08cbd180ff
Compaction manager can start tons of compaction of fully expired sstable in parallel, which may consume a significant amount of resources. This problem is caused by weight being released too early in compaction, after data is all compacted but before table is called to update its state, like replacing sstables and so on. Fully expired sstables aren't actually compacted, so the following can happen: - compaction 1 starts for expired sst A with weight W, but there's nothing to be compacted, so weight W is released, then calls table to update state. - compaction 2 starts for expired sst B with weight W, but there's nothing to be compacted, so weight W is released, then calls table to update state. - compaction 3 starts for expired sst C with weight W, but there's nothing to be compacted, so weight W is released, then calls table to update state. - compaction 1 is done updating table state, so it finally completes and releases all the resources. - compaction 2 is done updating table state, so it finally completes and releases all the resources. - compaction 3 is done updating table state, so it finally completes and releases all the resources. This happens because, with expired sstable, compaction will release weight faster than it will update table state, as there's nothing to be compacted. With my reproducer, it's very easy to reach 50 parallel compactions on a single shard, but that number can be easily worse depending on the amount of sstables with fully expired data, across all tables. This high parallelism can happen only with a couple of tables, if there are many time windows with expired data, as they can be compacted in parallel. Prior to55a8b6e3c9, weight was released earlier in compaction, before last sstable was sealed, but right now, there's no need to release weight earlier. Weight can be released in a much simpler way, after the compaction is actually done. So such compactions will be serialized from now on. Fixes #8710. Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com> Message-Id: <20210527165443.165198-1-raphaelsc@scylladb.com> [avi: drop now unneeded storage_service_for_tests] (cherry picked from commita7cdd846da)
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.