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This series contains an initial implementation of raft persistency module that uses `raft` system table as the underlying storage model. "system.raft" table will be used as a backend storage for implementing raft persistence module in Scylla. It combines both raft log, persisted vote and term, and snapshot info. The table is partitioned by group id, thus allowing multi-raft operation. The rest of the table structure mirrors the fields of corresponding core raft structures defined in `raft.hh`, such as `raft::log_entry`. The raft table stores the only the latest snapshot id while the actual snapshot will be available in a separate table called `system.raft_snapshots`. The schema of `raft_snapshots` mirrors the fields of `raft::snapshot` structure. IDL definitions are also added for every raft struct so that we automatically provide serialization and deserialization facilities needed both for persistency module and for future RPC implmementation. The first patch is a side-change needed to provide complete serialization/deserialization for `bytes_ostream`, which we need when persisting the raft log in the table (since `data` is a variant containing `raft::command` (aka `bytes_ostream`) among others). `bytes_ostream` was lacking `deserialize` function, which is added in the patch. The second patch provides serializer for `lw_shared_ptr<T>` which will be used for `raft::append_entries`, which has a field with `std::vector<const lw_shared_ptr<raft::log_entry>>` type. There is also a patch to extend `fragmented_temporary_buffer` with a static function `allocate_to_fit` that allocates an instance of the fragmented buffer that has a specified size. Individual fragment size is limited to 128kb. The patch-set also contains the test suite covering basic functionality of the persistency module. * manmanson/raft-api-impl-v11: raft/sys_table_storage: add basic tests for raft_sys_table_storage raft: introduce `raft_sys_table_storage` class utils: add `fragmented_temporary_buffer::allocate_to_fit` raft: add IDL definitions for raft types raft: create `system.raft` and `system.raft_snapshots` tables serializer: add `serializer<lw_shared_ptr<T>>` specialization serializer: add `deserialize` function overload for `bytes_ostream`
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.