Yes, LSMT is a good example of pushing the idea of a hybrid append log and in memory data structure further. However, LSMT is for relatively smaller data set,

Yes, LSMT is a good example of pushing the idea of a hybrid append log and in memory data structure further. However, LSMT is for relatively smaller data set, i.e. ordered key-value. It has worse write amplification than a simple append log. The level-0 memtable flushed to the write-ahead-log counts as one write. Writing to the level-1 sorted files counts as 2nd write. Merging the sorted files counts as 3rd write. There're 2~3 writes per change. Also it doesn't offer help to address the frequent update block problem. All versions of a data change are written to disk. A merge is needed to get rid of the old versions. But it has a number of good implementation ideas that can be borrowed.