readdb is an alias for org.apache.nutch.db.WebDBReader
The WebDBReader implements all the read-only parts of accessing our web database. All the writing ones can be found in WebDBWriter.
Usage: bin/nutch org.apache.nutch.db.WebDBReader (-local | -ndfs <namenode:port>) <db> [-pageurl url] | [-pagemd5 md5] | [-dumppageurl] | [-dumppagemd5] | [-toppages <k>] | [-linkurl url] | [-linkmd5 md5] | [-dumplinks] | [-stats]