6e5aaa85b6
Work in this patch is a result of two bugs - spurious MODIFY event, when remove column is used in `update_item` on non-existing item and spurious events, when batch write item mixed noop operations with operations involving actual changes (the former would still emit cdc log entries). The latter issue required rework of Piotr Wieczorek's algorithm, which fixed former issue as well. Piotr Wieczorek previously wrote checks, that should prevent unnecesary cdc events from being written. His implementation missed the fact, that a single `mutation` object passed to cdc code to be analysed for cdc log entries can contain modifications for multiple rows (with the same timestamp - for example as a result to BatchWriteItem call). His code tries to skip whole `mutation`, which in such case is not possible, because BatchWriteItem might have one item that does nothing and second item that does modification (this is the reason for the second bug). His algorithm was extended and moved. Originally it was working as follows - user would sent a `mutation` object with some changes to be "augmented". The cdc would process those changes and built a set of cdc log changes based on them, that would be added to cdc log table. Piotr added a `should_skip` function, which processes user changes and tried to determine if they all should be dropped or not. New version, instead of trying to skip adding rows to cdc log `mutation` object, builds a rows-to-ignore set. After whole cdc log `mutation` object is completed, it processes it and go through it row by row. Any row that was previously added to a `rows_to_ignore` set will now be removed. Remaining rows are written to new cdc log `mutation` with new clustering key (`cdc$batch_seq_no` index value should probably be consecutive - we just want to be safe here) and returns new `mutation` object to be sent to cdc log table. The first bug is fixed as a side effect of new algorithm, which contains more precise checks detecting, if given mutation actually made a difference. Fixes: #28368 Fixes: SCYLLADB-538 Fixes: SCYLLADB-1528 Refs: #28452
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.