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This series switches memtable and cache to use a new representation for mutation data, called `mutation_partition_v2`. In this representation, range tombstone information is stored in the same tree as rows, attached to row entries. Each entry has a new tombstone field, which represents range tombstone part which applies to the interval between this entry and the previous one. See docs/dev/mvcc.md for more details about the format. The transient mutation object still uses the old model in order to avoid work needed to adapt old code to the new model. It may also be a good idea to live with two models, since the transient mutation has different requirements and thus different trade-offs can be made. Transient mutation doesn't need to support eviction and strong exception guarantees, so its algorithms and in-memory representation can be simpler. This allows us to incrementally evict range tombstone information. Before this series, range tombstones were accumulated and evicted only when the whole partition entry was evicted. This could lead to inefficient use of cache memory. Another advantage of the new representation is that reads don't have to lookup range tombstone information in a different tree while reading. This leads to simpler and more efficient readers. There are several disadvantages too. Firstly, rows_entry is now larger by 16 bytes. Secondly, update algorithms are more complex because they need to deoverlap range tombstone information. Also, to handle preemption and provide strong exception guarantees, update algorithms may need to allocate sentinel entries, which adds complexity and reduces performance. The memtable reader was changed to use the same cursor implementation which cache uses, for improved code reuse and reducing risk of bugs due to discrepancy of algorithms which deal with MVCC. Remaining work: - performance optimizations to apply_monotonically() to avoid regressions - performance testing - preemption support in apply_to_incomplete (cache update from memtable) Fixes #2578 Fixes #3288 Fixes #10587 Closes #12048 * github.com:scylladb/scylladb: test: mvcc: Extend some scenarios with exhaustive consistency checks on eviction test: mvcc: Extract mvcc_container::allocate_in_region() row_cache, lru: Introduce evict_shallow() test: mvcc: Avoid copies of mutation under failure injection test: mvcc: Add missing logalloc::reclaim_lock to test_apply_is_atomic mutation_partition_v2: Avoid full scan when applying mutation to non-evictable Pass is_evictable to apply() tests: mutation_partition_v2: Introduce test_external_memory_usage_v2 mirroring the test for v1 tests: mutation: Fix test_external_memory_usage() to not measure mutation object footprint tests: mutation_partition_v2: Add test for exception safety of mutation merging tests: Add tests for the mutation_partition_v2 model mutation_partition_v2: Implement compact() cache_tracker: Extract insert(mutation_partition_v2&) mvcc, mutation_partition: Document guarantees in case merging succeeds mutation_partition_v2: Accept arbitrary preemption source in apply_monotonically() mutation_partition_v2: Simplify get_continuity() row_cache: Distinguish dummy insertion site in trace log db: Use mutation_partition_v2 in mvcc range_tombstone_change_merger: Introduce peek() readers: Extract range_tombstone_change_merger mvcc: partition_snapshot_row_cursor: Handle non-evictable snapshots mvcc: partition_snapshot_row_cursor: Support digest calculation mutation_partition_v2: Store range tombstones together with rows db: Introduce mutation_partition_v2 doc: Introduce docs/dev/mvcc.md db: cache_tracker: Introduce insert() variant which positions before existing entry in the LRU db: Print range_tombstone bounds as position_in_partition test: memtable_test: Relax test_segment_migration_during_flush test: cache_flat_mutation_reader: Avoid timestamp clash test: cache_flat_mutation_reader_test: Use monotonic timestamps when inserting rows test: mvcc: Fix sporadic failures due to compact_for_compaction() test: lib: random_mutation_generator: Produce partition tombstone less often test: lib: random_utils: Introduce with_probability() test: lib: Improve error message in has_same_continuity() test: mvcc: mvcc_container: Avoid UB in tracker() getter when there is no tracker test: mvcc: Insert entries in the tracker test: mvcc_test: Do not set dummy::no on non-clustering rows mutation_partition: Print full position in error report in append_clustered_row() db: mutation_cleaner: Extract make_region_space_guard() position_in_partition: Optimize equality check mvcc: Fix version merging state resetting mutation_partition: apply_resume: Mark operator bool() as explicit
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.