69684e16d8
This PR extends Scylla's SSTable compression with the ability to use compression dictionaries shared across compression chunks. This involves several changes: - We refactor `compression_parameters` and friends (`compressor`, `sstables::local_compression`, `sstables::compression`) to prepare for making the construction of `compressor`s asynchronous, to enable sharing pieces of compressors (the dictionaries) across shards. - We introduce the notion of "hidden compression options" which are written to `CompressionInfo.db` and used to construct decompressors, like regular options, but don't appear in the schema. (We later stuff the SSTable's dictionary into `CompressionInfo.db` using a sequence of such options). - We add a cluster feature which guards the creation of dictionary-compressed SSTables. - We introduce a central "compressor factory" (one instance shared by all shards), which from this point onward is used to construct all `compressor` objects (one per SSTable) used to process the SSTables. When constructing a compressor for writing, it uses the "current"/"recommended" dictionary (which is passed to the factory from the actively-observed contents of the group0-managed `system.dicts`). When constructing a compressor for reading, it uses the dictionary written in the hidden compression options in CompressionInfo.db. And it keeps dictionaries deduplicated, so that each unique live dictionary blob has only one instance in memory, shared across shards. - We teach the relevant `lz4` and `zstd` compressor wrappers about the dictionaries. - We add a HTTP API call which samples pieces of the given table (i.e. the Data.db files) from across the cluster, trains a dictionary on it, and publishes it via `system.dicts` as the new current dictionary for that table. (And we add some RPC verbs to support that). - We add a HTTP API call which estimates the impact of various available compression configurations on the compression ratio. - We add an autotrainer fiber which periodically retrains dicts for dict-aware tables and publishes them if they seem to be a significant improvement. Known imperfections: - The factory currently keeps one dictionary instance on the entire node, but we probably want one copy per NUMA node. I didn't do that because exposing NUMA knowledge to Scylla seems to require some changes in Seastar first. New feature, no backporting involved. Closes scylladb/scylladb#23025 * github.com:scylladb/scylladb: docs: add user-facing documentation for SSTable compression with shared dicts docs/dev: add sstable-compression-dicts.md test: add test_sstable_compression_dictionaries_autotrain.py test: add test_sstable_compression_dictionaries_basic.py test/pylib/rest_client: add `keyspace_upgrade_sstables` helper main: run a sstable_dict_autotrainer api: add the estimate_compression_ratios API call dict_autotrainer: introduce sstable_dict_autotrainer db/system_keyspace: add query_dict_timestamp compress: add ZstdWithDictsCompressor and LZ4WithDictsCompressor main: clean up sstable compression dicts after table drops sstables/compress: discard hidden compression options after the decompressor is created compress: change compressor_ptr from shared_ptr to unique_ptr api: add the retrain_dict API call storage_service: add some dict-related routines main: in compression_dict_updated_callback, recognize and use SSTable compression dicts storage_service: add do_sample_sstables() messaging_service: add SAMPLE_SSTABLES and ESTIMATE_SSTABLE_VOLUME verbs db/system_keyspace: let `system.dicts` helpers be used for dicts other than the RPC compression dict raft/group0_state_machine: on `system.dicts` mutations, pass the affected partitition keys to the callback database: add sample_data_files() database: add take_sstable_set_snapshot() compress: teach `lz4_processor` about dictionaries compress: teach `zstd_processor` about dictionaries sstables: delegate compressor creation to the compressor factory sstables: plug an `sstable_compressor_factory` into `sstables_manager` sstables: introduce sstable_compressor_factory utils/hashers: add get_sha256() gms/feature_service: add the SSTABLE_COMPRESSION_DICTS cluster feature compress: add hidden dictionary options compress: remove `compression_parameters::get_compressor()` sstables/compress: remove get_sstable_compressor() sstables/compress: move ownership of `compressor` to `sstable::compression` compress: remove compressor::option_names() compress: clean up the constructor of zstd_processor compress: squash zstd.cc into compress.cc sstables/compress: break the dependency of `compression_parameters` on `compressor` compress.hh: switch compressor::name() from an instance member to a virtual call bytes: adapt fmt_hex to std::span<const std::byte>
Scylla unit tests using C++ and the Boost test framework
The source files in this directory are Scylla unit tests written in C++ using the Boost.Test framework. These unit tests come in three flavors:
-
Some simple tests that check stand-alone C++ functions or classes use Boost's
BOOST_AUTO_TEST_CASE. -
Some tests require Seastar features, and need to be declared with Seastar's extensions to Boost.Test, namely
SEASTAR_TEST_CASE. -
Even more elaborate tests require not just a functioning Seastar environment but also a complete (or partial) Scylla environment. Those tests use the
do_with_cql_env()ordo_with_cql_env_thread()function to set up a mostly-functioning environment behaving like a single-node Scylla, in which the test can run.
