sqlite3_db_release_memory —
Free Memory Used By A Database Connection
int
sqlite3_db_release_memory(sqlite3*);
The sqlite3_db_release_memory(D) interface attempts to free as much heap memory
  as possible from database connection D. Unlike the sqlite3_release_memory()
  interface, this interface is in effect even when the
  SQLITE_ENABLE_MEMORY_MANAGEMENT compile-time option is omitted.