ce0ed29ad6
This allows the user of `raft::server` to cause it to create a snapshot and truncate the Raft log (leaving no trailing entries; in the future we may extend the API to specify number of trailing entries left if needed). In a later commit we'll add a REST endpoint to Scylla to trigger group 0 snapshots. One use case for this API is to create group 0 snapshots in Scylla deployments which upgraded to Raft in version 5.2 and started with an empty Raft log with no snapshot at the beginning. This causes problems, e.g. when a new node bootstraps to the cluster, it will not receive a snapshot that would contain both schema and group 0 history, which would then lead to inconsistent schema state and trigger assertion failures as observed in scylladb/scylladb#16683. In 5.4 the logic of initial group 0 setup was changed to start the Raft log with a snapshot at index 1 (ff386e7a44) but a problem remains with these existing deployments coming from 5.2, we need a way to trigger a snapshot in them (other than performing 1000 arbitrary schema changes). Another potential use case in the future would be to trigger snapshots based on external memory pressure in tablet Raft groups (for strongly consistent tables). The PR adds the API to `raft::server` and a HTTP endpoint that uses it. In a follow-up PR, we plan to modify group 0 server startup logic to automatically call this API if it sees that no snapshot is present yet (to automatically fix the aforementioned 5.2 deployments once they upgrade.) Closes scylladb/scylladb#16816 * github.com:scylladb/scylladb: raft: remove `empty()` from `fsm_output` test: add test for manual triggering of Raft snapshots api: add HTTP endpoint to trigger Raft snapshots raft: server: add `trigger_snapshot` API raft: server: track last persisted snapshot descriptor index raft: server: framework for handling server requests raft: server: inline `poll_fsm_output` raft: server: fix indentation raft: server: move `io_fiber`'s processing of `batch` to a separate function raft: move `poll_output()` from `fsm` to `server` raft: move `_sm_events` from `fsm` to `server` raft: fsm: remove constructor used only in tests raft: fsm: move trace message from `poll_output` to `has_output` raft: fsm: extract `has_output()` raft: pass `max_trailing_entries` through `fsm_output` to `store_snapshot_descriptor` raft: server: pass `*_aborted` to `set_exception` call (cherry picked from commitd202d32f81) Backport notes: - `has_output()` has a smaller condition in the backported version (because the condition was smaller in `poll_output()`) - `process_fsm_output` has a smaller body (because `io_fiber` had a smaller body) in the backported version - the HTTP API is only started if `raft_group_registry` is started
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.