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https://issues.apache.org/jira/browse/ACCUMULO-3959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14709855#comment-14709855
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ASF GitHub Bot commented on ACCUMULO-3959:
------------------------------------------
Github user keith-turner commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/45#discussion_r37789259
--- Diff:
core/src/main/java/org/apache/accumulo/core/client/BatchScanner.java ---
@@ -16,19 +16,20 @@
*/
package org.apache.accumulo.core.client;
+import org.apache.accumulo.core.data.Range;
+
import java.util.Collection;
import java.util.concurrent.TimeUnit;
-import org.apache.accumulo.core.data.Range;
-
/**
* 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: https://issues.apache.org/jira/browse/ACCUMULO-3959
> 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|https://accumulo.apache.org/1.7/apidocs/org/apache/accumulo/core/client/BatchScanner.html]
> 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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