HBase Aggregation - hadoop

Question

I'm having some trouble doing aggregation on a particular column in HBase.
This is the snippet of code I tried:
Configuration config = HBaseConfiguration.create();
AggregationClient aggregationClient = new AggregationClient(config);
Scan scan = new Scan();
scan.addColumn(Bytes.toBytes("drs"), Bytes.toBytes("count"));
ColumnInterpreter<Long, Long> ci = new LongColumnInterpreter();
Long sum = aggregationClient.sum(Bytes.toBytes("DEMO_CALCULATIONS"), ci , scan);
System.out.println(sum);
sum returns a value of null.
The aggregationClient API works fine if I do a rowcount.
I was trying to follow the directions in http://michaelmorello.blogspot.in/2012/01/row-count-hbase-aggregation-example.html
Could there be a problem with me using a LongColumnInterpreter when the 'count' field was an int? What am I missing in here?

Answer 1

You can only use long(8bytes) to do sum with default setting.
Cause in the code of AggregateImplementation's getSum method, it handle all the returned KeyValue as long.
List<KeyValue> results = new ArrayList<KeyValue>();
try {
boolean hasMoreRows = false;
do {
hasMoreRows = scanner.next(results);
for (KeyValue kv : results) {
temp = ci.getValue(colFamily, qualifier, kv);
if (temp != null)
sumVal = ci.add(sumVal, ci.castToReturnType(temp));
}
results.clear();
} while (hasMoreRows);
} finally {
scanner.close();
}
and in LongColumnInterpreter
public Long getValue(byte[] colFamily, byte[] colQualifier, KeyValue kv)
throws IOException {
if (kv == null || kv.getValueLength() != Bytes.SIZEOF_LONG)
return null;
return Bytes.toLong(kv.getBuffer(), kv.getValueOffset());
}