f3245c933d
- Fix intranode shard balancing to respect the size-based balance threshold, preventing unnecessary migrations when load difference between shards is negligible - Add a regression test that verifies the threshold is respected for intranode balancing The intranode shard balancing loop only stopped when the algorithm exhausted the migration candidates or when a migration would go against convergence (it would increase imbalance instead of decrease it). This caused unnecessary tablet migrations for negligible imbalances (e.g., 0.78% difference between shards). The inter-node balancer already uses `is_balanced()` to stop when the relative load difference is within the configured `size_based_balance_threshold`, but this check was missing from the intranode path. Apply the same `is_balanced()` threshold check that is already used for inter-node balancing to the intranode convergence loop. When the relative load difference between the most-loaded and least-loaded shards on a node is within the threshold, the balancer now stops without issuing further migrations. The test creates a single node with 2 shards and 512 tablets: 1. **Balanced scenario** (257 vs 255 tablets, same size): relative diff = 0.78% < 1% threshold → verifies no intranode migration is emitted 2. **Unbalanced scenario** (307 vs 205 tablets, same size): relative diff = 33% >> 1% threshold → verifies intranode migration IS emitted Fixes: SCYLLADB-2006 This is a performance improvement which reduces the number of intranode migrations issued, and needs to be backported to versions with size-based load balancing: 2026.1 and 2026.2 - (cherry picked from commitaaead10e5d) - (cherry picked from commit6856f51097) Parent PR: #29756 Closes scylladb/scylladb#29895 * github.com:scylladb/scylladb: test: add test for intranode balance threshold in size-based mode tablet_allocator: apply balance threshold to intranode shard balancing
Scylla in-source tests.
For details on how to run the tests, see docs/dev/testing.md
Shared C++ utils, libraries are in lib/, for Python - pylib/
alternator - Python tests which connect to a single server and use the DynamoDB API unit, boost, raft - unit tests in C++ cqlpy - Python tests which connect to a single server and use CQL topology* - tests that set up clusters and add/remove nodes cql - approval tests that use CQL and pre-recorded output rest_api - tests for Scylla REST API Port 9000 scylla-gdb - tests for scylla-gdb.py helper script nodetool - tests for C++ implementation of nodetool
If you can use an existing folder, consider adding your test to it. New folders should be used for new large categories/subsystems, or when the test environment is significantly different from some existing suite, e.g. you plan to start scylladb with different configuration, and you intend to add many tests and would like them to reuse an existing Scylla cluster (clusters can be reused for tests within the same folder).
To add a new folder, create a new directory, and then
copy & edit its suite.ini.