753e2d3c57
When we upgrade a cluster to use Raft, or perform manual Raft recovery procedure (which also creates a fresh group 0 cluster, using the same algorithm as during upgrade), we start with a non-empty group 0 state machine; in particular, the schema tables are non-empty. In this case we need to ensure that nodes which join group 0 receive the group 0 state. Right now this is not the case. In previous releases, where group 0 consisted only of schema, and schema pulls were also done outside Raft, those nodes received schema through this outside mechanism. In91f609d065we disabled schema pulls outside Raft; we're also extending group 0 with other things, like topology-specific state. To solve this, we force snapshot transfers by setting the initial snapshot index on the first group 0 server to `1` instead of `0`. During replication, Raft will see that the joining servers are behind, triggering snapshot transfer and forcing them to pull group 0 state. It's unnecessary to do this for cluster which bootstraps with Raft enabled right away but it also doesn't hurt, so we keep the logic simple and don't introduce branches based on that. Extend Raft upgrade tests with a node bootstrap step at the end to prevent regressions (without this patch, the step would hang - node would never join, waiting for schema). Fixes: #14066 Closes #14336 (cherry picked from commitff386e7a44) Backport note: contrary to the claims above, it turns out that it is actually necessary to create snapshots in clusters which bootstrap with Raft, because of tombstones in current schema state expire hence applying schema mutations from old Raft log entries is not really idempotent. Snapshot transfer, which transfers group 0 history and state_ids, prevents old entries from applying schema mutations over latest schema state. Ref: scylladb/scylladb#16683
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++20 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 APIs - CQL and Thrift. 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 users mailing list and Slack channel are for users to discuss configuration, management, and operations of the ScyllaDB open source.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.