real leveldb is better in lot of areas:
L0 are 1/10 of L1 sstable size
tables can be promoted to upper levels if no merging is needed (there is
hole)
variable number of sstables per level, but it tries to keep 1:10:100
sstable ratios. Not hard requirement
very important - better hash function. murmur and md5 hashes are
unsuitable for ldb because it turns key sequence into more or less
random noise. Changing hash function to leveldb one gives about 8 times
speed increase during seq. writes because far less table merges is needed
better merge policy: merge 1 table + up to 10 tables from next level
into next + 2 level.
