13c043903d
When a non-replica node handles a strongly consistent write, it must forward the request to a replica. If the closest replica is not the leader, the request gets redirected again, causing an extra roundtrip. Add a leader location cache in groups_manager, keyed by raft group_id. After a write request is forwarded, the CQL transport layer records the final node as the leader in the cache. Subsequent write requests from the same node for the same group are forwarded directly to the cached leader, eliminating the extra roundtrip. The cache is only used for writes. Reads can be served by any replica, so they skip the cache and use proximity-based routing instead. Cache entries are validated at use time: if the cached leader is no longer a replica (e.g. after tablet migration), the entry is evicted and the normal closest-replica path is taken. This prevents a scenario where two nodes keep redirecting to each other because both think that the other is the leader but actually both are non-replicas - such loop is broken as soon as the tablet maps are updated. On token_metadata updates, entries for groups that no longer exist (e.g. table dropped, tablet merged) are evicted. Entries for groups that still exist are kept — use-time validation handles staleness. An on_node_resolved callback is propagated through the redirect/bounce path so the transport layer can update the cache generically without coupling to the strong-consistency coordinator. The coordinator creates the callback only for writes (capturing the groups_manager and group_id) and attaches it to the bounce message; the transport layer invokes it once the final node is known, keeping the forwarding infrastructure subsystem-agnostic. We also add a test which verifies that after the initial redirect, following requests to the same node avoid the extra redirect and forward directly to the leader. Fixes: SCYLLADB-1064 Closes scylladb/scylladb#29392
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.