e4b2dfb54d
The current implementation of the Alternator expiration (TTL) feature has each node scan for expired partitions in its own primary ranges. This means that while a node is down, items in its primary ranges will not get expired. But we note that doesn't have to be this way: If only a single node is down, and RF=3, the items that node owns are still readable with QUORUM - so these items can still be safely read and checked for expiration - and also deleted. This patch implements a fairly simple solution: When a node completes scanning its own primary ranges, also checks whether any of its *secondary* ranges (ranges where it is the *second* replica) has its primary owner down. For such ranges, this node will scan them as well. This secondary scan stops if the remote node comes back up, but in that case it may happen that both nodes will work on the same range at the same time. The risks in that are minimal, though, and amount to wasted work and duplicate deletion records in CDC. In the future we could avoid this by using LWT to claim ownership on a range being scanned. We have a new dtest (see a separate patch), alternator_ttl_tests.py:: TestAlternatorTTL::test_expiration_with_down_node, which reproduces this and verifies this fix. The test starts a 5-node cluster, with 1000 items with random tokens which are due to be expired immediately. The test expects to see all items expiring ASAP, but when one of the five nodes is brought down, this doesn't happen: Some of the items are not expired, until this patch is used. Fixes #9787 Signed-off-by: Nadav Har'El <nyh@scylladb.com> Message-Id: <20211222131933.406148-1-nyh@scylladb.com>
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.