ade15ad74a
Broadcasts all mutations returned from `prepare_new_cdc_generation_data` except the last one. Each mutation is sent in separate raft command. It takes `group0_guard`, and if the number of mutations is greater than one, the guard is dropped, and a new one is created and returned, otherwise the old one will be returned. Commands are sent in parallel and unguarded (the guard used for sending the last mutation will guarantee that the term hasn't been changed). Returns the generation's UUID, guard and last mutation, which will be sent with additional topology data by the caller. If we send the last mutation in the `write_mutation` command, we would use a total of `n + 1` commands instead of `n-1 + 1` (where `n` is the number of mutations), so it's better to send it in `topology_change` (we need to send it after all `write_mutations`) with some small metadata. With the default commitlog segment size, `mutation_size_threshold` will be 4 MB. In large clusters e.g. 100 nodes, 64 shards per node, 256 vnodes cdc generation data can reach the size of 30 MB, thus there will be no more than 8 commands. In a multi-DC cluster with 100ms latencies between DCs, this operation should take about 200ms since we send the commands concurrently, but even if the commands were replicated sequentially by Raft, it should take no more than 1.6s, which is incomparably smaller than bootstrapping operation (bootstrapping is quick if there is no data in the cluster, but usually if one has 100 nodes they have tons of data, so indeed streaming/repair will take much longer (hours/days)). Fixes FIXME in pr #13683.
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.