7d35cf8657
We want to disable `migration_manager` schema pulls and make schema managed only by Raft group 0 if Raft is enabled. This will be important with Raft-based topology, when schema will depend on topology (e.g. for tablets). We solved the problem partially in PR #13695. However, it's still possible for a bootstrapping node to pull schema in the early part of bootstrap procedure, before it setups group 0, because of how the currently used `_raft_gr.using_raft()` check is implemented. Here's the list of cases: - If a node is bootstrapping in non-Raft mode, schema pulls must remain enabled. - If a node is bootstrapping in Raft mode, it should never perform a schema pull. - If a bootstrapped node is restarting in non-Raft mode but with Raft feature enabled (which means we should start upgrading to use Raft), or restarting in the middle of Raft upgrade procedure, schema pulls must remain enabled until the Raft upgrade procedure finishes. This is also the case of restarting after RECOVERY. - If a bootstrapped node is restarting in Raft mode, it should never perform a schema pull. The `raft_group0` service is responsible for setting up Raft during boot and for the Raft upgrade procedure. So this is the most natural place to make the decision that schema pulls should be disabled. Instead of trying to come up with a correct condition that fully covers the above list of cases, store a `bool` inside `migration_manager` and set it from `raft_group0` function at the right moment - when we decide that we should boot in Raft mode, or restart with Raft, or upgrade. Most of the conditions are already checked in `setup_group0_if_exist`, we just need to set the bool. Also print a log message when schema pulls are disabled. Fix a small bug in `migration_manager::get_schema_for_write` - it was possible for the function to mark schema as synced without actually syncing it if it was running concurrently to the Raft upgrade procedure. Correct some typos in comments and update the comments. Fixes #12870 Closes #14428 * github.com:scylladb/scylladb: raft_group_registry: remove `has_group0()` raft_group0_client: remove `using_raft()` migration_manager: disable schema pulls when schema is Raft-managed
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.