DB header modification & b-tree block layer improvement & sequence number tree
- DB header is flushed for every commit commands. Dirty blocks will not be synchronized to file when the file is closed without commit.
- Small LRU cache has been added to b-tree block layer. B-tree nodes used for previous tree operations don't need to be re-read (memory copied) from file or buffer cache.
- Seq-tree has been fully functional.