In some cases estimated number of partitions can be 0, which is albeit a
legit estimation result, breaks many low-level sstable writer code, so
some of these have assertions to ensure estimated partitions is > 0.
To avoid hitting this assert all users of the sstable writers do the
clamping, to ensure estimated partitions is at least 1. However leaving
this to the callers is error prone as #6913 has shown it. As this
clamping is standard practice, it is better to do it in the writers
themselves, avoiding this problem altogether. This is exactly what this
patch does. It also adds two unit tests, one that reproduces the crash
in #6913, and another one that ensures all sstable writers are fine with
estimated partitions being 0 now. Call sites previously doing the
clamping are changed to not do it, it is unnecessary now as the writer
does it itself.
Fixes#6913
Tests: unit(dev)
Signed-off-by: Botond Dénes <bdenes@scylladb.com>
Message-Id: <20200724120227.267184-1-bdenes@scylladb.com>
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