1704d7e4f0
The feature check in `enable_features_on_startup` loads the list of features that were enabled previously, goes over every one of them and checks whether each feature is considered supported and whether there is a corresponding `gms::feature` object for it (i.e. the feature is "registered"). The second part of the check is unnecessary and wrong. A feature can be marked as supported but its `gms::feature` object not be present anymore: after a feature is supported for long enough (i.e. we only support upgrades from versions that support the feature), we can consider such a feature to be deprecated. When a feature is deprecated, its `gms::feature` object is removed and the feature is always considered enabled which allows to remove some legacy code. We still consider this feature to be supported and advertise it in gossip, for the sake of the old nodes which, even though they always support the feature, they still check whether other nodes support it. The problem with the check as it is now is that it disallows moving features to the disabled list. If one tries to do it, they will find out that upgrading the node to the new version does not work: `enable_features_on_startup` will load the feature, notice that it is not "registered" (there is no `gms::feature` object for it) and fail to boot. This commit fixes the problem by modifying `enable_features_on_startup` not to look at the registered features list at all. In addition to this, some other small cleanups are performed: - "LARGE_COLLECTION_DETECTION" is removed from the deprecated features list. For some reason, it was put there when the feature was being introduced. It does not break anything because there is a `gms::feature` object for it, but it's slightly confusing and therefore is removed. - The comment in `supported_feature_set` that invites developers to add features there as they are introduced is removed. It is no longer necessary to do so because registered features are put there automatically. Deprecated features should still be put there, as indicated as another comment. Fortunately, this issue does not break any upgrades as of now - since we added enabled cluster feature persisting, no features were deprecated, and we only add registered features to the persisted feature list.
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 community forum 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.