fc4c2df2ce
We currently do it only for a bootstrapping node, which is a bug. The missing IP can cause an internal error, for example, in the following scenario: - replace fails during streaming, - all live nodes are shut down before the rollback of replace completes, - all live nodes are restarted, - live nodes start hitting internal error in all operations that require IP of the replacing node (like client requests or REST API requests coming from nodetool). We fix the bug here, but we do it separately for replace with different IP and replace with the same IP. For replace with different IP, we persist the IP -> host ID mapping in `system.peers` just like for bootstrap. That's necessary, since there is no other way to determine IP of the replacing node on restart. For replace with the same IP, we can't do the same. This would require deleting the row corresponding to the node being replaced from `system.peers`. That's fine in theory, as that node is permanently banned, so its IP shouldn't be needed. Unfortunately, we have many places in the code where we assume that IP of a topology member is always present in the address map or that a topology member is always present in the gossiper endpoint set. Examples of such places: - nodetool operations, - REST API endpoints, - `db::hints::manager::store_hint`, - `group0_voter_handler::update_nodes`. We could fix all those places and verify that drivers work properly when they see a node in the token metadata, but not in `system.peers`. However, that would be too risky to backport. We take a different approach. We recover IP of the replacing node on restart based on the state of the topology state machine and `system.peers` just after loading `system.peers`. We rely on the fact that group 0 is set up at this point. The only case where this assumption is incorrect is a restart in the Raft-based recovery procedure. However, hitting this problem then seems improbable, and even if it happens, we can restart the node again after ensuring that no client and REST API requests come before replace is rolled back on the new topology coordinator. Hence, it's not worth to complicate the fix (by e.g. looking at the persistent topology state instead of the in-memory state machine).
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 ScyllaDB.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.