f0950e023d
Until now, the lists of streams in the `cdc_streams_descriptions` table for a given generation were stored in a single collection. This solution has multiple problems when dealing with large clusters (which produce large lists of streams): 1. large allocations 2. reactor stalls 3. mutations too large to even fit in commitlog segments This commit changes the schema of the table as described in issue #7993. The streams are grouped according to token ranges, each token range being represented by a separate clustering row. Rows are inserted in reasonably large batches for efficiency. The table is renamed to enable easy upgrade. On upgrade, the latest CDC generation's list of streams will be (re-)inserted into the new table. Yet another table is added: one that contains only the generation timestamps clustered in a single partition. This makes it easy for CDC clients to learn about new generations. It also enables an elegant two-phase insertion procedure of the generation description: first we insert the streams; only after ensuring that a quorum of replicas contains them, we insert the timestamp. Thus, if any client observes a timestamp in the timestamps table (even using a ONE query), it means that a quorum of replicas must contain the list of streams. --- Nodes automatically ensure that the latest CDC generation's list of streams is present in the streams description table. When a new generation appears, we only need to update the table for this generation; old generations are already inserted. However, we've changed the description table (from `cdc_streams_descriptions` to `cdc_streams_descriptions_v2`). The existing mechanism only ensures that the latest generation appears in the new description table. We add an additional procedure that rewrites the older generations as well, if we find that it is necessary to do so (i.e. when some CDC log tables may contain data in these generations). Closes #8116 * github.com:scylladb/scylla: tests: add a simple CDC cql pytest cdc: add config option to disable streams rewriting cdc: rewrite streams to the new description table cql3: query_processor: improve internal paged query API cdc: introduce no_generation_data_exception exception type docs: cdc: mention system.cdc_local table cdc: coroutinize do_update_streams_description sys_dist_ks: split CDC streams table partitions into clustered rows cdc: use chunked_vector for streams in streams_version cdc: remove `streams_version::expired` field system_distributed_keyspace: use mutation API to insert CDC streams storage_service: don't use `sys_dist_ks` before it is started
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++20 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 APIs - CQL and Thrift. 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 users mailing list and Slack channel are for users to discuss configuration, management, and operations of the ScyllaDB open source.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.