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From joshelser <...@git.apache.org>
Subject [GitHub] accumulo pull request: ACCUMULO-3646 Update iterator doc on entrie...
Date Mon, 27 Apr 2015 15:12:09 GMT
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?


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