code: func (b *lowBuilder) dbName(of dbname) string {
  	unique := b.dbUnique()
  	if unique == "" {
  		log.Printf("Could not define uniqueness for database of %q. Do not use the same index DBMS with other Perkeep instances.", of)
  	}
  	if unique == useDBNamesConfig {
  		// this is the hint that we should revert to the old style DBNames, so this
  		// instance can reuse its existing databases
  		return b.oldDBNames(of)
  	}
  	prefix := "pk_"
  	if unique != "" {
  		prefix += unique + "_"
  	}
  	switch of {
  	case dbIndex:
  		if b.high.DBName != "" {
  			return b.high.DBName
  		}
  		return prefix + "index"
  	case dbBlobpackedIndex:
  		return prefix + "blobpacked"
  	case dbDiskpackedIndex:
  		return prefix + "diskpacked"
  	case dbUIThumbcache:
  		return prefix + "uithumbmeta"
  	}
  	asString := string(of)
  	if strings.HasPrefix(asString, string(dbSyncQueue)) {
  		return prefix + "syncto_" + strings.TrimPrefix(asString, string(dbSyncQueue))
  	}
  	return ""
  }
docs: // dbName returns which database to use for the provided user ("of"), which can
  // only be one of the const defined above. Returned values all follow the same name
  // scheme for consistency:
  // -prefixed with "pk_", so as to distinguish them from databases for other programs
  // -followed by a username-based uniqueness string
  // -last part says which component/part of perkeep it is about