While we have many tests of the third flavor, writing new tests of this type should be reserved to white box tests - tests where it is necessary to inspect or control Scylla internals that do not have user-facing APIs such as CQL. In contrast, black-box tests - tests that can be written only using user-facing APIs, should be written in one of newer test frameworks that we offer - such as test/cqlpy or test/alternator (in Python, using the CQL or DynamoDB APIs respectively) or test/cql (using textual CQL commands), or - if more than one Scylla node is needed for a test - using the test/topology* framework.
Running tests
Because these are C++ tests, they need to be compiled before running.
To compile a single test executable row_cache_test, use a command like
ninja build/dev/test/boost/row_cache_test
You can also use ninja dev-test to build all C++ tests, or use
ninja deb-build to build the C++ tests and also the full Scylla executable
(however, note that full Scylla executable isn't needed to run Boost tests).
Replace "dev" by "debug" or "release" in the examples above and below to use the "debug" build mode (which, importantly, compiles the test with ASAN and UBSAN enabling on and helps catch difficult-to-catch use-after-free bugs) or the "release" build mode (optimized for run speed).
To run an entire test file row_cache_test, including all its test
functions, use a command like:
build/dev/test/boost/row_cache_test -- -c1 -m1G
to run a single test function test_reproduce_18045() from the longer test
file, use a command like:
build/dev/test/boost/row_cache_test -t test_reproduce_18045 -- -c1 -m1G
In these command lines, the parameters before the -- are passed to
Boost.Test, while the parameters after the -- are passed to the test code,
and in particular to Seastar. In this example Seastar is asked to run on one
CPU (-c1) and use 1G of memory (-m1G) instead of hogging the entire
machine. The Boost.Test option -t test_reproduce_18045 asks it to run just
this one test function instead of all the test functions in the executable.
Unfortunately, interrupting a running test with control-C while doesn't
work. This is a known bug (#5696). Kill a test with SIGKILL (-9) if you
need to kill it while it's running.
Boost tests can also be run using test.py - which is a script that provides a uniform way to run all tests in scylladb.git - C++ tests, Python tests, etc.
Execution with pytest
To run all tests with pytest execute
pytest test/boost
To execute all tests in one file, provide the path to the source filename as a parameter
pytest test/boost/aggregate_fcts_test.cc
Since it's a normal path, autocompletion works in the terminal out of the box.
To execute only one test function, provide the path to the source file and function name
pytest --mode dev test/boost/aggregate_fcts_test.cc::test_aggregate_avg
To provide a specific mode, use the next parameter --mode dev,
if parameter isn't provided pytest tries to use ninja mode_list to find out the compiled modes.
Parallel execution is controlled by pytest-xdist and the parameter -n auto.
This command starts tests with the number of workers equal to CPU cores.
The useful command to discover the tests in the file or directory is
pytest --collect-only -q --mode dev test/boost/aggregate_fcts_test.cc
That will return all test functions in the file.
To execute only one function from the test, you can invoke the output from the previous command.
However, suffix for mode should be skipped.
For example,
output shows in the terminal something like this test/boost/aggregate_fcts_test.cc::test_aggregate_avg.dev.
So to execute this specific test function, please use the next command
pytest --mode dev test/boost/aggregate_fcts_test.cc::test_aggregate_avg
Writing tests
Because of the large build time and build size of each separate test executable, it is recommended to put test functions into relatively large source files. But not too large - to keep compilation time of a single source file (during development) at reasonable levels.
When adding new source files in test/boost, don't forget to list the new source file in configure.py and also in CMakeLists.txt. The former is needed by our CI, but the latter is preferred by some developers.