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7b80816721
On short-pages, cut short because of a tombstone prefix.
When page-results are filtered and the filter drops some rows, the
last-position is taken from the page visitor, which does the filtering.
This means that last partition and row position will be that of the last
row the filter saw. This will not match the last position of the
replica, when the replica cut the page due to tombstones.
When fetching the next page, this means that all the tombstone suffix of
the last page, will be re-fetched. Worse still: the last position of the
next page will not match that of the saved reader left on the replica, so
the saved reader will be dropped and a new one created from scratch.
This wasted work will show up as elevated tail latencies.
Fix by always taking the last position from raw query results.
Fixes: #22620
Closes scylladb/scylladb#22622
(cherry picked from commit 7ce932ce01)
Closes scylladb/scylladb#22717