We are currently suspecting that the bloom filter false positive ratio
is not being respected. While trying to debug that, I found out that we
have a more basic problem:
The numbers are all meaningless, because the stats are wrong. We are
accumulating by summing the ratios together. It's easy to see how this
doesn't work, if we look at an example where the ratio for some CFs is
zero:
SST1: false = 1, total = 2. ratio = 0.5
SST2: false = 0, total = 98 . ratio = 0.
The real ratio in this example is 1 / (98 + 2) = 1 %, but the displayed
ratio will be 0.5 + 0 = 0.5.
This patch will map reduce all the sstables together keeping both
numerator and denominator, yielding the right value at the end. To do
that, we'll reuse the existing ratio_holder class, which already does
exactly what we want.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
Message-Id: <20170518222333.16307-1-glauber@scylladb.com>
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