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The AppendReg state machine stores a sequence of integers. It supports `append` inputs which append a single integer to the sequence and return the previous state (before appending). The implementation uses the `append_seq` data structure representing an immutable sequence that uses a vector underneath which may be shared by multiple instances of `append_seq`. Appending to the sequence appends to the underlying vector, but there is no observable effect on the other instances since they use only the prefix of the sequence that wasn't changed. If two instances sharing the same vector try to append, the later one must perform a copy. This allows efficient appends if only one instance is appending, which is useful in the following context: - a Raft server stores a copy in the underlying state machine replica and appends to it, - clients send append operations to the server; the server returns the state of the sequence before it was appended to, - thanks to the sharing, we don't need to copy all elements when returning the sequence to the client, and only one instance (the server) is appending to the shared vector, - summarizing, all operations have amortized O(1) complexity. We use AppendReg instead of ExReg in `basic_generator_test` with a generator which generates a sequence of append operations with unique integers. This implies that the result of every operation uniquely identifies the operation (since it contains the appended integer, and different operations use different integers) and all operations that must have happened before it (since it contains the previous state of the append register), which allows us to reconstruct the "current state" of the register according to the results of operations coming from Raft calls, giving us an on-line serializability checker with O(1) amortized complexity on each operation completion. We also enforce linearizability by checking that every completed operation was previously invoked. We also perform a simple liveness check at the end of the test by ensuring that a leader becomes eventually elected and that we can successfully execute a call. * kbr/linearizability-v2: test: raft: randomized_nemesis_test: check consistency and liveness in basic_generator_test test: raft: randomized_nemesis_test: introduce append register
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.