/*
* Copyright 1999-2015 dangdang.com.
* <p>
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* </p>
*/
package com.dangdang.ddframe.rdb.sharding.merger.pipeline.reducer;
import com.dangdang.ddframe.rdb.sharding.merger.ResultSetMergeContext;
import com.dangdang.ddframe.rdb.sharding.merger.resultset.delegate.AbstractDelegateResultSet;
import com.dangdang.ddframe.rdb.sharding.merger.resultset.memory.row.OrderByResultSetRow;
import com.dangdang.ddframe.rdb.sharding.parser.result.merger.OrderByColumn;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Queue;
/**
* 流式排序的聚集结果集.
*
* @author gaohongtao
* @author zhangliang
*/
@Slf4j
public final class StreamingOrderByReducerResultSet extends AbstractDelegateResultSet {
private final Queue<ResultSetOrderByWrapper> delegateResultSetQueue;
private final List<OrderByColumn> orderByKeys;
public StreamingOrderByReducerResultSet(final ResultSetMergeContext resultSetMergeContext) throws SQLException {
super(resultSetMergeContext.getShardingResultSets().getResultSets());
delegateResultSetQueue = new PriorityQueue<>(getResultSets().size());
orderByKeys = resultSetMergeContext.getCurrentOrderByKeys();
}
@Override
protected boolean firstNext() throws SQLException {
for (ResultSet each : getResultSets()) {
ResultSetOrderByWrapper wrapper = new ResultSetOrderByWrapper(each);
if (wrapper.next()) {
delegateResultSetQueue.offer(wrapper);
}
}
return doNext();
}
@Override
protected boolean afterFirstNext() throws SQLException {
ResultSetOrderByWrapper firstResultSet = delegateResultSetQueue.poll();
setDelegate(firstResultSet.delegate);
if (firstResultSet.next()) {
delegateResultSetQueue.offer(firstResultSet);
}
return doNext();
}
private boolean doNext() {
if (delegateResultSetQueue.isEmpty()) {
return false;
}
setDelegate(delegateResultSetQueue.peek().delegate);
log.trace("Chosen order by value: {}, current result set hashcode: {}", delegateResultSetQueue.peek().row, getDelegate().hashCode());
return true;
}
@RequiredArgsConstructor
private class ResultSetOrderByWrapper implements Comparable<ResultSetOrderByWrapper> {
private final ResultSet delegate;
private OrderByResultSetRow row;
boolean next() throws SQLException {
boolean result = delegate.next();
if (result) {
row = new OrderByResultSetRow(delegate, orderByKeys);
}
return result;
}
@Override
public int compareTo(final ResultSetOrderByWrapper o) {
return row.compareTo(o.row);
}
}
}