c5dc086baf
The ANN vector queries with all-zero vectors are allowed even on vector indexes with similarity function set to cosine. When enabling the rescoring option, those queries would fail as the rescoring calls `similarity_cosine` function underneath, causing an `InvalidRequest` exception as all-zero vectors were not allowed matching Cassandra's behaviour. To eliminate the discrepancy we want the all-zero vector `similarity_cosine` calls to pass, but return the NaN as the cosine similarity for zero vectors is mathematically incorrect. We decided not to use arbitrary values contrary to USearch, for which the distance (not to be confused with similarity) is defined as cos(0, 0) = 0, cos(0, x) = 1 while supporting the range of values [0, 2]. If we wanted to convert that to similarity, that would mean sim_cos(0, x) = 0.5, which does not support mathematical reasoning why that would be more similar than for example vectors marking obtuse angles. It's safe to assume that all-zero vectors for cosine similarity shouldn't make any impact, therefore we return NaN and eliminate them from best results. Adjusted the tests accordingly to check both proper Cassandra and Scylla's behaviour. Fixes: SCYLLADB-456 Backport to 2026.1 needed, as it fixes the bug for ANN vector queries using rescoring introduced there. Closes scylladb/scylladb#28609 * github.com:scylladb/scylladb: test/vector_search: add reproducer for rescoring with zero vectors vector_search: return NaN for similarity_cosine with all-zero vectors
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.