4c2e026e04
As the test test_streams_closed_read confirmed, when a stream shard is closed, GetRecords should not return a NextShardIterator at all. Before this patch we wrongly returned an empty string for it. Before this patch, several Alternator Stream tests (in test_streams.py) failed when running against a multi-node Scylla cluster. The reason is as follows: As a multi-node cluster boots and more and more nodes enter the cluster, the cluster changes its mind about the token ownership, and therefore the list of stream shards changes. By the time we have the full cluster, a bunch of shards were created and closed without any data yet. All the tests will see these closed shards, and need to understand them. The fetch_more() utility function correctly assumed that a closed shard does not return a NextShardIterator, and got confused by the empty string we used to return. Now that closed shards can return responses without NextShardIterator, we also needed to fix in this patch a couple of tests which wrongly assumed this can't happen. These tests did not fail on DynamoDB because unlike in Scylla, DynamoDB does not have any closed shards in normal tests which do not specifically cause them (only test_streams_closed_read). We also need to fix test_streams_closed_read to get rid of an unnecessary assumption: It currently assumes that when we read the very last item in a closed shard is read, the end-of-shard is immediately signaled (i.e., NextShardIterator is not returned). Although DynamoDB does in fact do this, it is also perfectly legal for Alternator's implementation to return the last item with a new NextShardIterator - and only when the client reads from that iterator, we finally return the signal the end of the shard. Fixes #7237. Signed-off-by: Nadav Har'El <nyh@scylladb.com> Message-Id: <20200922082529.511199-1-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 in ./docs and on the wiki. There is currently no clear definition of what goes where, so when looking for something be sure to check both. 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.