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package com.salesforce.phoenix.iterate;
import java.sql.SQLException;
import java.util.List;
import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import com.salesforce.phoenix.expression.Expression;
import com.salesforce.phoenix.expression.OrderByExpression;
import com.salesforce.phoenix.schema.tuple.Tuple;
/**
*
* ResultIterator that does a merge sort on the list of iterators provided,
* returning the rows ordered by the OrderByExpression. The input
* iterators must be ordered by the OrderByExpression.
*
* @author jtaylor
* @since 0.1
*/
public class MergeSortTopNResultIterator extends MergeSortResultIterator {
private final int limit;
private int count = 0;
private final List<OrderByExpression> orderByColumns;
private final ImmutableBytesWritable ptr1 = new ImmutableBytesWritable();
private final ImmutableBytesWritable ptr2 = new ImmutableBytesWritable();
public MergeSortTopNResultIterator(ResultIterators iterators, Integer limit, List<OrderByExpression> orderByColumns) {
super(iterators);
this.limit = limit == null ? -1 : limit;
this.orderByColumns = orderByColumns;
}
@Override
protected int compare(Tuple t1, Tuple t2) {
for (int i = 0; i < orderByColumns.size(); i++) {
OrderByExpression order = orderByColumns.get(i);
Expression orderExpr = order.getExpression();
boolean isNull1 = !orderExpr.evaluate(t1, ptr1) || ptr1.getLength() == 0;
boolean isNull2 = !orderExpr.evaluate(t2, ptr2) || ptr2.getLength() == 0;
if (isNull1 && isNull2) {
continue;
} else if (isNull1) {
return order.isNullsLast() ? 1 : -1;
} else if (isNull2) {
return order.isNullsLast() ? -1 : 1;
}
int cmp = ptr1.compareTo(ptr2);
if (cmp == 0) {
continue;
}
return order.isAscending() ? cmp : -cmp;
}
return 0;
}
@Override
public Tuple peek() throws SQLException {
if (limit >= 0 && count >= limit) {
return null;
}
return super.peek();
}
@Override
public Tuple next() throws SQLException {
if (limit >= 0 && count++ >= limit) {
return null;
}
return super.next();
}
@Override
public void explain(List<String> planSteps) {
resultIterators.explain(planSteps);
planSteps.add(" SERVER TOP " + limit + " ROW" + (limit == 1 ? "" : "S") + " SORTED BY " + orderByColumns.toString());
planSteps.add("CLIENT MERGE SORT");
}
}