* the valid bucket ords for which deferred collection should be
* attempted
*/
public void prepareSelectedBuckets(long... survivingBucketOrds) {
BucketCollector subs = new BucketCollector() {
@Override
public void setNextReader(LeafReaderContext reader) {
// Need to set AggregationContext otherwise ValueSources in aggs
// don't read any values
context.setNextReader(reader);