"
Today, both operations are picking the highest level as the ideal level for
placing the output, but the size of input should be used instead.
The formula for calculating the ideal level is:
ceil(log base(fan_out) of (total_input_size / max_fragment_size))
where fan_out = 10 by default,
total_input_size = total size of input data and
max_fragment_size = maximum size for fragment (160M by default)
such that 20 fragments will be placed at level 2, as level 1
capacity is 10 fragments only.
By placing the output in the incorrect level, tons of backlog will be generated
for LCS because it will either have to promote or demote fragments until the
levels are properly balanced.
"
* 'optimize_lcs_major_and_reshape/v2' of https://github.com/raphaelsc/scylla:
compaction: LCS: avoid needless work post major compaction completion
compaction: LCS: avoid needless work post reshape completion
compaction: LCS: extract calculation of ideal level for input
compaction: LCS: Fix off-by-one in formula used to calculate ideal level
53c66fe24a