67b24859bc
~~~
generic_server: convert connection tracking to seastar::gate
If we call server::stop() right after "server" construction, it hangs:
With the server never listening (never accepting connections and never
serving connections), nothing ever calls server::maybe_stop().
Consequently,
co_await _all_connections_stopped.get_future();
at the end of server::stop() deadlocks.
Such a server::stop() call does occur in controller::do_start_server()
[transport/controller.cc], when
- cserver->start() (sharded<cql_server>::start()) constructs a
"server"-derived object,
- start_listening_on_tcp_sockets() throws an exception before reaching
listen_on_all_shards() (for example because it fails to set up client
encryption -- certificate file is inaccessible etc.),
- the "deferred_action"
cserver->stop().get();
is invoked during cleanup.
(The cserver->stop() call exposing the connection tracking problem dates
back to commit ae4d5a60ca ("transport::controller: Shut down distributed
object on startup exception", 2020-11-25), and it's been triggerable
through the above code path since commit 6b178f9a4a
("transport/controller: split configuring sockets into separate
functions", 2024-02-05).)
Tracking live connections and connection acceptances seems like a good fit
for "seastar::gate", so rewrite the tracking with that. "seastar::gate"
can be closed (and the returned future can be waited for) without anyone
ever having entered the gate.
NOTE: this change makes it quite clear that neither server::stop() nor
server::shutdown() must be called multiple times. The permitted sequences
are:
- server::shutdown() + server::stop()
- or just server::stop().
Fixes #10305
Signed-off-by: Laszlo Ersek <laszlo.ersek@scylladb.com>
~~~
Fixes #10305.
I think we might want to backport this -- it fixes a hang-on-misconfiguration which affects `scylla-6.1.0-0.20240804.abbf0b24a60c.x86_64` minimally. Basically every release that contains commit ae4d5a60ca has a theoretical chance for the hang, and every release that contains commit 6b178f9a4a has a practical chance for the hang.
Focusing on the more practical symptom (i.e., releases containing commit 6b178f9a4a), `git tag --contains 6b178f9a4a90` gives us (ignoring candidates and release candidates):
- scylla-6.0.0
- scylla-6.0.1
- scylla-6.0.2
- scylla-6.1.0
Closes scylladb/scylladb#20212
* github.com:scylladb/scylladb:
generic_server: make server::stop() idempotent
generic_server: coroutinize server::shutdown()
generic_server: make server::shutdown() idempotent
test/generic_server: add test case
configure, cmake: sort the lists of boost unit tests
generic_server: convert connection tracking to seastar::gate
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.