7ada7f2bf9
- Handle dropped tables gracefully in the tablet load balancer's `get_schema_and_rs()` instead of aborting with `on_internal_error`
- The load balancer operates on a token metadata snapshot but accesses the live schema for table lookups. A DROP TABLE applied by another fiber between coroutine yield points can remove a table from the live schema while it still exists in the snapshot, causing an abort.
`get_schema_and_rs()` now returns `std::optional` and logs a warning in debug log level instead of aborting when a table is missing. All callers skip dropped tables:
- `make_sizing_plan`: skips to next table
- `make_resize_plan`: skips to next table (merge suppression is moot)
- `check_constraints`: returns `skip_info{}` with empty viable targets
- `get_rs`: returns `nullptr`, checked by `check_constraints`
The call chain is: `make_plan` → `make_internode_plan` → `check_constraints` → `get_rs` → `get_schema_and_rs`. The `make_internode_plan` coroutine has multiple `co_await` yield points (`maybe_yield`, `pick_candidate`) between building the candidate tablet list and checking replication constraints. A DROP TABLE schema mutation applied during any of these yields removes the table from `_db.get_tables_metadata()` while the candidate list still references it.
Added `test_load_balancing_with_dropped_table` which simulates the race by capturing a token metadata snapshot, dropping the table, then calling `balance_tablets` with the stale snapshot.
Fixes: SCYLLADB-1906
This fix needs to be backported to versions: 2025.4, 2026.1
- (cherry picked from commit 4375b502ea)
- (cherry picked from commit be56bf031f)
Parent PR: #29585
Closes scylladb/scylladb#29883
* github.com:scylladb/scylladb:
test: verify load balancer handles dropped tables gracefully
tablet_allocator: handle dropped tables gracefully in get_schema_and_rs
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