The Database object manages connections to an SQL database, in which the current ledger state and several auxiliary tables are stored. The database object also caches prepared statements, and holds some timers for tracking query performance.
Database connections are configured by the config variable DATABASE, see src/main/Config.h
The connections and statements are of the types provided by the
SOCI database access library, a copy of which
is contained in the lib/soci subdirectory of the
stellar-core source tree and built along with it.