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6fb37ae77f
Scylla implements `LWT` in the` storage_proxy::cas` method. This method expects to be called on a specific shard, represented by the `cas_shard` parameter. Clients must create this object before calling `storage_proxy::cas`, check its `this_shard()` method, and jump to `cas_shard.shard()` if it returns false. The nuance is that by the time the request reaches the destination shard, the tablet may have already advanced in its migration state machine. For example, a client may acquire a `cas_shard` at the `streaming` tablet state, then submit a request to another shard via `smp::submit_to(cas_shard.shard())`. However, the new `cas_shard` created on that other shard might already be in the `write_both_read_new` state, and its `cas_shard.shard()` would not be equal to `this_shard_id()`. Such broken invariant results in an `on_internal_error` in `storage_proxy::cas`. Clients of `storage_proxy::cas` are expected to check` cas_shard.this_shard()` and recursively jump to another shard if it returns false. Most calls to `storage_proxy::cas` already implement this logic. The only exception is `executor::do_batch_write`, which currently checks `cas_shard.this_shard()` only once. This can break the invariant if the tablet state changes more than once during the operation. This PR fixes the issue by implementing recursive `cas_shard.this_shard()` checks in `executor::do_batch_write`. It also adds a test that reproduces the problem. Fixes: scylladb/scylladb#27353 backport: need to be backported to 2025.4 - (cherry picked from commite60bcd0011) - (cherry picked from commit74bf24a4a7) - (cherry picked from commit9bef142328) - (cherry picked from commitc6eec4eeef) - (cherry picked from commit3a865fe991) - (cherry picked from commit0bcc2977bb) - (cherry picked from commit608eee0357) Parent PR: #27396 Closes scylladb/scylladb#27529 * github.com:scylladb/scylladb: alternator/executor.cc: eliminate redundant dk copy alternator/executor.cc: release cas_shard on the original shard alternator/executor.cc: move shard check into cas_write alternator/executor.cc: make cas_write a private method alternator/executor.cc: make do_batch_write a private method alternator/executor.cc: fix indent test_alternator: add test_alternator_invalid_shard_for_lwt alternator/executor.cc: avoid cross-shard free