgrade corner case where a node may already be using raft topology, while `system.scylla_local` still marks service levels as v1. The problem was introduced by commit2917ec5d51("service:qos: service levels migration"), which added the service-levels migration from `system_distributed.service_levels` to `system.service_levels_v2` as part of the raft topology upgrade. However, if the cluster had no service levels configured, there was no data to migrate. In that case, the migration path could leave the local version marker unchanged, so the node would later observe an inconsistent state: * raft topology is already enabled; * service levels are still marked as v1 in `system.scylla_local`. Such clusters can be left in a stale state and fail startup during upgrade to 2026.2 This PR makes the upgrade path self-healing. The first commit restores `service_level_controller::migrate_to_v2()`, giving us a group0-based path for writing the service-levels v2 state even after raft topology is already in use. The second commit wires this path into startup. When the node detects the stale raft-topology + service-levels-v1 state, it retries the migration a bounded number of times and updates the version marker to v2 instead of failing startup. With this change, clusters that were left in this stale state can recover automatically during upgrade to 2026. Fixes: SCYLLADB-2038 backport: 2026.2 2026.1 we need this functionality when we are upgrading older servers - (cherry picked from commitac0a19aab8) - (cherry picked from commitc2014f7e50) - (cherry picked from commit6188bf3e01) Parent PR: #29749 Closes scylladb/scylladb#29905 * github.com:scylladb/scylladb: test/auth_cluster: simulate v1 state in self-heal test When skip_service_levels_v2_initialization is used, write an explicit v1 service level version marker while skipping v2 initialization. This lets the restart test exercise self-healing from v1 to v2. qos: self-heal stale service levels version on startup qos: reintroduce service levels v2 migration self-heal
Scylla
What is Scylla?
Scylla is the real-time big data database that is API-compatible with Apache Cassandra and Amazon DynamoDB. Scylla embraces a shared-nothing approach that increases throughput and storage capacity to realize order-of-magnitude performance improvements and reduce hardware costs.
For more information, please see the ScyllaDB web site.
Build Prerequisites
Scylla is fairly fussy about its build environment, requiring very recent versions of the C++23 compiler and of many libraries to build. The document HACKING.md includes detailed information on building and developing Scylla, but to get Scylla building quickly on (almost) any build machine, Scylla offers a frozen toolchain. This is a pre-configured Docker image which includes recent versions of all the required compilers, libraries and build tools. Using the frozen toolchain allows you to avoid changing anything in your build machine to meet Scylla's requirements - you just need to meet the frozen toolchain's prerequisites (mostly, Docker or Podman being available).
Building Scylla
Building Scylla with the frozen toolchain dbuild is as easy as:
$ git submodule update --init --force --recursive
$ ./tools/toolchain/dbuild ./configure.py
$ ./tools/toolchain/dbuild ninja build/release/scylla
For further information, please see:
- Developer documentation for more information on building Scylla.
- Build documentation on how to build Scylla binaries, tests, and packages.
- Docker image build documentation for information on how to build Docker images.
Running Scylla
To start Scylla server, run:
$ ./tools/toolchain/dbuild ./build/release/scylla --workdir tmp --smp 1 --developer-mode 1
This will start a Scylla node with one CPU core allocated to it and data files stored in the tmp directory.
The --developer-mode is needed to disable the various checks Scylla performs at startup to ensure the machine is configured for maximum performance (not relevant on development workstations).
Please note that you need to run Scylla with dbuild if you built it with the frozen toolchain.
For more run options, run:
$ ./tools/toolchain/dbuild ./build/release/scylla --help
Testing
See test.py manual.
Scylla APIs and compatibility
By default, Scylla is compatible with Apache Cassandra and its API - CQL. There is also support for the API of Amazon DynamoDB™, which needs to be enabled and configured in order to be used. For more information on how to enable the DynamoDB™ API in Scylla, and the current compatibility of this feature as well as Scylla-specific extensions, see Alternator and Getting started with Alternator.
Documentation
Documentation can be found here. Seastar documentation can be found here. User documentation can be found here.
Training
Training material and online courses can be found at Scylla University. The courses are free, self-paced and include hands-on examples. They cover a variety of topics including Scylla data modeling, administration, architecture, basic NoSQL concepts, using drivers for application development, Scylla setup, failover, compactions, multi-datacenters and how Scylla integrates with third-party applications.
Contributing to Scylla
If you want to report a bug or submit a pull request or a patch, please read the contribution guidelines.
If you are a developer working on Scylla, please read the developer guidelines.
Contact
- The community forum and Slack channel are for users to discuss configuration, management, and operations of ScyllaDB.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.