Advanced Appendix A: The LevelDB Internal Mechanics

Because Bitcoin Core relies so heavily on LevelDB for the chainstate and block index, an operator must understand how it works to optimize storage. LevelDB is a Log-Structured Merge-tree (LSM tree).

• Memtable: When Bitcoin writes a new UTXO, it first goes into a memory buffer called the Memtable. This is why dbcache is so important—it keeps this table in RAM.

• SSTables (Sorted String Tables): Once the Memtable is full, it is "Flushed" to the disk as a sorted file.

• Compaction: LevelDB periodically merges these files to remove old data. This is a CPU and Disk I/O intensive process. If your node suddenly slows down, it is likely performing a "Background Compaction."