sstable: method for estimating number of partitions in sstable
sstable: method for estimating number of partitions in sstable

The sstable has a lot of data, but suprisingly, and accurate count of the
number of partitions isn't available. We can get a good estimate by looking
at the number of summary entries.

Based on Origin's IndexSummary.getEstimatedKeyCount().

We need this estimate for compaction if we can't get (yet) a better
estimate from the cardinality estimator algorithm.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@cloudius-systems.com>

eklitzke/scylla,justintung/scylla,kjniemi/scylla,senseb/scylla,scylladb/scylla,bowlofstew/scylla,victorbriz/scylla,phonkee/scylla,tempbottle/scylla,shaunstanislaus/scylla,duarten/scylla,capturePointer/scylla,wildinto/scylla,rentongzhang/scylla,linearregression/scylla,wildinto/scylla,avikivity/scylla,raphaelsc/scylla,acbellini/scylla,capturePointer/scylla,respu/scylla,kjniemi/scylla,asias/scylla,stamhe/scylla,guiquanz/scylla,justintung/scylla,glommer/scylla,eklitzke/scylla,guiquanz/scylla,senseb/scylla,kangkot/scylla,shaunstanislaus/scylla,kangkot/scylla,rluta/scylla,dwdm/scylla,gwicke/scylla,avikivity/scylla,gwicke/scylla,rluta/scylla,respu/scylla,kangkot/scylla,bowlofstew/scylla,victorbriz/scylla,aruanruan/scylla,acbellini/scylla,bowlofstew/scylla,stamhe/scylla,duarten/scylla,rentongzhang/scylla,phonkee/scylla,scylladb/scylla,stamhe/scylla,duarten/scylla,kjniemi/scylla,asias/scylla,senseb/scylla,avikivity/scylla,aruanruan/scylla,asias/scylla,acbellini/scylla,victorbriz/scylla,wildinto/scylla,raphaelsc/scylla,rentongzhang/scylla,linearregression/scylla,capturePointer/scylla,dwdm/scylla,tempbottle/scylla,glommer/scylla,scylladb/scylla,phonkee/scylla,justintung/scylla,respu/scylla,tempbottle/scylla,rluta/scylla,eklitzke/scylla,aruanruan/scylla,scylladb/scylla,gwicke/scylla,guiquanz/scylla,dwdm/scylla,raphaelsc/scylla,glommer/scylla,linearregression/scylla,shaunstanislaus/scylla