Method scanMeta

src/HBaseClient.java:2902–2952

Later versions of HBase dropped the old RegionClient#getClosestRowBefore(RegionInfo, byte[], byte[], byte[]) method and switched to performing reverse scans. This method will handle the scanning returning either a meta row if found or an empty array if the row/table was not found. TODO - nee

(final RegionClient client, 
                                                 final RegionInfo region, 
                                                 final byte[] table, 
                                                 final byte[] row, 
                                                 final byte[] family)

   * exist. Or an exception if something goes pear shaped.
   */
  Deferred<ArrayList<KeyValue>> scanMeta(final RegionClient client, 
                                                 final RegionInfo region, 
                                                 final byte[] table, 
                                                 final byte[] row, 
                                                 final byte[] family) {
    final Scanner scanner = newScanner(table);
    scanner.setReversed(true);
    scanner.setMaxNumRows(1);
    scanner.setStartKey(row);
    scanner.setFamily(family);
    scanner.setRegionName(region);
    
    final Deferred<ArrayList<KeyValue>> deferred = 
        new Deferred<ArrayList<KeyValue>>();
    
    class ErrorCB implements Callback<Object, Exception> {
      @Override
      public Object call(final Exception ex) throws Exception {
        scanner.close();
        deferred.callback(ex);
        return null;
      }
      @Override
      public String toString() {
        return "scanMeta.ErrorCB";
      }
    }
    
    class MetaScanCB implements Callback<Void, ArrayList<ArrayList<KeyValue>>> {
      @Override
      public Void call(final ArrayList<ArrayList<KeyValue>> rows)
          throws Exception {
        final ArrayList<KeyValue> row = (rows == null || rows.isEmpty()) 
            ? new ArrayList<KeyValue>(0) : rows.get(0);
        scanner.close();
        deferred.callback(row);
        return null;
      }
      @Override
      public String toString() {
        return "scanMeta.MetaScanCB";
      }
    }
    
    HBaseRpc open_request = scanner.getOpenRequestForReverseScan(row);
    open_request.region = region;
    open_request.getDeferred().addCallbackDeferring(scanner.opened_scanner)
      .addCallbacks(new MetaScanCB(), new ErrorCB());
    client.sendRpc(open_request);
    return deferred;
  }
  
  /**
   * Callback executed when a lookup in META completes