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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-3646) Duplicate entries when iterator emits entries past seek() range
Date Mon, 27 Apr 2015 15:12:39 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-3646?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14514261#comment-14514261
] 

ASF GitHub Bot commented on ACCUMULO-3646:
------------------------------------------

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

    https://github.com/apache/accumulo/pull/33#discussion_r29155217
  
    --- Diff: docs/src/main/asciidoc/chapters/iterator_design.txt ---
    @@ -145,8 +146,16 @@ alter the internal state of the Iterator.
     
     These methods simply return the current Key-Value pair for this iterator. If `hasTop`
returns true,
     both of these methods should return non-null objects. If `hasTop` returns false, it is
undefined
    -what these methods should return. Multiple calls to these methods should not alter the
state
    -of the Iterator like `hasTop`.
    +what these methods should return. Like `hasTop`, multiple calls to these methods should
not alter 
    +the state of the Iterator.
    +
    +When saving a Key or Value from a source iterator's `getTopKey` or `getTopValue` methods
    +for use after calling `next` on the source iterator (e.g., when cacheing keys or values
    +from the source iterator), it is important to copy the Key or Value into a new object

    +because the source iterator may reuse the Key or Value objects for performance reasons.
    --- End diff --
    
    I'm a little concerned about recommending to always copy the Key or Value is that returned
as it will drastically increase the number of created objects in the tserver and probably
tank performance. At the same time, I don't think I've ever done this myself (copy the Key/Value
in an iterator), but I haven't run into any issues that you're warning against (maybe it only
happens farther "down" the stack at the iterators reading off of disk?). How have you run
into this issue? Can we try to make this more specific?


> Duplicate entries when iterator emits entries past seek() range
> ---------------------------------------------------------------
>
>                 Key: ACCUMULO-3646
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-3646
>             Project: Accumulo
>          Issue Type: Bug
>          Components: client, mini, tserver
>    Affects Versions: 1.6.1
>         Environment: Ubuntu 14.04, Accumulo 1.6.1, Hadoop 2.6.0, Zookeeper 3.4.6
>            Reporter: Dylan Hutchison
>            Assignee: Dylan Hutchison
>            Priority: Minor
>             Fix For: 1.7.0
>
>
> The SortedKeyValueIterator's seek() method documents that an iterator may return keys
past the range passed to seek().  However, an iterator set at scan-time that returns values
past the range passed to seek() will return those keys multiple times if the client uses a
BatchScanner.  This does not occur when the client uses a Scanner. This has nothing to do
with the VersioningIterator. This has nothing to do with the entries actually in the table.
Also affects MiniAccumulo.
> If this is intended, we should update the SortedKeyValueIterator seek() documentation
with a warning that returning keys past the seek() range may result in a client seeing duplicate
keys. If this is not intended, then it is a bug.
> Test code: See [InjectTest|https://github.com/Accla/d4m_api_java/blob/master/src/test/java/edu/mit/ll/graphulo/InjectTest.java]
> * method {{testInjectOnScan_Empty}} fails because it uses a BatchScanner
> * method {{testInjectOnScan_Empty_Reg}} passes because it uses a Scanner
> In these methods, the [InjectIterator|https://github.com/Accla/d4m_api_java/blob/master/src/main/java/edu/mit/ll/graphulo/InjectIterator.java]
emits entries that go beyond the seek() range.  We confirm what is going on by placing a [DebugIterator|https://accumulo.apache.org/1.6/apidocs/org/apache/accumulo/core/iterators/DebugIterator.html]
right after.
> Logs when using the BatchScanner:
> notice that the "m1" row is returned twice:
> {noformat}
> 015-03-05 06:05:34,768 [graphulo.BranchIterator] INFO : class edu.mit.ll.graphulo.InjectIterator:
init on scope scan
> 2015-03-05 06:05:34,768 [graphulo.BranchIterator] INFO : class edu.mit.ll.graphulo.InjectIterator:
init on scope scan
> 2015-03-05 06:05:34,770 [iterators.DebugIterator] DEBUG: init(edu.mit.ll.graphulo.InjectIterator@e9fe846,
{}, org.apache.accumulo.tserver.TabletIteratorEnvironment@b99fd03)
> 2015-03-05 06:05:34,771 [iterators.DebugIterator] DEBUG: 0x516E9F1F seek((-inf,f%00;
: [] 9223372036854775807 false), [], false)
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> true
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopKey() -->
a1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> true
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopKey() -->
a1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopValue() -->
1
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F next()
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> true
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopKey() -->
c1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> true
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopKey() -->
c1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> true
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopKey() -->
c1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopValue() -->
1
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F next()
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> true
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopKey() -->
m1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> true
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopKey() -->
m1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> true
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopKey() -->
m1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F getTopValue() -->
1
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F next()
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> false
> 2015-03-05 06:05:34,772 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> false
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x516E9F1F hasTop() --> false
> 2015-03-05 06:05:34,770 [iterators.DebugIterator] DEBUG: init(edu.mit.ll.graphulo.InjectIterator@2528a1f1,
{}, org.apache.accumulo.tserver.TabletIteratorEnvironment@244a532a)
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA seek([f%00; : []
9223372036854775807 false,+inf), [], false)
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA hasTop() --> true
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA getTopKey() -->
m1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA hasTop() --> true
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA getTopKey() -->
m1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA hasTop() --> true
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA getTopKey() -->
m1 colF3:colQ3 [] 1425553534769 false
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA getTopValue() -->
1
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA next()
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA hasTop() --> false
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA hasTop() --> false
> 2015-03-05 06:05:34,773 [iterators.DebugIterator] DEBUG: 0x5DBB88BA hasTop() --> false
> {noformat}



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