06ce976370
In these changes, we pair draining the view builder with its start.
To better understand what was done and why, let's first look at the
situation before this commit and the context of it:
(a) The following things happened in order:
1. The view builder would be constructed.
2. Right after that, a deferred lambda would be created to stop the
view builder during shutdown.
3. group0_service would be started.
4. A deferred lambda stopping group0_service would be created right
after that.
5. The view builder would be started.
(b) Because the view builder depends on group0_client, it couldn't be
started before starting group0_service. On the other hand, other
services depend on the view builder, e.g. the stream manager. That
makes changing the order of initialization a difficult problem,
so we want to avoid doing that unless we're sure it's the right
choice.
(c) Since the view builder uses group0_client, there was a possibility
of running into a segmentation fault issue in the following
scenario:
1. A call to `view_builder::mark_view_build_success()` is issued.
2. We stop group0_service.
3. `view_builder::mark_view_build_success()` calls
`announce_with_raft()`, which leads to a use-after-free because
group0_service has already been destroyed.
This very scenario took place in scylladb/scylladb#20772.
Initially, we decided to solve the issue by initializing
group0_service a bit earlier (scylladb/scylladb@7bad8378c7).
Unfortunately, it led to other issues described in scylladb/scylladb#21534.
We reverted that change in the previous commit. These changes are the
second attempt to the problem where we want to solve it in a safer manner.
The solution we came up with is to pair the start of the view builder
with a deferred lambda that deinitializes it by calling
`view_builder::drain()`. No other component of the system should be
able to use the view builder anymore, so it's safe to do that.
Furthermore, that pairing makes the analysis of
initialization/deinitialization order much easier. We also solve the
aformentioned use-after-free issue because the view builder itself
will no longer attempt to use group0_client.
Note that we still pair a deferred lambda calling `view_builder::stop()`
with the construction of the view builder; that function will also call
`view_builder::drain()`. Another notable thing is `view_builder::drain()`
may be called earlier by `storage_service::do_drain()`. In other words,
these changes cover the situation when Scylla runs into a problem when
starting up.
Fixes scylladb/scylladb#20772
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.