318278ff92
Currently, each change to tablet metadata triggers a full metadata reload from disk. This is very wasteful, especially if the metadata change affects only a single row in the `system.tablets` table. This is the case when the tablet load balancer triggers a migration, this will affect a single row in the table, but today will trigger a full reload. We expect tablet count to potentially grow to thousands and beyond and the overhead of this full reload can become significant. This PR makes tablet metadata reload partial, instead of reloading all metadata on topology or schema changes, reload only the partitions that are affected by the change. Copy the rest from the in-memory state. This is done with two passes: first the change mutations are scanned and a hint is produced. This hint is then passed down to the reload code, which will use it to only reload parts (rows/partitions) of the metadata that has actually changed. The performance difference between full reload and partial reload is quite drastic: ``` INFO 2024-07-25 05:06:27,347 [shard 0:stat] testlog - Tablet metadata reload: full 616.39ms partial 0.18ms ``` This was measured with the modified (by this PR) `perf_tablets`, which creates 100 tables, each with 2K tablets. The test was modified to change a single tablet, then do a full and partial reload respectively, measuring the time it takes for reach. Fixes: #15294 New feature, no backport needed. Closes scylladb/scylladb#15541 * github.com:scylladb/scylladb: test/perf/perf_tablets: add tablet metadata reload perf measurement test/boost/tablets_test: add test for partial tablet metadata updates db/schema_tables: pass tablet hint to update_tablet_metadata() service/storage_service: load_tablet_metadata(): add hint parameter service/migration_listener: update_tablet_metadata(): add hint parameter service/raft/group0_state_machine: provide tablet change hint on topology change service/storage_service: topology_state_load(): allow providing change hint replica/tablets: add update_tablet_metadata() replica/tablets: fix indentation replica/tablets: extract tablet_metadata builder logic replica/tablets: add get_tablet_metadata_change_hint() and update_tablet_metadata_change_hint() locator/tablets: add tablet_map::clear_tablet_transition_info() locator/tablets: make tablet_metadata cheap to copy mutation/canonical_mutation: add key()
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.