b3e39d81aa
We introduce a new single-key sstable reader for sstables created by `TimeWindowCompactionStrategy`. The reader uses the fact that sstables created by TWCS are mostly disjoint with respect to the contained `position_in_partition`s in order to avoid having multiple sstable readers opened at the same time unnecessarily. In case there are overlapping ranges (for example, in the current time-window), it performs the necessary merging (it uses `clustering_order_reader_merger`, introduced recently). The reader uses min/max clustering key metadata present in `md` sstables in order to decide when to open or close a sstable reader. The following experiment was performed: 1. create a TWCS table with 1 minute windows 2. fill the table with 8 equal windows of data (each window flushed to a separate sstable) 3. perform `select * from ks.t where pk = 0 limit 1` query with and without the change The expectation is that with the commit, only one sstable will be opened to fetch that one row; without the commit all 8 sstables would be opened at once. The difference in the value of `scylla_reactor_aio_bytes_read` was measured (value after the query minus value before the query), both with and without the commit. With the commit, the difference was 67584. Without the commit, the difference was 528384. 528384 / 67584 ~= 7.8. Fixes #6418. Closes #7437 * github.com:scylladb/scylla: sstables: gather clustering key filtering statistics in TWCS single key reader sstables: use time_series_sstable_set in time_window_compaction_strategy sstable_set: new reader for TWCS single partition queries mutation_reader_test: test clustering_order_reader_merger with time_series_sstable_set sstable_set: introduce min_position_reader_queue sstable_set: introduce time_series_sstable_set sstables: add min_position and max_position accessors sstable_set: make create_single_key_sstable_reader a virtual method clustering_order_reader_merger: fix the 0 readers case
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.