628e6ffd33
Currently, mutation query on replica side will not respond with a result which doesn't have at least one live row. This causes problems if there is a lot of dead rows or partitions before we reach a live row, which stem from the fact that resulting reconcilable_result will be large: 1. Large allocations. Serialization of reconcilable_result causes large allocations for storing result rows in std::deque 2. Reactor stalls. Serialization of reconcilable_result on the replica side and on the coordinator side causes reactor stalls. This impacts not only the query at hand. For 1M dead rows, freezing takes 130ms, unfreezing takes 500ms. Coordinator does multiple freezes and unfreezes. The reactor stall on the coordinator side is >5s 3. Too large repair mutations. If reconciliation works on large pages, repair may fail due to too large mutation size. 1M dead rows is already too much: Refs https://github.com/scylladb/scylladb/issues/9111. This patch fixes all of the above by making mutation reads respect the memory accounter's limit for the page size, even for dead rows. This patch also addresses the problem of client-side timeouts during paging. Reconciling queries processing long strings of tombstones will now properly page tombstones,like regular queries do. My testing shows that this solution even increases efficiency. I tested with a cluster of 2 nodes, and a table of RF=2. The data layout was as follows (1 partition): * Node1: 1 live row, 1M dead rows * Node2: 1M dead rows, 1 live row This was designed to trigger reconciliation right from the very start of the query. Before: ``` Running query (node2, CL=ONE, cold cache) Query done, duration: 140.0633503ms, pages: 101, result: [Row(pk=0, ck=3000000, v=0)] Running query (node2, CL=ONE, hot cache) Query done, duration: 66.7195275ms, pages: 101, result: [Row(pk=0, ck=3000000, v=0)] Running query (all-nodes, CL=ALL, reconcile, cold-cache) Query done, duration: 873.5400742ms, pages: 2, result: [Row(pk=0, ck=0, v=0), Row(pk=0, ck=3000000, v=0)] ``` After: ``` Running query (node2, CL=ONE, cold cache) Query done, duration: 136.9035122ms, pages: 101, result: [Row(pk=0, ck=3000000, v=0)] Running query (node2, CL=ONE, hot cache) Query done, duration: 69.5286021ms, pages: 101, result: [Row(pk=0, ck=3000000, v=0)] Running query (all-nodes, CL=ALL, reconcile, cold-cache) Query done, duration: 162.6239498ms, pages: 100, result: [Row(pk=0, ck=0, v=0), Row(pk=0, ck=3000000, v=0)] ``` Non-reconciling queries have almost identical duration (1 few ms changes can be observed between runs). Note how in the after case, the reconciling read also produces 100 pages, vs. just 2 pages in the before case, leading to a much lower duration (less than 1/4 of the before). Refs https://github.com/scylladb/scylladb/issues/7929 Refs https://github.com/scylladb/scylladb/issues/3672 Refs https://github.com/scylladb/scylladb/issues/7933 Fixes https://github.com/scylladb/scylladb/issues/9111 Closes #14923 * github.com:scylladb/scylladb: test/topology_custom: add test_read_repair.py replica/mutation_dump: detect end-of-page in range-scans tools/scylla-sstable: write: abort parser thread if writing fails test/pylib: add REST methods to get node exe and workdir paths test/pylib/rest_client: add load_new_sstables, keyspace_{flush,compaction} service/storage_proxy: add trace points for the actual read executor type service/storage_proxy: add trace points for read-repair storage_proxy: Add more trace-level logging to read-repair database: Fix accounting of small partitions in mutation query database, storage_proxy: Reconcile pages with no live rows incrementally
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 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.