The leveling here reminds me a bit of how Lucene organizes and compacts its segments files. When you write documents to Lucene they are written to a segments f

The leveling here reminds me a bit of how Lucene organizes and compacts its segments files. When you write documents to Lucene they are written to a segments file, usually one for each batch of documents you write. When searching, each of the segments files are searched for terms, so the more segments files you have, the slower the search tends to be. When segments files reach a certain size they are automatically compacted into other segments files. Users can (and should) then "optimize" their index, which compacts all the segments files into a single file. The log files and sorted tables of leveldb appear to work very similarly.