mirror of
https://github.com/scylladb/scylladb.git
synced 2026-04-20 00:20:47 +00:00
f06094aa95
Yet another barrier-failure scenario exists in the `write_both_read_new` state. When the barrier fails, the tablet is expected to transition to `cleanup_target`, but because barrier execution is asynchronous, the cleanup transition can be skipped entirely and the tablet may continue forward instead. Both `write_both_read_new` and `cleanup_target` modify read and write selectors. In this situation, a barrier is required, and transitioning directly between these states without one is unsafe. Introduce an intermediate `write_both_read_old_fallback_cleanup` state that modifies only a read selector and can be entered without a barrier (there is no need to wait for all nodes to start using the "new" read selector). From there, the tablet can proceed to `cleanup_target`, where the required barriers are enforced. This also avoids changing both selectors in a single step. A direct transition from `write_both_read_new` to `cleanup_target` updates both selectors at once, which can leave coordinators using the old selector for writes and the new selector for reads, causing reads to miss preceding writes. By routing through the fallback state, selectors are updated in order—read first, then write—preserving read-after-write correctness.