cb0b8d1903
This will prevent accumulation of unnecessary dummy entries. A single-partition populating scan with clustering key restrictions will insert dummy entries positioned at the boundaries of the clustering query range to mark the newly populated range as continuous. Those dummy entries may accumulate with time, increasing the cost of the scan, which needs to walk over them. In some workloads we could prevent this. If a populating query overlaps with dummy entries, we could erase the old dummy entry since it will not be needed, it will fall inside a broader continuous range. This will be the case for time series worklodas which scan with a decreasing (newest) lower bound. Refs #8153. _last_row is now updated atomically with _next_row. Before, _last_row was moved first. If exception was thrown and the section was retried, this could cause the wrong entry to be removed (new next instead of old last) by the new algorithm. I don't think this was causing problems before this patch. The problem is not solved for all the cases. After this patch, we remove dummies only when there is a single MVCC version. We could patch apply_monotonically() to also do it, so that dummies which are inside continuous ranges are eventually removed, but this is left for later. perf_row_cache_reads output after that patch shows that the second scan touches no dummies: $ build/release/test/perf/perf_row_cache_reads_g -c1 -m200M Rows in cache: 0 Populating with dummy rows Rows in cache: 265320 Scanning read: 142.621613 [ms], preemption: {count: 639, 99%: 0.545791 [ms], max: 0.526929 [ms]}, cache: 0/0 [MB] read: 0.023197 [ms], preemption: {count: 1, 99%: 0.035425 [ms], max: 0.032736 [ms]}, cache: 0/0 [MB] Message-Id: <20210226172801.800264-1-tgrabiec@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.