The single-key sstable reader uses the clustering ranges from the slice
to determine the upper bound of the disk read-range using the index.
For this is simply uses the end bound of the last clustering ranges. For
reverse reads however the clustering ranges in the slice are in reverse
order, so this will in fact be the upper bound of the smallest range.
Depending on whether the distance between the clustering range is big
enough for the sstable reader to use the index to skip between them,
this will lead to either reading too little data or an assert failure.
This patch fixes the problematic function `get_slice_upper_bound()` to
consider reverse reads as well.
Initially I thought there will be more mishandling of reverse slices,
but actually `mutation_fragment_filter`, the component doing the actual
slicing of rows, is already reverse-slice aware.
A unit test which reproduces the assert failure is also added.
Fixes: #6171
Signed-off-by: Botond Dénes <bdenes@scylladb.com>
Message-Id: <20200507114956.271799-1-bdenes@scylladb.com>
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