Since 0.8 bitcoind uses LevelDB for the storage of the UTXO set in chainstate/
and the block index in blocks/index/
. On github special branch of LevelDB can be found:
https://github.com/bitcoin/leveldb
What reasons made LevelDB the best choice for key-value storage compared to other embedded database solutions? How does bitcoind's own LevelDB fork differ from the official version?