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From denine99 <...@git.apache.org>
Subject [GitHub] accumulo pull request: ACCUMULO-3646 Update iterator doc on entrie...
Date Mon, 27 Apr 2015 15:46:10 GMT
Github user denine99 commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/33#discussion_r29158839
  
    --- 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 --
    
    Hi Josh, 
      Take a look at the [Accumulo mail list posting here](https://mail-archives.apache.org/mod_mbox/accumulo-user/201504.mbox/%3C552E8941.8080908%40gmail.com%3E).
 This outlines my experience with aliasing from a Value in an RFile.  The consensus is that
aliasing is a good thing by default for performance reasons (less copying than if the base
iterator allocated new memory every read).
    
    Collapsing a bunch of columns into a single K/V is safe if the intermediary K/Vs are copied
each time.


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