c05be27e4a
In scylladb/scylladb@7301a96, in the function `hint_endpoint_manager::store_hint()`, we transformed the lambda passed to `seastar::with_gate()` to a coroutine lambda to improve the readability. However, there was a subtle problem related to lifetimes of the captures that needed to be addressed: * Since we started `co_await`ing in the lambda, the captures were at risk of being destructed too soon. The usual solution is to wrap a coroutine lambda within a `seastar::coroutine::lambda` object and rely on the extended lifetime enforced by the semantics of the language. See `docs/dev/lambda-coroutine-fiasco.md` for more context. * However, since we don't immediately `co_await` the future returned by `with_gate()`, we cannot rely on the extended lifetime provided by the wrapper. The document linked in the previous bullet point suggests keeping the passed coroutine lambda as a variable and pass it as a reference to `with_gate()`. However, that's not feasible either because we discard the returned future and the function returns almost instantly -- destructing every local object, which would encompass the lambda too. The solution used in the commit was to move captures of the lambda into the lambda's body. That helped because Seastar's backend is responsible for keeping all of the local variables alive until the lambda finishes its execution. However, we didn't move all of the captures into the lambda -- the missing one was the `this` pointer that was implicitly used in the lambda. Address sanitiser hasn't reported any bugs related to the pointer yet, but the bug is most likely there. In this commit, we transform the lambda's body into a new member function and only call it from the lambda. This way, we don't need to care about the lifetimes of the captures because Seastar ensures that the function's arguments stay alive until the coroutine finishes. Choosing this solution instead of assigning `this` to a pointer variable inside the lambda's body and using it to refer to the object's members has actual benefit: it's not possible to accidentally forget to refer to a member of the object via the pointer; it also makes the code less awkward. Fixes scylladb/scylladb#20306 Closes scylladb/scylladb#20258 * github.com:scylladb/scylladb: db/hints: Fix indentation in `do_store_hint()` db/hints: Move code for writing hints to separate function
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++23 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 API - CQL. 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.