ae0d77257f
When a mutation generates more view updates than max_rows_for_view_updates (100), view_update_builder::build_some() splits the work into multiple batches. There was a bug in how fragments were read between batches: When should_stop_updates() returned true, the old code called stop() which returned stop_iteration::yes without reading the next fragments. On the next build_some() call, read_both_next_fragments() was called at the start, which advanced BOTH readers - skipping any fragment that was already read but not yet consumed. A row could be not consumed if either: - the 100th (last in the batch) update was a row insertion and we still had insertions/updates remaining - the 100th (last in the batch) update was a row deletion and we still had deletions/updates remaining For the most common case where work is split in batches, i.e. range deletions, we couldn't hit this because range delete generates only view row deletions. On tables with a single materialized view, we also couldn't get this for any batches with less than 50 statements (unless the batch also contained range deletions), because one non-range-delete update can generate up to 2 view updates. Howeveer, for a range of scenarios outside these 2, we could lose view updates, resulting in persistent inconsistencies. The fix: - read_*_next_fragment() now accept a stop_iteration parameter, so the next fragments are always read after consuming (even when stopping), but stop_iteration::yes is correctly propagated to break the loop. - build_some() no longer re-reads fragments at the start. Instead, an initialize() method performs the initial read once at construction. - because now we only advance readers after consuming, we won't advance readers after end_of_partition, so we extend the break condition to accept either readers evaluating to `false` or them being at the end_of_partition. We also handle the optimization with _skip_row_updates Fixes: scylladb/scylladb#29155 Closes scylladb/scylladb#29498
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.