d8fab2a01a
The previous patch introduced a function make_streamed_with_extra_array
which was a duplicate of the existing make_streamed. Reviewers
complained how baroque the new function is (just like the old function),
having to jump through hoops to return a copyable function working
on non-copyable objects, making strange-named copies and shared pointers
of everything.
We needed to return a copyable function (std::function) just because
Alternator used Seastar's json::json_return_type in the return type
from executor function (request_return_type). This json_return_type
contained either a sstring or an std::function, but neither was ever
really appropriate:
1. We want to return noncopyable_function, not an std::function!
2. We want to return an std::string (which rjson::print()) returns,
not an sstring!
So in this patch we stop using seastar::json::json_return_type
entirely in Alternator.
Alternator's request_return_type is now an std::variant of *three* types:
1. std::string for short responses,
2. noncopyable_function for long streamed response
3. api_error for errors.
The ugliest parts of make_streamed() where we made copies and shared
pointers to allow for a copyable function are all gone. Even nicer, a
lot of other ugly relics of using seastar::json_return_type are gone:
1. We no longer need obscure classes and functions like make_jsonable()
and json_string() to convert strings to response bodies - an operation
can simply return a string directly - usually returning
rjson::print(value) or a fixed string like "" and it just works.
2. There is no more usage of seastar::json in Alternator (except one
minor use of seastar::json::formatter::to_json in streams.cc that
can be removed later). Alternator uses RapidJSON for its JSON
needs, we don't need to use random pieces from a different JSON
library.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
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 ScyllaDB.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.