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2c181b69c9
The reason sstable key estimation is inaccurate is that it doesn't account that
index sampling is now dynamic.
The estimation is done as follow:
uint64_t get_estimated_key_count() const {
return ((uint64_t)_components->summary.header.size_at_full_sampling + 1) *
_components->summary.header.min_index_interval;
}
The biggest problem is that _components->summary.header.min_index_interval isn't
actually the minimum interval, but instead the default interval value set in the
schema.
So the estimation gets worse the larger the average partition, because the larger
the average partition the lower the index sampling interval.
One of the problems is that estimation has a big influence on bloom filter size,
and so for large partitions we were generating bigger filters than we had to.
From now on, size at full sampling is calculated as if sampling were static
(which was the case until commit 8726ee937d which introduced size-based
sampling), using minimum index as a strict sampling interval.
Tests: units (release)
Fixes #3113.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20180122233612.11147-1-raphaelsc@scylladb.com>