bdeef77f20
Whenever a Raft configuration change is performed, `raft::server` calls `raft_rpc::add_server`/`raft_rpc::remove_server`. Our `raft_rpc` implementation has a function, `_on_server_update`, passed in the constructor, which it called in `add_server`/`remove_server`; that function would update the set of endpoints detected by the direct failure detector. `_on_server_update` was passed an IP address and that address was added to / removed from the failure detector set (there's another translation layer between the IP addresses and internal failure detector 'endpoint ID's; but we can ignore it for the purposes of this commit). Therefore: the failure detector was pinging a certain set of IP addresses. These IP addresses were updated during Raft configuration changes. To implement the `is_alive(raft::server_id)` function (required by `raft::failure_detector` interface), we would translate the ID using the Raft address map, which is currently also updated during configuration changes, to an IP address, and check if that IP address is alive according to the direct failure detector (which maintained an `_alive_set` of type `unordered_set<gms::inet_address>`). This all works well but it assumes that servers can be identified using IP addresses - it doesn't play well with the fact that servers may change their IP addresses. The only immutable identifier we have for a server is `raft::server_id`. In the future, Raft configurations will not associate IP addresses with Raft servers; instead we will assume that IP addresses can change at any time, and there will be a different mechanism that eventually updates the Raft address map with the latest IP address for each `raft::server_id`. To prepare us for that future, in this commit we no longer operate in terms of IP addresses in the failure detector, but in terms of `raft::server_id`s. Most of the commit is boilerplate, changing `gms::inet_address` to `raft::server_id` and function/variable names. The interesting changes are: - in `is_alive`, we no longer need to translate the `raft::server_id` to an IP address, because now the stored `_alive_set` already contains `raft::server_id`s instead of `gms::inet_address`es. - the `ping` function now takes a `raft::server_id` instead of `gms::inet_address`. To send the ping message, we need to translate this to IP address; we do it by the `raft_address_map` pointer introduced in an earlier commit. Thus, there is still a point where we have to translate between `raft::server_id` and `gms::inet_address`; but observe we now do it at the last possible moment - just before sending the message. If we have no translation, we consider the `ping` to have failed - it's equivalent to a network failure where no route to a given address was found.
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 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.