4614fedd22
In replace-with-same-ip a new node calls gossiper.start_gossiping
from join_token_ring with the 'advertise' parameter set to false.
This means that this node will fail echo RPC-s from other nodes,
making it appear as not alive to them. The node changes this only
in storage_service::join_node_response_handler, when the topology
coordinator notifies it that it's actually allowed to join the
cluster. The node calls _gossiper.advertise_to_nodes({}), and
only from this moment other nodes can see it as alive.
The problem is that topology coordinator sends this notification
in topology::transition_state::join_group0 state. In this state
nodes of the cluster already see the new node as pending,
they react with calling tmpr->add_replacing_endpoint and
update_topology_change_info when they process the corresponding
raft notification in sync_raft_topology_nodes. When the new
token_metadata is published, assure_sufficient_live_nodes
sees the new node in pending_endpoints. All of this happen
before the new node handled successful join notification,
so it's not alive yet. Suppose we had a cluster with three
nodes and we're replacing on them with a fourth node.
For cl=qurum assure_sufficient_live_nodes throws if
live < need + pending, which in our case becomes 2 < 2 + 1.
The end effect is that during replace-with-same-ip
data plane requests can fail with unavailable_exception,
breaking availability.
The patch makes boot procedure more similar to node ops one.
It splits the marking of a node as "being replaced" and adding it to
pending set in to different steps and marks it as alive in the middle.
So when the node is in topology::transition_state::join_group0 state
it marked as "being replaced" which means it will no longer be used for
reads and writes. Then, in the next state, new node is marked as alive and
is added to pending list.
fixes scylladb/scylladb#17421
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.