ca9422ca73
The lockup: When view_builder starts all shards at some point get to a barrier waiting for each other to pass. If any shard misses this checkpoint, all others stuck forever. As this barrier lives inside the _started future, which in turn is waited on stop, the stop stucks as well. Reasons to miss the barrier -- exception in the middle of the fun^w start or explicit abort request while waiting for the schema agreement. Fix the "exception" case by unlocking the barrier promise with exception and fix the "abort request" case by turning it into an exception. The bug can be reproduced by hands if making one shard never see the schema agreement and continue looping until the abort request. The crash: If the background start up fails, then the _started future is resolved into exception. The view_builder::stop then turns this future into a real exception caught-and-rethrown by main.cc. This seems wrong that a failure in a background fiber aborts the regular shutdown that may proceed otherwise. tests: unit(dev), manual start-stop branch: https://github.com/xemul/scylla/tree/br-view-builder-shutdown-fix-3 fixes: #7077 Patch #5 leaves the seastar::async() in the 1-st phase of the start() although can also be tuned not to produce a thread. However, there's one more (painless) issue with the _sem usage, so this change appears too large for the part of the bug-fix and will come as a followup. * 'br-view-builder-shutdown-fix-3' of git://github.com/xemul/scylla: view_builder: Add comment about builder instances life-times view_builder: Do sleep abortable view_builder: Wakeup barrier on exception view_builder: Always resolve started future to success view_builder: Re-futurize start view_builder: Split calculate_shard_build_step into two view_builder: Populate the view_builder_init_state view_builder: Fix indentation after previous patch view_builder: Introduce view_builder_init_state
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.
- Packaging documentation on how to build Scylla packages for different Linux distributions.
- 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 in ./docs and on the wiki. There is currently no clear definition of what goes where, so when looking for something be sure to check both. 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 users mailing list 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.