[GitHub] spark pull request #18468: [SPARK-20783][SQL] Create CachedBatchColumnVector...

[cloud-fan <gi...@git.apache.org>]

Github user cloud-fan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/18468#discussion_r128231184
  
    --- Diff: sql/core/src/main/java/org/apache/spark/sql/execution/vectorized/CachedBatchColumnVector.java ---
    @@ -0,0 +1,407 @@
    +/*
    + * 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.spark.sql.execution.vectorized;
    +
    +import java.nio.ByteBuffer;
    +
    +import org.apache.spark.memory.MemoryMode;
    +import org.apache.spark.sql.execution.columnar.*;
    +import org.apache.spark.sql.types.*;
    +import org.apache.spark.unsafe.types.UTF8String;
    +
    +/**
    + * A column backed by data compressed thru ColumnAccessor
    + * this is a wrapper to read compressed data for table cache
    + */
    +public final class CachedBatchColumnVector extends ColumnVector {
    +
    +  // accessor for a column
    +  private ColumnAccessor columnAccessor;
    +
    +  // a row where the compressed data is extracted
    +  private ColumnVector columnVector;
    +
    +  // an accessor uses only row 0 in columnVector
    +  private final int ROWID = 0;
    +
    +  // Keep row id that was previously accessed
    +  private int previousRowId = -1;
    +
    +
    +  public CachedBatchColumnVector(byte[] buffer, int numRows, DataType type) {
    +    super(numRows, DataTypes.NullType, MemoryMode.ON_HEAP);
    +    initialize(buffer, type);
    +    reserveInternal(numRows);
    +    reset();
    +  }
    +
    +  @Override
    +  public long valuesNativeAddress() {
    +    throw new RuntimeException("Cannot get native address for on heap column");
    +  }
    +  @Override
    +  public long nullsNativeAddress() {
    +    throw new RuntimeException("Cannot get native address for on heap column");
    +  }
    +
    +  @Override
    +  public void close() {
    +  }
    +
    +  // call extractTo() for rowId only once before getting actual data
    +  private void prepareAccess(int rowId) {
    +    if (previousRowId == rowId) {
    +      // do nothing
    +    } else if (previousRowId < rowId) {
    +      for (int i = previousRowId + 1; i <= rowId; i++) {
    +        assert (columnAccessor.hasNext());
    +        columnAccessor.extractTo(columnVector, ROWID);
    --- End diff --
    
    Can we keep the value in `MutableUnsafeRow` instead of `ColumnVector`? Then we don't need to change `ColumnAccessor` to support `ColumnVector`.


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