Currently, database::truncate_table_on_all_shards calls the table::can_flush only on the coordinator shard
and therefore it may miss shards with dirty data if the coordinator shard happens to have empty memtables, leading to clearing the memtables with dirty data rather than flushing them.
This change fixes that by making flush safe to be called, even if the memtable list is empty, and calling it on every shard that can flush (i.e. seal_immediate_fn is engaged).
Also, change database_test::do_with_some_data is use random keys instead of hard-coded key names, to reproduce this issue with `snapshot_list_contains_dropped_tables`.
Fixes#27639
* The issue exists since forever and might cause data loss due to wrongly clearing the memtable, so it needs backport to all live versions
- (cherry picked from commit ec4069246d)
- (cherry picked from commit 5be6b80936)
- (cherry picked from commit 0342a24ee0)
- (cherry picked from commit 02ee341a03)
- (cherry picked from commit 2a803d2261)
- (cherry picked from commit 93b827c185)
- (cherry picked from commit ebd667a8e0)
Parent PR: #27643Closesscylladb/scylladb#28074
* https://github.com/scylladb/scylladb:
test: database_test: do_with_some_data: randomize keys
database: truncate_table_on_all_shards: drop outdated TODO comment
database: truncate_table_on_all_shards: consider can_flush on all shards
memtable_list: unify can_flush and may_flush
test: database_test: add test_flush_empty_table_waits_on_outstanding_flush
replica: table, storage_group, compaction_group: add needs_flush
test: database_test: do_with_some_data_in_thread: accept void callback function
7feafe9a62