db77b5bd03
This is a followup to #19937, for #19803. See in particular [this comment](https://github.com/scylladb/scylladb/issues/19803#issuecomment-2258371923). The primary conversion target is coroutines. However, while coroutines are the most convenient style, they are only infrequently usable in this case, for the following reasons: - Wherever we have a `future::finally()` that calls a cleanup function that returns a future (which must be awaited), we cannot use `co_await`. We can only use `seastar::async()` with `deferred_close` or `defer()`. - The code passes lots of lambdas, and `co_await` cannot be used in lambdas. First, I tried, and the compiler rejects it; second, a capturing lambda that is a coroutine is a trap [[1]](https://devblogs.microsoft.com/oldnewthing/20211103-00/?p=105870) [[2]](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rcoro-capture). In most cases, I didn't have to use naked `seastar::async()`; there were specialized wrappers in place already. Thus, most of the changes target `seastar::thread` context under existent `seastar::async()` wrappers, and only a few functions end up as coroutines. The last patch in the series (`test/sstable: remove useless variable from promoted_index_read()`) is an independent micro-cleanup, the opportunity for which I thought to have noticed while reading the code. The tail of `test/boost/sstable_test.cc` (the stuff following `promoted_index_read()`) is already written as `seastar::thread`. That's already better (for readability) than future chaining; but could have I perhaps further converted those functions to coroutines? My answer was "no": - Some of the candidate functions relied on deferred cleanups that might need to yield (all three variants of `count_rows()`). - Some had been implemented by passing lambdas to wrappers of `seastar::async()` (`sub_partition_read()`, `sub_partitions_read()`). - The test case `test_skipping_in_compressed_stream()` initially looked promising for co-routinization (from its starting point `seastar::async()`), because it seemed to employ no deferred cleanup (that might need to yield). However, the function uses three lambdas that must be able to yield internally, and one of those (`make_is()`) is even capturing. - The rest (`test_empty_key_view_comparison()`, `test_parse_path_good()`, `test_parse_path_bad()`) was synchronous code to begin with. ``` test/boost/sstable_test.cc | 188 +++++++++----------- 1 file changed, 83 insertions(+), 105 deletions(-) ``` Refactoring; no backport needed. Closes scylladb/scylladb#20011 * github.com:scylladb/scylladb: test/sstable: remove useless variable from promoted_index_read() test/sstable: rewrite promoted_index_read() with async() test/sstable: unfuturize lambda invocation in test_using_reusable_sst*() test/sstable: rewrite wrong_range() with async() test/sstable: simplify not_find_key_composite_bucket0() under test_using_reusable_sst() test/sstable: rewrite full_index_search() with async() test/sstable: simplify find_key*(), all_in_place() under test_using_reusable_sst() test/sstable: rewrite (un)compressed_random_access_read() with async() test/sstable: simplify write_and_validate_sst() test/sstable: simplify check_toc_func() under async() test/sstable: simplify check_statistics_func() under async() test/sstable: simplify check_summary_func() under async() test/sstable: coroutinize check_component_integrity() test/sstable: rewrite write_sst_info() with async() test/sstable: simplify missing_summary_first_last_sane() test/sstable: coroutinize summary_query_fail() test/sstable: rewrite summary_query() with async() test/sstable: coroutinize (simple/composite)_index_read() test/sstable: rewrite index_read() with async() test/sstable: rewrite test_using_reusable_sst() with async() test/sstable: rewrite test_using_working_sst() with async()
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 API - CQL. 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.