The ledger system in Hyperledger fabric uses levelDB. By definition, LevelDB allows concurrent

writers to safely insert data into the database by providing internal synchronization. LevelDB uses

very coarse-grained synchronization which forces all writes to proceed in an ordered, first-come-first-

served basis, effectively reduces throughput to a single thread. State database options include

LevelDB and CouchDB. LevelDB is the default key-value state database embedded in the peer

process. CouchDB is an optional alternative external state database. Like the LevelDB key-value store,

CouchDB can store any binary data that is modeled in chaincode (CouchDB attachment functionality

is used internally for non-JSON binary data). But as a JSON document store, CouchDB additionally

enables rich query against the chaincode data, when chaincode values (e.g. assets) are modeled as

JSON data.