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From "Dan Blum" <>
Subject RE: Modify Keys within iterator
Date Fri, 30 Sep 2016 17:31:39 GMT
What code are you using to test the iterator, where you see no output?


From: Yamini Joshi [] 
Sent: Friday, September 30, 2016 1:26 PM
Subject: Modify Keys within iterator


Hello Everyone!

I am trying to write an iterator to modify keys within a table (at scan). My use case is to
select a few records that match a certain criterion and then modify them within the iterator(using
the following class) for some other succeeding iterator/combiner. The problem is that this
iterator does return any records/keys. I added some primitive prints and found that the keys
(this.key) is changed but the output of iterator is nothing. I'd appreciate if someone could
give me any insight. I'm sure I'm making a teeny tiny mistake somewhere.


         row                   colF                       colQ                 ts        

I/P:    r_1                   f                             f_1                          

         r_1                   fx                            f_1                         

O/P:  f_1                   r                             r_1                            

         f_1                   fx                            fx                          


public class KeyModifyIterator implements SortedKeyValueIterator<Key,Value> {

  private SortedKeyValueIterator<Key,Value> source;
  private Key key;
  private Value value;

  public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String>
options, IteratorEnvironment env) throws IOException {
    this.source = source;

  public boolean hasTop() {
    return key != null;

  public void next() throws IOException {
        if (source.hasTop()) {
            ByteSequence currentRow = source.getTopKey().getRowData();
            ByteSequence currentColf = source.getTopKey().getColumnFamilyData();
            ByteSequence currentColq = source.getTopKey().getColumnQualifierData();
            long ts = source.getTopKey().getTimestamp();
            String v = source.getTopValue().toString();
            System.out.println("Key = " + currentRow.toString() + " Cf = " + currentColf.toString()
+ " Cq = " + currentColq.toString()  + " val = " + v.toString());
            if (currentColf.toString().equals("fx")){
                System.out.println("Updating fx" );
                this.key = new Key(currentColq.toArray(), currentColf.toArray(), currentColf.toArray(),
new byte[0], ts);
                this.value = new Value (v.getBytes(UTF_8));
                System.out.println("Updating other" );
                this.key = new Key(currentColq.toArray(), "r".getBytes(UTF_8), currentRow.toArray(),
new byte[0], ts);                
                this.value = new Value (v.getBytes(UTF_8));
          } else {
            this.key = null;
            this.value = null;

  public void seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive)
throws IOException {, columnFamilies, inclusive);

  public Key getTopKey() {
    return key;

  public Value getTopValue() {
    return value;

  public SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env) {
    return null;


Best regards,
Yamini Joshi

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