SSTables that contain many keys - a common case with small partitions in
long lived nodes - can generate filters that are quite large.
I have seen stalls over 80ms when reading a filter that was the result
of a 6h write load of very small keys after nodetool compact (filter was
in the 100s of MB)
Similar care should be taken when creating the filter, as if the
estimated number of partitions is big, the resulting large_bitset can be
quite big as well.
If we treat the i_filter.hh and large_bitset.hh interfaces as truly
generic, then maybe we should have an in_thread version along with a
common version. But the bloom filter is the only user for both and even
if that changes in the future, it is still a good idea to run something
with a massive loop in a thread.
So for simplicity, I am just asserting that we are on a thread to avoid
surprises, and inserting preemption points in the loops.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
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