0d35c96ef4
Fixes #16298 The adjusted buffer position calculation in buffer_position(), introduced in #15494 was in fact broken. It calculated (like previously) a "position" based on diff between underlying buffer size and ostream size() (i.e. avail), then adjusted this according to sector overhead rules. However, the underlying buffer size is in unadjusted terms, and the ostream is adjusted. The two cannot be compared as such, which means the "positions" we get here are borked. Luckily for us (sarcasm), the position calculation in replayer made a similar error, in that it adjusts up current position by one sector overhead to much, leading to us more or less getting the same, erroneous results in both ends. However, when/iff one needs to adjust the segment file format further, one might very quickly realize that this does not work well if, say, one needs to be able to safely read some extra bytes before first chunk in a segment. Conversely, trying to adjust this also exposes a latent potential error in the skip mechanism, manifesting here. Issue fixed by keeping track of the initial ostream capacity for segment buffer, and use this for position calculation, and in the case of replayer, move file pos adjustment from read_data() to subroutine (shared with skipping), that better takes data stream position vs. file position adjustment. In implementaion terms, we first inc the "data stream" pos (i.e. pos in data without overhead), then adjust for overhead. Also fix replayer::skip, so that we handle the buffer/pos relation correctly now. Added test for intial entry position, as well as data replay consistency for single entry_writer paths.
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 community forum 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.