Raphael S. Carvalho 79958472bc replica: Fix range reads spanning sibling tablets ...

We don't guarantee that coordinators will only emit range reads that
span only one tablet.

Consider this scenario:

1) split is about to be finalized, barrier is executed, completes.
2) coordinator starts a read, uses pre-split erm (split not committed to group0 yet)
3) split is committed to group0, all replicas switch storage.
4) replica-side read is executed, uses a range which spans tablets.

We could fix it with two-phase split execution. Rather than pushing the
complexity to higher levels, let's fix incremental selector which should
be able to serve all the tokens owned by a given shard. During split
execution, either of sibling tablets aren't going anywhere since it
runs with state machine locked, so a single read spanning both
sibling tablets works as long as the selector works across tablet
boundaries.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
(cherry picked from commit 53df911145)

2025-06-15 09:14:38 -03:00

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