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From "ASF GitHub Bot (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3959) Confusing wording on BatchScanner javadoc
Date Mon, 24 Aug 2015 18:55:47 GMT


ASF GitHub Bot commented on ACCUMULO-3959:

Github user keith-turner commented on a diff in the pull request:
    --- Diff: core/src/main/java/org/apache/accumulo/core/client/ ---
    @@ -16,19 +16,20 @@
     package org.apache.accumulo.core.client;
     import java.util.Collection;
     import java.util.concurrent.TimeUnit;
      * Implementations of BatchScanner support efficient lookups of many ranges in accumulo.
    + * BatchScanners are also appropriate for large, single ranges,
    + * as a BatchScanner will break those ranges up into separate RPCs
    + * provided the range spans more than one tablet
    + * and there are sufficiently many scan threads available.
    --- End diff --
    Maybe instead of suggesting how to use the batch scanner, we could focus more on describing
possible behavior?
      * May parallelize reading of data.  Multiple input ranges may be read in parallel or
sub ranges of individual input ranges may be read in parallel.
      * May return data in unsorted order.
      * May batch multiple ranges into a single RPC to a tserver.   
    Could still mention possible use cases like :
      * Looking up lots of small ranges
      * Parallelizing (spell check in web browser does not like that word) a computation over
an entire table using a large range w/ iterators.   This case may not return lots of data,
although lots of data may be read by the iterators.

> Confusing wording on BatchScanner javadoc
> -----------------------------------------
>                 Key: ACCUMULO-3959
>                 URL:
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: docs
>    Affects Versions: 1.6.3, 1.7.0
>            Reporter: Dylan Hutchison
>            Assignee: Dylan Hutchison
>            Priority: Minor
>              Labels: docuentation
>             Fix For: 1.6.4, 1.7.1
> The following sentence in the [BatchScanner Javadoc|]
has confused my colleagues into using Scanners and wondering why performance doesn't scale.
> bq. If you want to lookup a few ranges and expect those ranges to contain a lot of data,
then use the Scanner instead.
> Also regarding this next sentence, from what I see of the BatchScanner it will break
up "large Range objects" that span multiple extents (tablets) into multiple ranges, possibly
one for each tablet.
> bq. Use this when looking up lots of ranges and you expect each range to contain a small
amount of data.
> If the client is okay with unsorted order and it is okay with using multiple threads,
then isn't it always a better decision to use a BatchScanner than regular Scanner?  In the
worst case, one Range over a single row, the BatchScanner will perform the same as a regular
Scanner, ya?

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