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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-2417) Compress memory used by row key byte[] of guideposts
Date Sun, 17 Jan 2016 00:34:40 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-2417?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15103520#comment-15103520
] 

ASF GitHub Bot commented on PHOENIX-2417:
-----------------------------------------

Github user JamesRTaylor commented on a diff in the pull request:

    https://github.com/apache/phoenix/pull/147#discussion_r49939300
  
    --- Diff: phoenix-core/src/main/java/org/apache/phoenix/schema/stats/GuidePostsInfoWriter.java
---
    @@ -0,0 +1,129 @@
    +/*
    + * 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.schema.stats;
    +
    +import java.io.DataOutputStream;
    +import java.io.IOException;
    +
    +import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
    +import org.apache.hadoop.hbase.util.Bytes;
    +import org.apache.phoenix.util.ByteUtil;
    +import org.apache.phoenix.util.CodecUtils;
    +import org.apache.phoenix.util.PrefixByteEncoder;
    +import org.apache.phoenix.util.TrustedByteArrayOutputStream;
    +
    +/*
    + * Writer to help in writing guidePosts and creating guidePostInfo. This is used when
we are collecting stats or reading stats for a table.
    + */
    +
    +public class GuidePostsInfoWriter {
    +    private PrefixByteEncoder encoder;
    +    private byte[] lastRow;
    +    private ImmutableBytesWritable guidePosts=new ImmutableBytesWritable(ByteUtil.EMPTY_BYTE_ARRAY);
    +    private long byteCount = 0;
    +    private int guidePostsCount;
    +    
    +    /**
    +     * The rowCount that is flattened across the total number of guide posts.
    +     */
    +    private long rowCount = 0;
    +    
    +    /**
    +     * Maximum length of a guidePost collected
    +     */
    +    private int maxLength;
    +    private DataOutputStream output;
    +    private TrustedByteArrayOutputStream stream;
    +    
    +    public final static GuidePostsInfo EMPTY_GUIDEPOST = new GuidePostsInfo(0,
    +            new ImmutableBytesWritable(ByteUtil.EMPTY_BYTE_ARRAY), 0, 0, 0);
    +
    +    public int getMaxLength() {
    +        return maxLength;
    +    }
    +    public GuidePostsInfoWriter(){
    +        this.stream = new TrustedByteArrayOutputStream(1);
    +        this.output = new DataOutputStream(stream);
    +        this.encoder=new PrefixByteEncoder();
    +        lastRow = ByteUtil.EMPTY_BYTE_ARRAY;
    +    }
    +
    +    /**
    +     * The guide posts, rowCount and byteCount are accumulated every time a guidePosts
depth is
    +     * reached while collecting stats.
    +     * @param row
    +     * @param byteCount
    +     * @return
    +     * @throws IOException 
    +     */
    +    public boolean writeGuidePosts( byte[] row, long byteCount, long rowCount) {
    +        if (row.length != 0 && Bytes.compareTo(lastRow, row) < 0) {
    +            try {
    +                encoder.encode(output, row, 0, row.length);
    +                this.byteCount += byteCount;
    +                this.guidePostsCount++;
    +                this.maxLength = encoder.getMaxLength();
    +                this.rowCount += rowCount;
    +                lastRow = row;
    +                return true;
    +            } catch (IOException e) {
    +                return false;
    +            }
    +        }
    +        return false;
    +    }
    +    
    +    public boolean writeGuidePosts(byte[] row){
    +        return writeGuidePosts(row, 0, 0);
    +    }
    +
    +    public boolean writeGuidePosts(byte[] row, long byteCount){
    +        return writeGuidePosts(row, byteCount, 0);
    +    }
    +
    +    public void close() {
    +        CodecUtils.close(stream);
    +    }
    +
    +    public void incrementRowCount() {
    +        this.rowCount++;
    +    }
    +
    +    public long getByteCount() {
    --- End diff --
    
    Make the getters private if possible (otherwise leave as is)


> Compress memory used by row key byte[] of guideposts
> ----------------------------------------------------
>
>                 Key: PHOENIX-2417
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-2417
>             Project: Phoenix
>          Issue Type: Sub-task
>            Reporter: James Taylor
>            Assignee: Ankit Singhal
>             Fix For: 4.7.0
>
>         Attachments: PHOENIX-2417.patch, PHOENIX-2417_encoder.diff, PHOENIX-2417_v2_wip.patch
>
>
> We've found that smaller guideposts are better in terms of minimizing any increase in
latency for point scans. However, this increases the amount of memory significantly when caching
the guideposts on the client. Guidepost are equidistant row keys in the form of raw byte[]
which are likely to have a large percentage of their leading bytes in common (as they're stored
in sorted order. We should use a simple compression technique to mitigate this. I noticed
that Apache Parquet has a run length encoding - perhaps we can use that.



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