33dbb63aef
In an earlier patch, we used the CQL grammar's "subscriptExpr" in the rule for WRITETIME() and TTL(). But since we also wanted these to support UDT fields (x.a), not just collection subscripts (x[3]), we expanded subscriptExpr to also support the field syntax. But LWT expressions already used this subscriptExpr, which meant that LWT expressions unintentionally gained support for UDT fields. Missing support for UDT fields in LWT is a long-standing known Cassandra-compatibility bug (#13624), and now our grammar finally supports the missing syntax. But supporting the syntax is not enough for correct implementation of this feature - we also need to fix the expression handling: Two bugs prevented expressions like `v.a = 0` from working in LWT IF clauses, where `v` is a column of user-defined type. The first bug was in get_lhs_receiver() in prepare_expr.cc: it lacked a handler for field_selection nodes, causing an "unexpected expression" internal error when preparing a condition like `IF v.a = 0`. The fix adds a handler that returns a column_specification whose type is taken from the prepared field_selection's type field. The second bug was in search_and_replace() in expression.cc: when recursing into a field_selection node it reconstructed it with only `structure` and `field`, silently dropping the `field_idx` and `type` fields that are set during preparation. As a result, any transformation that uses search_and_replace() on a prepared expression containing a field_selection — such as adjust_for_collection_as_maps() called from column_condition_prepare() — would zero out those fields. At evaluation time, type_of() on the field_selection returned a null data_type pointer, causing a segmentation fault when the comparison operator tried to call ->equal() through it. The fix preserves field_idx and type when reconstructing the node. Fixes #13624.
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.