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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-3913) Add per table sampling
Date Tue, 15 Sep 2015 14:15:46 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-3913?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14745522#comment-14745522
] 

ASF GitHub Bot commented on ACCUMULO-3913:
------------------------------------------

Github user keith-turner commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/46#discussion_r39514683
  
    --- Diff: core/src/main/java/org/apache/accumulo/core/compaction/CompactionSettings.java
---
    @@ -21,6 +21,7 @@
     
     public enum CompactionSettings {
     
    +  SF_NO_SAMPLE(new NullType()),
    --- End diff --
    
    >  Is that right?
    
    I think so.


> Add per table sampling
> ----------------------
>
>                 Key: ACCUMULO-3913
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-3913
>             Project: Accumulo
>          Issue Type: Improvement
>            Reporter: Keith Turner
>             Fix For: 1.8.0
>
>
> I am working on prototyping adding hash based sampling to Accumulo.  I am trying to accomplish
the following goals in the prototype.
>   # Have each RFile store a sample per locality group.  Also store the configuration
used to generate the sample.
>   # Use sampling functions that ensure the same row columns exist across the samples
in all RFiles. Hash mod is a good candidate that gives a random sample that's consistent across
files.
>   # Have scanners support scanning RFile's samples sets.  Scan should fail if RFiles
have different sample configuration.  Different sampling config implies the RFile's sample
sets contain a possibly disjoint set of row columns.
>   # Support generating sample data for RFiles generated for bulk import
>   # Support sample data in the memory map
>   # Support enabling and disabling sampling per table AND configuring a sample function.
> I am currently using the following function in my prototype to determine what data an
RFile stores in its sample set.  This code will always select same subset of rows for each
RFile's sample set.  I have not yet made the function configurable.
> {code:java}
> public class RowSampler implements Sampler {
>   private HashFunction hasher = Hashing.murmur3_32();
>   @Override
>   public boolean accept(Key k) {
>     ByteSequence row = k.getRowData();
>     HashCode hc = hasher.hashBytes(row.getBackingArray(), row.offset(), row.length());
>     return hc.asInt() % 1009 == 0;
>   }
> }
> {code}
> Although not yet implemented, the divisor in this RowSample could be configurable. RFiles
with sample data would store the fact that a RowSample with a divisor of 1009 was used to
generate sample data.



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