code: func (db *DB) dropFrozenMem() {
  	db.memMu.Lock()
  	if err := db.s.stor.Remove(db.frozenJournalFd); err != nil {
  		db.logf("journal@remove removing @%d %q", db.frozenJournalFd.Num, err)
  	} else {
  		db.logf("journal@remove removed @%d", db.frozenJournalFd.Num)
  	}
  	db.frozenJournalFd = storage.FileDesc{}
  	db.frozenMem.decref()
  	db.frozenMem = nil
  	db.memMu.Unlock()
  }
docs: // Drop frozen memdb; assume that frozen memdb isn't nil.