00409b61f1
This PR introduces the vnodes-to-tablets migration procedure, which enables converting an existing vnode-based keyspace to tablets.
The migration is implemented as a manual, operator-driven process executed in several stages. The core idea is to first create tablet maps with the same token boundaries and replica hosts as the vnodes, and then incrementally convert the storage of each node to the tablets layout. At a high level, the procedure is the following:
1. Create tablet maps for all tables in the keyspace.
2. Sequentially upgrade all nodes from vnodes to tablets:
1. Mark a node for upgrade in the topology state.
2. Restart the node. During startup, while the node is offline, it reshards the SSTables on vnode boundaries and switches to a tablet ERM.
3. Wait for the node to return online before proceeding to the next node.
4. Finalize the migration:
1. Update the keyspace schema to mark it as tablet-based.
2. Clear the group0 state related to the migration.
From the client's perspective, the migration is online; the cluster can still serve requests on that keyspace, although performance may be temporarily degraded.
During the migration, some nodes use vnode ERMs while others use tablet ERMs. Cluster-level algorithms such as load balancing will treat the keyspace's tables as vnode-based. Once migration is finalized, the keyspace is permanently switched to tablets and cannot be reverted back to vnodes. However, a rollback procedure is available before finalization.
The patch series consists of:
* Load balancer adjustments to ignore tablets belonging to a migrating keyspace.
* A new vnode-based resharding mode, where SSTables are segregated on vnode boundaries rather than with the static sharder.
* A new per-node `intended_storage_mode` column in `system.topology`. Represents migration intent (whether migration should occur on restart) and direction.
* Four new REST endpoints for driving the migration (start, node upgrade/downgrade, finalize, status), along with `nodetool` wrappers. The finalization is implemented as a global topology request.
* Wiring of the migration process into the startup logic: the `distributed_loader` determines a migrating table's ERM flavor from the `intended_storage_mode` and the ERM flavor determines the `table_populator`'s resharding mode. Token metadata changes have been adjusted to preserve the ERM flavor.
* Cluster tests for the migration process.
Fixes SCYLLADB-722.
Fixes SCYLLADB-723.
Fixes SCYLLADB-725.
Fixes SCYLLADB-779.
Fixes SCYLLADB-948.
New feature, no backport is needed.
Closes scylladb/scylladb#29065
* github.com:scylladb/scylladb:
docs: Add ops guide for vnodes-to-tablets migration
test: cluster: Add test for migration of multiple keyspaces
test: cluster: Add test for error conditions
test: cluster: Add vnodes->tablets migration test (rollback)
test: cluster: Add vnodes->tablets migration test (1 table, 3 nodes)
test: cluster: Add vnodes->tablets migration test (1 table, 1 node)
scylla-nodetool: Add migrate-to-tablets subcommand
api: Add REST endpoint for vnode-to-tablet migration status
api: Add REST endpoint for migration finalization
topology_coordinator: Add `finalize_migration` request
database: Construct migrating tables with tablet ERMs
api: Add REST endpoint for upgrading nodes to tablets
api: Add REST endpoint for starting vnodes-to-tablets migration
topology_state_machine: Add intended_storage_mode to system.topology
distributed_loader: Wire vnode-based resharding into table populator
replica: Pick any compaction group for resharding
compaction: resharding_compaction: add vnodes_resharding option
storage_service: Preserve ERM flavor of migrating tables
tablet_allocator: Exclude migrating tables from load balancing
feature_service: Add vnodes_to_tablets_migrations feature
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.