87cd7e8741
This commit is a first part of the fix for #14675. The issue is about the test test_joining_old_node_fails faling occasionally with experimental_features: [consistent-topology-changes]. The next commit contains a fix for it, here we solve the pre-existing gossiper problem which we stumble upon after the fix. Local generation for addr may have been increased since the current node sent an initial SYN. Comparing versions across different generations in get_state_for_version_bigger_than could result in loosing some app states with smaller versions. More specifically, consider a cluster with nodes .1, .2, .3, .3 has .1 and .2 as seeds, .2 has .1 as a seed. Suppose .2 receives a SYN from .3 before its gossiper starts, and it has a version 0.24 for .1 in endpoint_states. The digest from .3 contains 0.25 as a version for .1, so examine_gossiper produces .1->0.24 as a digest and this digest is send to .3 as part of the ack. Before processing this ack, .3 processed an ack from .1 (scylla sends SYN to many nodes) and updates its endpoint_states according to it, so now it has .1->100500.32 for .1. Then we get to do_send_ack2_msg and call get_state_for_version_bigger_than(.1, 24). This returns properties which has version > 24, ignoring a lot of them with smaller versions which has been received from .1. Also, get_state_for_version_bigger_than updates generation (it copies get_heart_beat_state from .3), so when we apply the ack in handle_ack2_msg at .2 we update the generation and now the skipped app states will only be updated on .2 if somebody change them and increment their version. Cassandra behaviour is the same in this case (see https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/gms/GossipDigestAckVerbHandler.java#L86). This is probably less of a problem for them since most of the time they send only one SYN in one gossiper round (save for unreachable nodes), so there is less room for conflicts.
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.
- 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 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 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.