8385f3eb21
In the sstable reader, we iterate over clustering ranges using the index_reader, which normally only accepts advancing to increasing positions. In this patch we add methods for advancing the index reader in reverse. To simplify our job we restrict our attention to a single implementation of the promoted index block cursor: `bsearch_clustered_cursor`. The `index_reader` methods for advancing in reverse will thus assume that this implementation is used. The assumption is correct given that we're working only with sstables of versions >= mc, which is indeed the intended use case. We add some documentation in appropriate places to make this obvious. We extend `bsearch_clustered_cursor` with two methods: `advance_past(pos)`, which advances the cursor to the first block after `pos` (or to the end if there is no such block), and `last_block_offset()`, which returns the data file offset of the first row from the last promoted index block. To efficiently find the position in the data file of the last row of the partition (which we need when performing a reversed query) the sstable reader may need to read the span of the entire last promoted index block in the data file. To learn where the block starts it can use `index_reader::last_block_offset()`, which is implemented in terms of `bsearch_clustered_cursor::last_block_offset()`. When performing a single partition read in forward order, the reader asks the index to position its lower bound at the start of the partition and its upper bound after the end of the slice. It starts by reading the first range. After exhausting a range it jumps to the next one by asking the index to advance the lower bound. For reverse single partition reads we'll take a similar approach: the initial bound positions are as in the forward case. However, we start with the last range and after exhausting a range we want to jump to a previous one; we will do it by advancing the upper bound in reverse (i.e. moving it closer to the beginning of the partition). For this we introduce the `index_reader::advance_reverse` function.
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.