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From geraldss <...@git.apache.org>
Subject [GitHub] phoenix pull request #308: Client-side hash aggregation
Date Sat, 21 Jul 2018 00:02:30 GMT
Github user geraldss commented on a diff in the pull request:

    https://github.com/apache/phoenix/pull/308#discussion_r204193333
  
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/iterate/ClientHashAggregatingResultIterator.java
---
    @@ -0,0 +1,189 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you 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.
    + */
    +package org.apache.phoenix.iterate;
    +
    +import static org.apache.phoenix.query.QueryConstants.AGG_TIMESTAMP;
    +import static org.apache.phoenix.query.QueryConstants.SINGLE_COLUMN;
    +import static org.apache.phoenix.query.QueryConstants.SINGLE_COLUMN_FAMILY;
    +
    +import java.io.IOException;
    +import java.sql.SQLException;
    +import java.util.ArrayList;
    +import java.util.Collections;
    +import java.util.HashMap;
    +import java.util.Iterator;
    +import java.util.List;
    +import java.util.Map;
    +import java.util.Objects;
    +
    +import org.apache.hadoop.hbase.Cell;
    +import org.apache.hadoop.hbase.KeyValue;
    +import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
    +import org.apache.phoenix.compile.StatementContext;
    +import org.apache.phoenix.expression.Expression;
    +import org.apache.phoenix.expression.aggregator.Aggregator;
    +import org.apache.phoenix.expression.aggregator.Aggregators;
    +import org.apache.phoenix.memory.MemoryManager.MemoryChunk;
    +import org.apache.phoenix.schema.tuple.MultiKeyValueTuple;
    +import org.apache.phoenix.schema.tuple.Tuple;
    +import org.apache.phoenix.util.KeyValueUtil;
    +import org.apache.phoenix.util.SizedUtil;
    +import org.apache.phoenix.util.TupleUtil;
    +
    +/**
    + * 
    + * This class implements client-side hash aggregation in memory.
    + * Issue https://issues.apache.org/jira/browse/PHOENIX-4751.
    + * 
    + */
    +public class ClientHashAggregatingResultIterator
    +    implements AggregatingResultIterator {
    +
    +    private static final int HASH_AGG_INIT_SIZE = 64*1024;
    +    private static final int CLIENT_HASH_AGG_MEMORY_CHUNK_SIZE = 64*1024;
    +    private static final byte[] UNITIALIZED_KEY_BUFFER = new byte[0];
    +    private final ResultIterator resultIterator;
    +    private final Aggregators aggregators;
    +    private final List<Expression> groupByExpressions;
    +    private final int thresholdBytes;
    +    private final MemoryChunk memoryChunk;
    +    private HashMap<ImmutableBytesWritable, Aggregator[]> hash;
    +    private List<ImmutableBytesWritable> keyList;
    +    private Iterator<ImmutableBytesWritable> keyIterator;
    +
    +    public ClientHashAggregatingResultIterator(StatementContext context, ResultIterator
resultIterator, Aggregators aggregators,
    +                                               List<Expression> groupByExpressions,
int thresholdBytes) {
    +
    +        Objects.requireNonNull(resultIterator);
    +        Objects.requireNonNull(aggregators);
    +        Objects.requireNonNull(groupByExpressions);
    +        this.resultIterator = resultIterator;
    +        this.aggregators = aggregators;
    +        this.groupByExpressions = groupByExpressions;
    +        this.thresholdBytes = thresholdBytes;
    +        memoryChunk = context.getConnection().getQueryServices().getMemoryManager().allocate(CLIENT_HASH_AGG_MEMORY_CHUNK_SIZE);
    +    }
    +
    +    @Override
    +        public Tuple next() throws SQLException {
    +        if (keyIterator == null) {
    +            hash = populateHash();
    +            keyList = sortKeys();
    --- End diff --
    
    I tried avoiding the sort, but could not make the code work without it. In my use case,
if there's an ORDER BY after the groups, and the ORDER BY was by primary key, it was not being
applied. If the ORDER BY was not by primary key, it was being applied.
    
    I left this sort in because (1) it introduces no error; (2) the sorting is after the grouping,
so more efficient than the current solution, which sorts before the grouping; (3) it avoids
the problem above.


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